Tag Archives: fungus

C-Rated, Fungi, Plant Pathogens

Septocyta ruborum (Lib.) Petrak. 1967

California Pest Rating for

Septocyta ruborum (Lib.) Petrak. 1967
(syn. Rhabdospora ramealis (Roberge ex Desm.) Sacc.)

Pest Rating: C
download pest rating
Responsible Party:

Heather J. Scheck, CDFA Primary Plant Pathologist/Nematologist. 204 West Oak Ave, Lompoc, CA
93463. 805-736-8050. plant.health[@]cdfa.ca.gov.

*NOTE:

You must be registered and logged in to post a comment. If you have registered and have not received the registration confirmation, please contact us at plant.health[@]cdfa.ca.gov.

Posted by ls

Fungi, Plant Pathogens

Marasmiellus Palmivorus

California Pest Rating for
Marasmiellus palmivorus (Sharples) Desjardin comb. prov.
Pest Rating: C

PEST RATING PROFILE

Initiating Event:   

None.  The risk of infestation of M. palmivorus in California evaluated and a permanent rating is herein proposed.

History & Status:

Background:   Marasmiellus palmivorus is a Basidiomycete fungus in the order Agaricales.  The species was described by Sharples in 1936, but, in the 1920s, was reported to have caused significant losses to oil palm and coconut in Malaysia 1920 (Pong et al., 2012).  In 1980, specimens of the fungus from coconut and oil palm were initially identified as Marasmiellus semiustus, a species that is generally regarded synonymous with M. palmivorus (CABI, 2018).  There has been confusion over the taxonomy of M. palmivorus and the species was previously attributed to the genus Marasmius (palmivorus).  However, Hemmes and Desjardin (2002) and Wilson and Desjardin (2005), in their taxonomic revision of the genus, regarded the genus Marasmius as a synonym of Marasmiellus until further DNA phylogenetic analysis is done to support its accurate identification (Pong et al., 2012).

Marasmiellus palmivorus can be saprophytic on a range of dead and dying plant material, or parasitic on tropical plants.  The species is reported to cause bunch rot disease on oil palm fruit, seeds, and seedlings in Malaysia (Almaliky et al., 2012; Pong et al., 2012), and is associated with leaf infection and bud rot of coconut, also causing embryo and shoot rot in germinating nuts and post-emergence damping off disease in Malaysia (Amaliky et al., 2013; CABI, 2018).  Synonymous species of M. palmivorus have also been recorded on pineapple causing trunk and root rot, and root rot of maize and sugarcane (CABI, 2018). In Hawaii, M. palmivorus was listed as a wood-rotting basidiomycete fungus of native and exotic plant species (Gilbertson et al., 2002).

In California, during March 2017, Marasmiellus palmivorus was detected on ginger flower stems from a shipment of ginger cut flowers that originated in Hawaii and was intercepted in Humboldt County by Humboldt County Agricultural officials. The pathogen was identified at the CDFA Plant Pathology Lab and was given a Q rating, which resulted in the destruction of the shipment.  The pathogen is not known to be established in California.

Disease Development: The fungus is normally saprophytic on decaying and dead materials.  It spreads to a new food source by growth of its hyphal strands or rhizomorphs and requires plenty of moisture for growth and development.  Not much is known of the biology of the fungus.  It is presumed that the fungus becomes parasitic once it has attained a certain inoculum level as infection by a small amount of spores or mycelium is unlikely (Turner, 1981 in CABI, 2018).

Dispersal and spread: Infected plants including flowers, fruits, leaves, roots, stems, true seeds, wood, contaminated coconut seed-nuts, plant decaying and dead materials, windblown rain, water-splash, air-currents (CABI, 2018).

Hosts: Ananas comosus (pineapple), Alpini purpurata (red ginger), Cocos nucifera (coconut), Elaeis guineensis (African oil palm), Etlingera elatior (torch ginger), Hevea brasiliensis (rubber), Musa x paradisiaca (plantain), Zingiber officinale (ginger) (Almaliky et al., 2012, 2013; CABI, 2017; Farr & Rossman, 2017; Gilbertson et al., 2002).

Symptoms:  Marasmiellus palmivorus causes bunch rot disease of oil palm in Malaysia.  In pathogenicity tests conducted by Almaliky et al. (2012), symptoms in fruit included a wet, discolored soft rot that extended upward to the tip of the fruit; infected seeds showed pre-emergence damping off consisting of seed decay, reddish-brown discoloration of shoots and radicles, failure to germinate, and post-emergence damping off; infected seedling initially showed chlorosis that turn brown to black rot lesions on the base of lower leaves, and roots were usually soft, rotten, water-soaked and dark brown or black in color with white mycelia covering the roots and crowns partially. Seedlings reared in a greenhouse developed root and crown rot and leaf blight.  Initial necrosis at the bases of leaves subsequently caused extensive discoloration, softening, rapid drying and wilting of leaves.  Rotting of seedlings initiated near the soil line and moved downwards and upwards resulting in parts of stems and base of leaves turning brown to black in color.  .  Dense white mycelia were formed on the lower stem of base of seedlings.  Basidiocarps (mushroom-like fruiting bodies) were formed at the base of seedlings near the crown.  The fungus also caused post-emergence damping off on coconut seedlings in Malaysia (Almaliky et al., 2013).  The researchers also showed that isolates from coconut were pathogenic to oil palm.

Damage Potential: In California, certain hosts, such as, ginger and plantain that are grown as ornamental plants by nurseries, small businesses, hobbyists, and private residents may be affected by the fungus if it were able to establish within high moisture environments.    

Worldwide Distribution:  Africa: Congo Democratic Republic, Nigeria; Asia: Brunei Darussalam, India (Andaman and Nicobar Islands), Indonesia, Malaysia; Central America and Caribbean: Trinidad and Tobago, North America: USA (Hawaii), South America: Colombia; Oceania: Fiji, Papua New Guinea (CABI, 2017; Farr & Rossman, 2017; Gilbertson et al., 2002).

Official Control: Marasmiellus palmivorus is on the ‘Harmful Organism’ lists for Guatemala, Nicaragua, and Peru (USDA-PCIT, 2017).

California Distribution: Marasmiellus palmivorus has not been reported from California.

California Interceptions: To date, Marasmiellus palmivorus has been detected once in a single shipment of ginger cuttings that were shipped from Hawaii and intercepted in Humboldt County.

The risk Marasmiellus palmivorus would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Marasmiellus palmivorus requires high amounts of moisture to grow and develop. It may be able to establish only in very limited areas of the State, if at all.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 1

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: The host range is limited to some tropical plants that include, pineapple, African oil palm, coconut, plantain, rubber, and ginger.  It is also a saprophytic and feeds on dead and decaying material.  Presently, its pathogenicity has only been reported on coconut and Oil palm.

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Infected plants including flowers, fruits, leaves, roots, stems, true seeds, wood, contaminated coconut seed-nuts, plant decaying and dead materials, windblown rain, water-splash, air-currents.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Potential losses to oil palm in Malaysia have only been reported.  Economic impact due to the fungus are largely not known.  Most hosts of the fungus are not commercially grown in California. Other hosts, such as, ginger and plantain that are grown as ornamental plants by nurseries may be affected by the fungus if it were able to establish within high moisture environments.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: B

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 1

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact:  Under high moisture environments, Marasmiellus palmivorus may impact ornamental plantings of host plants in home/urban gardens.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Marasmiellus palmivorus: Low (8)

Add up the total score and include it here.

–Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is ‘Not established’ in California.

Score: (0)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Marasmiellus palmivorus is C.

References:

Almaliky, B. S. A., M. A. Zainal Abidin, J. Kadir, and M. Y. Wong.  2012.  Pathogenicity of Marasmiellus palmivorus (Sharples) Desjardin comb. prov. on oil palm Elaeis guineensis.  Wulfenia 19: 1-17.

Almaliky, B. S. A., J. Kadir, M. Y. Wong, and M. A. Zainal Abidin.  2013.  First report of Marasmiellus palmivorus causing post-emergence damping off on coconut seedlings in Malaysia. Plant Disease 97: 143.

CABI, 2017.    Marasmius palmivorus (oil palm bunch rot) full datasheet.  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/34926

Farr, D. F., and A. Y. Rossman.  2017.  Fungal Databases, U. S. National Fungus Collections, ARS, USDA. Retrieved April 27, 2017, from http://nt.ars-grin.gov/fungaldatabases/

Gilbertson, R. L., D. M. Bigelow, D. E. Hemmes, and D. E. Desjardin.  2002.  Annotated check list of wood-rotting Basidiomycetes of Hawai’i.  Mycotaxon 82: 215-239

Pong, V. M., M. A. Zainal Abidin, B. S. A. Almaliky, J. Kadir, and M. Y. Wong.  2012.  Isolation, fruiting and pathogenicity of Marasmiellus palmivorus (Sharples) Desjardin (comb.prov.) in oil palm plantations in West Malaysia.  Pertanika Tropical Agricultural Science 35 (S): 38-48.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System. April 26, 2017, 5:04:18 pm CDT.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

*NOTE:

You must be registered and logged in to post a comment.  If you have registered and have not received the registration confirmation, please contact us at plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

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♦  Comments may be edited prior to posting to ensure they are entirely germane.

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Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Diaporthe pseudophoenicicola R. R. Gomes, C. Glienke & Crous 2013

California Pest Rating for
Diaporthe pseudophoenicicola R. R. Gomes, C. Glienke & Crous 2013
Pest Rating: C

PEST RATING PROFILE
Initiating Event:

On June 15, 2017, a shipment of an unknown plant, exhibiting symptoms of leaf spotting and destined to a commercial florist in Los Angeles County, was intercepted by the CDFA Dog Team in Los Angeles County.  The shipment had originated in Kilgore, Texas.  A sample of symptomatic leaves was submitted to the CDFA Plant Pathology Lab for disease diagnosis.  On July 7, 2017, Suzanne Latham, CDFA plant pathologist, detected the fungal pathogen, Diaporthe pseudophoenicicola, in culture and confirmed its identity by PCR testing, as the cause for the disease.  Later, on July 19, 2017, the same pathogen was detected in a date palm (Phoenix dactylifera) sample exhibiting decline and canker symptoms and collected from a tree located off Interstate 5 (I-5), in Orange County.  The sample was collected by Orange County Agricultural officials and sent to the CDFA Plant Pathology Lab for diagnosis.  Suzanne Latham detected D. pseudophoenicicola in culture and confirmed its identity by multi-locus sequencing.  Later, the identity of the pathogen was also confirmed by the USDA APHIS Mycology and Nematology Genetic Diversity and Biology Laboratory at Beltsville, Maryland (Kennedy, 2017).   The current status and rating of D. pseudophoenicicola in California is assessed here and a permanent rating is proposed.

History & Status:

Background:  Diaporthe pseudophoenicicola is a fungal plant pathogen belonging to the order Diaporthales.  The species was named after its morphological similarity to Diaporthe phoenicicola, which was originally isolated from dead leaves of Mangifera indica in Pakistan, however, later reported to differ morphologically from D. phoenicicola (Gomes et al., 2013).  Diaporthe pseudophoenicicola is the sexual state of the pathogen, whereas, the asexual state belongs to the genus Phomopsis.  Presently, D. pseudophoenicicola has only been reported from China, Iraq, and Spain (Farr & Rossman, 2017; Gomes, et al., 2013).

The asexual state of the fungal pathogen has been detected in California prior to the 2017 detection.  In 2007, during a CDFA survey for palm wilt in Southern California, 16 detections were made of unidentified Phomopsis sp. on Phoenix canariensis, P. dactylifera, and P. reclinata in 10 counties.   Only recently, was the Phomopsis species that was detected on P. dactylifera in Riverside County, identified through DNA sequencing as P. pseudophoenicicola (syn. Diaporthe pseudophoenicicola), thereby, indicating that this pathogen has already been established in California for at least 10 years.  Complete identification of the remaining Phomopsis sp. is pending (personal communication: Suzanne Latham, CDFA).

Disease Development:  While specific information is lacking, it is likely that plant infection and disease development caused by Diaporthe pseudophoenicicola are similar to those caused by other species of Diaporthe occurring as plant pathogens, endophytes or saprobes.  The fungus produces ascospores (sexual spores) in perithecia (sexual fruiting bodies) and conidia (asexual spores) in pycnidia on dead twigs and leaves.  Conidia are the main inoculum causing primary and secondary infections and are spread to host plants by splashing rains.  Ascospores may be involved in long distance dispersal of the pathogen.  The fungus is likely to overwinter as mycelium and/or as conidia within pycnidia (Agrios, 2005).

Dispersal and spread: Windblown/splashing rain and irrigation water, pruning tools, possibly insects, and animals can spread fungal spores to non-infected plants.

Hosts: Mangifera indica (mango), Phoenix dactylifera (date palm), P. canariensis (Canary Island palm) (Farr & Rossman, 2017; Gao et al., 2017; Gomes et al., 2013).

Symptoms:  Diaporthe pseudophoenicicola causes symptoms of dieback and canker in infected mango and date palm.  Dead tops of green leaves have been reported for date palms (Farr & Rossman, 2017; Gomes et al., 2013).

Damage Potential: Quantitative losses caused by Diaporthe pseudophoenicicola have not been reported. The pathogen causes dieback and cankers in mango and date palm.  Therefore, if left uncontrolled, infections may result in reduced fruit and plant production and marketability.  In California, nurseries and other growers of mango and date palms plants may be at risk of damage caused by this pathogen.

Worldwide Distribution: Asia: China, Iraq; Europe: Spain (Farr & Rossman, 2017; Gomes et al., 2013); North America: USA (California) (see: “Initiating Event”).

Official Control: No official control is reported for Diaporthe pseudophoenicicola or Diaporthe spp., however, Phomopsis spp. is presently on the ‘Harmful Organism List’ for French Polynesia (USDA PCIT, 2017).  Currently, D. pseudophoenicicola has a temporary Q rating in California.

California Distribution:  Los Angeles, Orange, and Riverside Counties.

California Interceptions: There has been only one interception.  On July 7, 2017, Diaporthe pseudophoenicicola was detected in a shipment of an unknown plant that originated in Texas (see: ‘Initiating Event’).

The risk Diaporthe pseudophoenicicola would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Mango and palm are the only known hosts and are grown in California.  Diaporthe pseudophoenicicola may be able to infect its hosts under wet conditions and is therefore, only likely to establish in very limited regions of the State where mango and palm are grown mainly Southern California.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 1

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: The host range of the pathogen is presently limited to Mangifera indica and Phoenix dactylifera.

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Diaporthe pseudophoenicicola has high reproductive potential with an abundant production of spores, however, the spores are dependent on splashing water for dispersal.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 2

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Quantitative losses caused by Diaporthe pseudophoenicicola have not been reported. Under favorable wet conditions for spread and disease development the pathogen may cause dieback and cankers in mango and palm.  Therefore, if left uncontrolled, infections may result in reduced fruit and plant production and marketability.  In California, nurseries and other growers of mango and date palms plants may be at risk of damage caused by this pathogen.,

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact:  The pathogen may impact palms used as ornamental plantings in commercial and private environments.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Diaporthe pseudophoenicicola: Medium (9)

Add up the total score and include it here.

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is Low.  The pathogen is already established in at least three counties in Southern California.

Score: (-1)

-Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8

Uncertainty:  

Identification of Phomopsis sp. (asexual state of Diaporthe) detected during the 2007 CDFA survey, is pending.  Positive identification may provide new information on the distribution and hosts of D. pseudophoenicicola in California, while further stabilizing its currently proposed rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Diaporthe pseudophoenicicola is C.

References:

Agrios, G. N.  2005.  Plant Pathology Fifth Edition.  Elsevier Academic Press.  922 p.

Farr, D. F., and A. Y. Rossman.  2017.  Fungal Databases, U. S. National Fungus Collections, ARS, USDA. Retrieved September 20, 2017, from http://nt.ars-grin.gov/fungaldatabases/

Gao, Y., F. Liu, W. J. Duan, P. W. Crous, and L. Cai.  2017.  Diaporthe is paraphyletic. IMA Fungus 8(1): 153-187.

Gomes, R.R., C. Glienke, S. I. R. Videira, L. Lombard, J. Z. Groenewald, and P. W. Crous.  2013.  Diaporthe: a genus of endophytic, saprobic and plant pathogenic fungi. Persoonia 31: 1-41.

Kennedy, A. H.  2017.  Email from A. H. Kennedy, Molecular Biologist, USDA APHIS Mycology and Nematology Genetic Diversity and Biology Laboratory, Beltsville, Maryland, to Suzanne Latham, Plant Pathologist, CDFA Plant Pest Diagnostics Branch, dated September 01, 2017, 5:14 am.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System. Sept. 20, 2017, 2:11:43 pm CDT.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

*NOTE:

You must be registered and logged in to post a comment.  If you have registered and have not received the registration confirmation, please contact us at plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Colletotrichum cliviae Y.L. Yang, Zuo Y. Liu, K.D. Hyde & L. Cai, 2009

California Pest Rating for
Colletotrichum cliviae Y.L. Yang, Zuo Y. Liu, K.D. Hyde & L. Cai, 2009
PEST RATING: B
PEST RATING PROFILE
Initiating Event:

On October 17, 2017, diseased leaves of variegated croton plants (Codiaeum variegata) exhibiting leaf spotting symptoms, were collected from a nursery in San Diego, by San Diego County officials and sent to the CDFA Plant Pathology Laboratory for diagnoses.  The shipment of croton plants had originated from Florida.  On November 20, 2017, Suzanne Latham, CDFA plant pathologist, identified the pathogen, Collectotrichum cliviae, as the cause for the disease. Furthermore, during 2015-2016, CDFA detections of anthracnose disease of Cymbidium sp., Aglaonema sp., and Dieffenbachia sp. plants in nurseries in San Diego County in California, were attributed to Colletotrichum cf. cliviae (‘cf’ in biological terminology means ‘a significant resemblance to’).  Those detections initiated, and were included in, a pest rating assessment for the closely similar species, C. cliviae, which was eventually given a permanent B-rating. However, those detections were recently shown to be, instead, C. aracearum (Kennedy, 2017; Latham, 2017).  The recent detection of C. cliviae in San Diego marked the first record of this pathogen in California. Consequently, the infected plants were treated by the nursery and are to be periodically re-inspected (Walber, 2017).  The risk of the introduction and establishment of C. cliviae, and its current rating in California are re-evaluated here.

History & Status:

Background:  Colletotrichum cliviae causes anthracnose and leaf blight disease in its host plants.  The fungal pathogen was originally reported from Clivia miniata (clivia/flame/bush/kaffir lily) leaves growing in Yunnan Province, China and reported as not being host-specific (Yang et al., 2009). Since then, C. cliviae has been found on few tropical and subtropical hosts from China, India, Brazil, and recently, from the USA (California).

Hosts: Arundina graminifolia (Bamboo orchid), Camellia sinensis (tea plant), Clivia miniata (Kaffir lily), Capsicum annuum (pepper), Capsicum sp., Cymbidium hookerianum (orchid), C. pendulum, Glycine max (soybean), Mangifera indica (mango) Phaseolus sp. (bean), Ricinus communis (castor), Saccharum sp., Zamioculcas zamiifolia (Barbieri et al., 2017; Chowpadda et al., 2014; Diao et al., 2017; Farr & Rossman, 2016; Lui et al., 2015; Saini et al., 2017; Sharma et al., 2014; Vieira et al., 2014; Yang et al., 2009; Zhang & Li, 2017).  The recent host, Codiaeum variegata (variegated croton) is added to this list (see ‘Initiating Event’).

Symptoms:  Generally, Colletotrichum-infected host plants exhibit symptoms of anthracnose which include dark brown leaf, stem and fruit spots, fruit rot, and wilting of leaves which often result in dieback and reduction in plant quality. Colletotrichum cliviae produce dark brown to black, ellipsoid lesions in orchid leaves of Cymbidium hookerianum and Arundina graminifolia.  The lesions contain pale yellow conidial (spore) masses (Yang et al., 2011).

Damage Potential:  Anthracnose disease caused by Colletotrichum cliviae can result in reduced plant quality and growth, fruit production and marketability.   Estimates of yield/crop loss due to this pathogen have not been reported. However, in California, nursery and greenhouse production of orchids, croton, and other host plants would be particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species.  In California’s cultivated fields, disease development may be sporadic as it is affected by levels of pathogen inoculum and environmental conditions.

Disease Cycle:  It is likely that Colletotrichum cliviae has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on plant residue in soil, on infected plants, and on seeds.  During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers.   Conidia are transmitted to host plants.  Humid, wet, rainy weather is necessary for infection to occur.  These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem under controlled environments of greenhouses.  Conidia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue.

Transmission:  Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution: Asia: China, India; South America: Brazil (Farr & Rossman, 2016; Liu et al., 2015; Vieira et al., 2014; Yang et al., 2011).

Official Control:  Colletotrichum cliviae is reportable to the USDA.

California Distribution: Colletotrichum cliviae is not established in California.

California Interceptions:  Only one interception from Florida is recorded (see ‘Initiating Event).

The risk Colletotrichum cliviae would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Similar to other species of Colletotrichum, C. cliviae requires humid, wet, rainy weather for conidia to infect host plants. This environmental requirement may limit the ability of the pathogen to fully establish and spread under dry field conditions in California.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Presently, the host range of Colletotrichum cliviae is limited to few plant species in eight different families – mainly economically important orchid, mango, and nursery ornamentals.

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: The pathogen has high reproductive potential and conidia are produced successively.  They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Under suitable, wet climates, the pathogen could lower plant growth, fruit production and value and trigger the loss of markets. Nursery orchids and ornamentals, and mango production could be negatively affected.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: The pathogen could significantly impact cultural practices or home garden plantings.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E 

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Colletotrichum cliviae: Medium (11)

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Colletotrichum cliviae to California = (11).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Not established in California (-1).

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11.

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose pathogen, Colletotrichum cliviae is B.

References:

Diao, Y.-Z., C. Zhang, F. Liu, W. –Z, Wang, L. Liu, L. Cai,, and X. –L. Liu.  2017.  Colletotrichum species causing anthracnose disease of chili in China. Persoonia 38: 20-37.

Barbieri, M. C., G., M. Ciampi-Guillardi, S. R. G. Moraes, S. M. Bonaldo, F. Rogerio, R. R. Linhares, and N. S. Massola Jr.  2017.  First report of Colletotrichum cliviae causing anthracnose on soybean in Brazil. Plant Disease 101: 1677.

Chowpadda, P., C. S. Chethana, R. P. Pant, and P. D. Bridge.  2014.  Multilocus gene phylogeny reveals occurrence of Colletotrichum cymbidiicola and C. cliviae on orchids in north east India.  Journal of Plant Pathology 96: 327-334.

Farr, D. F., & A. Y. Rossman.  2016.  Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Retrieved April 3, 2016, from

http://nt.ars-grin.gov/fungaldatabases/

Kennedy, A.  2017.  Email from A. H. Kennedy, Molecular Biologist, National Identification Services, USDA APHIS PPQ PM to John Chitambar, CDFA, sent: August 29, 2017, 12:54 pm.

Latham, S.  2017.  Email from A. H. Kennedy, Molecular Biologist, National Identification Services, USDA APHIS PPQ PM to Suzanne Latham, CDFA, sent: August 18, 2017, 12:11 pm.

Liu, F., B. S. Weir, U. Damm, P. W. Crous, Y. Wang, B. Liu, M. Wang, M. Zhang, and L. Cai. 2015. Unravelling Colletotrichum species associated with Camellia: employing ApMat and GS loci to resolve species in the C. gloeosporioides complex. Persoonia 35: 63-86.  http://dx.doi.org/10.3767/003158515X687597.

Saini, T. J., S. G. Gupta, and R. Anandalakshmi.  2017.  Detection of chili anthracnose caused by Colletotrichum cliviae in India. Australasian Plant Disease Notes 12: 33.

Sharma G., A. K. Pinnaka, and B. D. Shenoy.  2013. ITS-based diversity of Colletotrichum from India. Current Research in Environmental & Applied Mycology 3: 194–220.

Vieira, W.A.S., S. J. Michereff, M. A. de Morais, Jr., K. D. Hyde, and M. P. S. Camara. 2014.  Endophytic species of Colletotrichum associated with mango in northeastern Brazil. Fungal Diversity 67: 181-202.

Walber, T.   2017.  Email from G. Hernandez, San Diego County Department of Agriculture/Weights & Measures to T. Walber, CDFA Interior Pest Exclusion.  Dated: December 01, 2017, 11:28:29 am.

Weir, B. S., P. R. Johnston, and U. Damm.  2012.  The Colletotrichum gloeosporioides species complex.  Studies in Mycology, 73:115-180. DOI:10.3114/sim0011.

Yang, Y., L. Cai, Z. Yu, Z. Liu, and K. D. Hyde.  2011.  Colletotrichum species on Orchidaceae in southwest China.  Cryptogamie, Mycologie, 2011, 32 (3): 229-253.

Yang, Y.L., Z. Y. Liu, L. Cai, K. D. Hyde, Z. N. Yu, and E. H. C. McKenzie. 2009. Colletotrichum anthracnose of Amaryllidaceae. Fungal Diversity 39: 123-146.

Zhou, Z., and Y. L. Li.  2017.  First report of Colletotrichum cliviae causing anthracnose on Zamioculcas zamiifolia in Henan Province, China. Plant Disease 101(5): 838.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

*NOTE:

You must be registered and logged in to post a comment.  If you have registered and have not received the registration confirmation, please contact us at plant.health[@]cdfa.ca.gov.

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Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

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♦  Comments may not be posted if they:

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PEST RATING: B

Posted by ls

Fungi, Plant Pathogens

Ustilago esculenta

1 Comment
California Pest Rating for
Ustilago esculenta Henn. 1895
PEST RATING: A

PEST RISK PROFILE

Initiating Event:   

On October 19 and 20, 2017, Manchurian wild rice plants with slightly swollen lower stems, were collected by Riverside County Agricultural officials, from a private company, in Riverside County and sent to the CDFA’s Plant Pathology Lab for possible detection of the smut fungus, Ustilago esculenta.  On November 20, 2017, Cheryl Blomquist, CDFA plant pathologist, detected U. esculenta, by PCR and sequencing, from the swollen, white interior plant tissue.   The current status and risk of U. esculenta to California is assessed here and a permanent rating is proposed.

History & Status:

Background:  Ustilago esculenta is a biotrophic (i.e., it has a long-term, non-lethal feeding relationship with an infected plant) smut fungus that incites formation of swollen culms or smut galls in the apical internodal (stem) region of perennial Manchurian wild rice, Zizania latifolia.  These swollen culms or smut galls are edible and have unique flavor and delicacy.  The swollen culms are consumed as a vegetable in India (Manipur), China, Japan, and Taiwan (Chung & Tzeng, 2004; Jose et al., 2016; Terrell & Batra, 1982).  In China and Japan, it is cultivated as a commercial food crop (Jose et al., 2016).  Furthermore, in Taiwan, and southern China, the production of galls occurs during the season of tropical storms and provides an alternate food source to consumers when cultivation of other vegetables is negatively affected.  Therefore, the fungus is considered highly beneficial and economically important (Chung & Tzeng, 2004).   Hennings (1895) originally discovered the pathogen, Ustilago esculenta in its infected host, Zizania latifolia, in China.

In the USA, Manchurian wild rice, Zizania latifolia, is prohibited entry into the country due to the smut fungus, Ustilago esculenta, that it carries (USDA, 2017).  Native species of wild rice may be at risk of infection and loss of production particularly since the fungus prevents development of inflorescences, thereby, affecting seed production (Terrell & Batra, 1982; Yamaguchi, 1990).

In 1991, an illegal 0.05-ha planting of Manchurian wild rice infected with Ustilago esculenta was discovered in a field near Modesto, California and marked the first report of the disease in a field situation in North America.  The plants had been brought into the USA in violation of federal quarantines and were eradicated (Watson et al., 1991).   In 1999, the host and pathogen were discovered in two small grower’s plots (approximately 2-ha total) in Baton Rouge, Louisiana.  The plants were eradicated in 2000 (NPAG, 2001).

Disease Development: Ustilago esculenta spends its entire life cycle in the host plant.  The fungus grows within and between plant cells in the stem tissues, particularly near the apical meristem.  However, the fungus is not systemically distributed throughout the entire plant and does not invade leaf and root tissue (Chen & Tzang, 1999, Jose et al., 2016).  Chen and Tzang (1999), using PCR technology, found the fungal DNA in the growth tip of Manchurian wild rice plants and not in leaves and healthy plant tissue.  They also detected the fungus in the sheath of infected plants even when there were no outward signs of its presence.  The fungus prevents production of inflorescence and galls develop at the internode region beneath the apical meristem.  Galls are formed within 10-15 days even though the plants may have been planted in the soil for over 8 months. Internally, gall formation involves hypertrophy (increase in cell size), hyperplasia (increase in cell numbers), and presence of mucilaginous cavities (Chan & Thrower, 1980).  At this developmental stage, the inner tissue of a gall appears white and filled with fungal hyphae which later develop to form dark teliospores (sexual spores) within the gall.  Teliospore formation is favored at temperatures greater than 28°C (Chung & Tzeng, 2004). In China, the edible galled plants are harvested for consumption prior to the production of teliospores.  With time, black longitudinal streaks appear, and eventually, the entire stem turns black and deteriorates.  Furthermore, a lack of nutrients in a plant or low water level in a field initiate earlier production of the reproductive stage of the fungus, thereby, reducing quality and yield of the plants (Yamaguchi, 1990).  The optimum temperature for fungal growth is 20-28°C and the optimum pH range is 4-7. The fungus may overwinter as mycelium and teliospores in the grass rhizomes and be transmitted into new shoots through asexual propagation of the plant.  Alternatively, teliospores from decomposed galls, may survive in soil (Chung & Tzeng, 2004).  Jose et al., (2016) detected spores and fragmented hyphae in the rhizomes throughout the year, including the month of January during which the above ground culms degenerated, thereby, suggesting that it may serve as inoculum for infection.

Dispersal and spread: Plant rhizomes, galled stems, and soil (Jose et al., 2016; Chung & Tzeng, 2004).

Hosts: Zizania spp. in the family Poaceae: Z. aquatica, Z. latifolia (syn. Z. caduciflora), and Zizania sp.

Symptoms: Ustilago esculenta stimulates the swelling of the culms of its host grass plants resulting in the formation of edible galls at the internodal region beneath the apical meristem (stem base).  The galls are about 3-4 cm in width and 15-20 cm in length (Chung & Tzeng, 2004).  Infected plants do not show any typical disease symptoms despite the internal presence of the fungus (Jose et al., 2016). Experimentally, plant infected with U. esculenta showed a decrease in height, but significant increase in above-ground biomass and higher chlorophyll content (Yan et al., 2013).

Damage Potential: Ustilago esculenta prevents the production of inflorescences in host plants thereby, significantly reducing seed production and resulting in great yield loss (Terrell & Batra, 1982; Chen & Tzeng, 1999).  Production of wild rice, including near relatives of Zizania latifolia, in California may be significantly reduced by the fungus.

Worldwide Distribution: Asia: Cambodia, China, Hong Kong, India, Japan, Laos, Malaysia, Myanmar, (east and south Asia), Taiwan, Thailand, (former) USSR, Vietnam; North America: USA (District of Columbia) (Farr & Rossman, 2017).

Official Control:  Ustilago esculenta, with its host plant, Zizania spp., are prohibited from being imported or offered for entry into the United States by the USDA, and are on the Prohibited Articles List under Federal Regulations 7CFR 319.37-2 (USDA, 2017).

California Distribution: Ustilago esculenta is not established in California.

California Interceptions:  In 1998, there was one interception of Manchurian wild rice infested with Ustilago esculenta destined to a private business in San Bernardino County.  The shipment was destroyed.

In 1991, a foreign-sourced, illegal planting of Manchurian wild rice infected with Ustilago esculenta was detected in a field near Modesto.  The plants were eradicated.

The risk Ustilago esculenta would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Ustilago esculenta is likely to establish wherever wild rice, Zizania, is cultivated in California.  California wild rice is grown under warm, dry, clear days, and a long growing season; mostly on fine-textured, poorly-drained soils (Farrar, 2000).   Since the fungus is limited to Zizania spp., and is likely to establish wherever native species of wild rice are grown in California, its potential distribution is considered widespread and a ‘High” rating is given to this category.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 3

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range:  The host range is limited to Zizania

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: The fungus is biotrophic and is dependent on the spread infested galled plants for long distance spread.  It is also transmitted in propagative rhizomes and soil.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Ustilago esculenta prevents the production of inflorescences in host plants thereby, drastically reducing seed production and resulting in great yield loss.  The fungus and its vectoring host, Zizania latifolia, are prohibited entry in the USA , and would be a threat to native species of wild rice that are grown in California

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C, D, E

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Ustilago esculenta, either through the establishment of infected Zizania latifolia or its direct impact on the stand and cultivation of California native wild rice species, can result in reducing native stands of wild rice by reducing seed production, thereby, disrupting aquatic plant and animal communities, critical habitats, and lowering biodiversity.  This could result in additional official treatment programs. A “High” rating is given to this category.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: A, C, D

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 3

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Ustilago esculenta: High (13)

Add up the total score and include it here.

-Low = 5-8 points

-Medium = 9-12 points

–High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is Low.  Ustilago esculenta is not established in California.

Score: 0

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 13

Uncertainty:   

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Ustilago esculenta is A.

References:

Chan, Y-S., and L. B. Thrower.  1980.  The host-parasite relationship between Zizania caduciflora Turcz. and Ustilago esculenta P. Henn. 1. Structure and development of the host and host-parasite combination.  New Phytopathology 85: 201-207.

Chen, R-S., and D. D-S. Tzeng.  1999.  PCR-mediated detection of Ustilago esculenta in water oat (Zizania latifolia) by ribosomal internal transcribed spacer sequences.  Plant Pathology Bulletin 8: 149-156.

Chung, K., and D. D. Tzeng.  2004.  Nutritional Requirements of the Edible Gall-producing Fungus Ustilago esculenta. Journal of Biological Sciences, 4(2), 246-252.

Farr, D. F., and A. Y. Rossman.  2017.  Ustilago esculenta.  Fungal databases, U.S. National Fungus Collections, ARS, USDA. Retrieved November 28, 2017, from https://nt.ars-grin.gov/fungaldatabases/

Farrar, K.  2000.  Crop profile for wild rice in California. California Pesticide Impact Assessment Program, University of California, Davis, CA. http://www.ipmcenters.org/CropProfiles/docs/cawildrice.pdf

French, A.M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento (Updated online version by T. Tidwell, May 2, 2017).

Jose, R. C., S. Goyari, B. Louis, S. D. Waikhom, P. J. Handique, and N. C. Talukdar.  2016.  Investigation on the biotrophic interaction of Ustilago esculenta on Zizania latifolia found in the Indo-Burma biodiversity hotspot.  Microbial Pathogenesis 98: 6-15.

NPAG.  2001.  NPAG report sent to Trillium.  20. Ustilago esculenta (Basidiomycota: Ustilaginomycetes: Ustilaginaceae) wild rice smut.  New Pest Advisory Group Plant Epidemiology and Risk Analysis Laboratory, Center for Plant Health Science & Technology.

Terrell, E. E., and L. R. Batra.  1982.  Zizania latifolia and Ustilago esculenta, a grass-fungus association. Economic Botany 36: 274-285.

USDA.  2017.  Plants for plant manual. United States Department of Agriculture.  First edition March 2017.

Watson, T., T. E. Tidwell, and D. G. Fogle.  1991.  Smut of Manchurian wild rice caused by Ustilago esculenta in California.  Plant Disease 95: 1075. DOI: 10.1094/PD-75-1075D.

Yamaguchi, M. (1990). Asian vegetables. In J. Janick & J. E. Simon (Eds.), Advances in new crops, 387-390. Timber Press, Portland, OR.

Yan, N., X-Q. Wang, X-F. Xu, D-P. Guo, Z-D. Wang, J-Z. Zhang, K. D. Hyde, and H-L. Liu.  2013.  Plant growth and photosynthetic performance of Zizania latifolia are altered by endophytic Ustilago esculenta infection. https://doi.org/10.1016/j.pmpp.2013.05.005

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

*NOTE:

You must be registered and logged in to post a comment.  If you have registered and have not received the registration confirmation, please contact us at plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

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PEST RATING: A

Posted by ls

Fungi, Plant Pathogens

Colletotrichum aracearum

California Pest Rating for
Colletotrichum aracearum L. W. Hou & L. Cai 2016
PEST RATING: B
PEST RATING PROFILE
Initiating Event:  

On July 28, 2017, diseased Cymbidium sp. plants exhibiting leaf spots, were detected by the CDFA Dog Team, in a shipment of plants that had originated in and was destined to a private resident in San Diego County.  Symptomatic leaves were sent to the CDFA Plant Pest Diagnostics Branch for diagnosis.  On August 21, 2017, Suzanne Latham, CDFA plant pathologist, detected the fungal pathogen, Colletotrichum aracearum, in culture from the leaf spots.  The identity of the pathogen was also confirmed by the USDA APHIS National Identification Services at Beltsville, Maryland (Kennedy, 2017).  Currently, C. aracearum has a temporary ‘Q’ rating.  The risk of introduction and establishment of C. aracearum in California is assessed and a permanent rating is proposed herein.

History & Status:

Background:  Colletotrichum aracearum causes anthracnose disease in its host plants. The recently described species (Hou et al., 2016) has only been reported from China, until its detection in California, USA.   In California, prior to the July 28, 2017 detection of Colletotrichum aracearum (see ‘Initiating Event’), there had been several detections of the pathogen which was then identified as Colletotrichum cf. cliviae (‘cf’ in biological terminology means ‘a significant resemblance to’).  However, those detections were recently shown to be C. aracearum (Kennedy, 2017; Latham, 2017).   The first detection of C. aracearum (then identified as Colletotrichum cf. cliviae) was made on April 28, 2015, from diseased Dieffenbachia sp. plants exhibiting leaf spots and detected in a nursery in San Diego County during regulatory nursery inspections by the San Diego County Agricultural officials. This marked a probable new U.S. record by the USDA National Identification Services at Beltsville, Maryland. Several detections followed from different nurseries within San Diego County.  On June 11, 2015 and August 19, 2015, the same pathogen was detected in Chinese evergreen (Aglaonema sp.) leaves from cuttings that were shipped from Guatemala and intercepted by San Diego County, and from diseased Aglaonema sp. plants detected during regulatory nursery inspections.  On December 3, 2015 and April 20, 2016, infected Aglaonema sp. were intercepted in plant shipments from Costa Rica, and on April 29, 2016, during  regulatory nursery inspections, the pathogen was detected in Cymbidium sp. orchid plants showing leaf spots.   In all these cases, subsequent to the detection of the pathogen, infected plant shipments/nursery stock were either destroyed or rejected from entering California. The presence and status of anthracnose disease caused by C. aracearum in Guatemala and Costa Rica have not been reported.

Hosts: Aglaonema sp. (Chinese evergreen), Cymbidium sp. (orchid), Dieffenbachia sp. (CDFA detection records 2015-2017), Monstera deliciosa (Swiss cheese plant/tarovine/windowleaf), Philodendron selloum (cut-leaf philodendron) (Farr & Rossman, 2016; Hou et al., 2016).

Symptoms:  Generally, Colletotrichum-infected host plants exhibit symptoms of anthracnose which include dark brown leaf, stem, and fruit spots or lesions, fruit rot, and wilting of leaves which often result in dieback and reduction in plant quality.

Damage Potential:  Anthracnose disease caused by Colletotrichum aracearum can result in reduced plant quality and growth, fruit production and marketability.   Estimates of yield/crop loss due to this pathogen have not been reported. However, in California, nursery and greenhouse production of orchids, Chinese evergreen, dieffenbachia, and other host plants are particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species.  In California’s cultivated fields, disease development may be sporadic as it is affected by levels of pathogen inoculum and environmental conditions.

Disease Cycle:  It is likely that Colletotrichum aracearum has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on plant residue in soil, on infected plants, and on seeds.  During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers.   Conidia are transmitted to host plants.  Humid, wet, rainy weather is necessary for infection to occur.  These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem under controlled environments of greenhouses.  Conidia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue.

Transmission:  Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution: Asia: China; North America: USA (Farr & Rossman, 2017; Hou et al., 2016).  Currently, in the USA, C. aracearum has only been reported from California.

Official Control:  In California C. aracearum is an actionable, Q-rated pathogen, and infected plant material is subject to destruction or rejection.  Colletotrichum aracearum is reportable to the USDA.

California Distribution: San Diego County (see “Background”).

California Interceptions:  During 2015-17, four shipments of Colletotrichum aracearum-infected Aglaonema sp. (Chinese evergreen) cuttings and one of Cymbidium sp. were intercepted in California.  The shipments had originated Guatemala, Costa Rica, and China (see ‘Background’ and ‘Initiating Event’.).

The risk Colletotrichum aracearum would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Similar to other species of Colletotrichum, aracearum requires humid, wet, rainy weather for conidia to infect host plants. This environmental requirement may limit the ability of the pathogen to fully establish and spread under dry field conditions in California

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Presently, the host range of Colletotrichum aracearum is limited to few nursery ornamental plant species belonging to the family Araceae.

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential:  The pathogen has high reproductive potential and conidia are produced successively.  They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Under suitable, wet climates, the pathogen could lower plant growth, fruit production and value and trigger the loss of markets. Nursery-grown orchids and other ornamental host plants could be negatively affected.

Evaluate the economic impact of the pest to California using the criteria below.

Score: A, B, C

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: The pathogen could significantly impact cultural practices or home garden plantings.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Colletotrichum aracearum: Medium (11)

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Colletotrichum aracearum to California = (11).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Low (-1) – Colletotrichum aracearum was detected in a nursery in San Diego County.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 10.

Uncertainty:

The host range of Colletotrichum aracearum is presently limited to few plants in Araceae.  Further host range studies are needed.  Also, results of detection surveys for C. aracearum in nursery, commercial, and natural environments within California may alter its proposed rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose pathogen, Colletotrichum aracearum is B.

References:

Farr, D. F., & A. Y. Rossman.  2016.  Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Retrieved April 3, 2016, from

http://nt.ars-grin.gov/fungaldatabases/

Hou, L.W., F. Liu, W. J. Duan, and L. Cai. 2016. Colletotrichum aracearum and C. camelliae-japonicae, two holomorphic new species from China and Japan. Mycosphere 7(8): 1111-1123.

Kennedy, A.  2017.  Email from A. H. Kennedy, Molecular Biologist, National Identification Services, USDA APHIS PPQ PM to John Chitambar, CDFA, sent: August 29, 2017, 12:54 pm.

Latham, S.  2017.  Email from A. H. Kennedy, Molecular Biologist, National Identification Services, USDA APHIS PPQ PM to Suzanne Latham, CDFA, sent: August 18, 2017, 12:11 pm.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

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Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Plasmopara constantinescui Voglmayr & Thines 2007

California Pest Rating for
Plasmopara constantinescui Voglmayr & Thines 2007
Pest Rating: B
PEST RATING PROFILE

Initiating Event:

On August 8, 2017, diseased leaves of Impatiens walleriana plants were collected, from a retail nursery in Placer County, by Placer Agricultural County officials and sent to the CDFA Plant Pathology Laboratory for diagnoses.  The plants had been shipped from a different nursery in San Joaquin County.  Cheryl Blomquist, CDFA plant pathologist, identified the downy mildew pathogen, Plasmopara constantinescui, as the cause for the disease.  The pathogen was assigned a temporary ‘Q’ rating.  Consequently, the infected plants, received at Placer County, will be destroyed by County officials (Walber, 2017).  Impatiens walleriana plants related to the shipment from San Joaquin County were double-bagged and disposed at a landfill, by the nursery (Khan, 2017).  The risk of introduction and establishment of this pathogen in California is assessed and a permanent rating is herein proposed.

History & Status:

Background:   Plasmopara constantinescui is an obligate oomycete plant pathogen that causes downy mildew disease in its host plants.  Presently, the host range for the pathogen only includes Impatiens species, belonging to the plant family Balsaminaceae.

Plasmopara constantinescui was originally described as Bremiella sphaerosperma from Impatiens in eastern Russia and northeastern North America (Constantinescu, 1991).  However, after molecular phylogenetic analyses of DNA sequences, B. sphaerosperma was found to belong to the genus Plasmopara and transferred there accordingly.  Furthermore, as there already existed, within Plasmopara, a species by the same epithet, the newly-transferred pathogen was given a new epithet, P. constantinescui (Voglmayr & Thines, 2007).  This species was also shown to be closely related to Plasmopara obducens, which is a common, widely distributed pathogen of several species of Impatiens in the Northern Hemisphere, including California (Constantinescu, 1991; Voglmayr & Thines, 2007).

Hosts:  Impatiens sp. (impatiens), I. capensis (jewel weed), I. noli-tangere (western touch-me-not), I. pallida (pale touch-me-not) (Constantinescu, 1991; Farr & Rossman, 2017).  Plasmopara constantinescui was recently detected in Impatiens walleriana (buzzy lizzy) plants (see: ‘Initiating Event’.) 

Symptoms:  Pale yellowish to ochre, round to irregular, and scattered spots appear on the upper surface of leaves.  These spots are small (1-6 mm-diam.), vein-limited, and with margins that are indistinct to reddish brown or violaceous.  They rarely coalesce and cover larger areas.  White to greyish or yellowish downy growth of sporangiophores of the oomycete develop in patches on the underside of the spots (Constantinescu, 1991).  It is likely that, similar to other downy mildew-causing pathogens, Plasmopara constantinescui attacks and spreads rapidly in young, tender green leaf, shoot, and blossom tissue (Agrios, 2005).

Disease development: Generally, downy mildew pathogens overwinter as thick-walled resting spores called oospores in plant debris in the soil or on weed hosts, and as mycelium in infected, but not dead, twigs.  Downy mildew develops and is severe under conditions that favor periods of prolonged leaf wetness and high relative humidity during cool or warm, but not hot, periods.  During rainy period in spring, the oospores germinate to produce a sporangium.  The sporangium or its zoospores are transmitted by wind or water to wet leaves near the ground where they infect through stomata of the lower leaf surface.  Mycelium develops and spreads into intercellular spaces of leaves.  When it reaches the sub-stomatal cavity, it forms a cushion from which sporangiophores arise and grow through the stoma.  Sporangia are produced at the tips of the sporangiophores and are transmitted by wind or rain to nearby non-infected plants (Agrios, 2005; Daughtrey et al., 1995).  In pathogenicity tests, Plasmopara constantinescui was able to cause systemic shoot infection of Impatiens walleriana (Personal communication: Suzanne Latham, CDFA plant pathologist).

Dispersal and spread: Wind, rain/water splash, infected plants and infected plant debris.

Damage Potential: While estimates of crop losses caused particularly by Plasmopara constantinescui have not been reported, generally, downy mildews can cause significant losses in short periods of time. Affected plants may result in defoliation, flower drop, and stem rot, similar to Impatiens walleriana plants infected with the closely related downy mildew species, P. obducens (Crouch et al., 2014).  Nurseries, private and public gardens, and landscape plantings may be at particular risk of contracting downy mildew disease caused by P. constantinescui.  Fungicidal control of the pathogen is possible, but may be difficult.  Under cool wet weathers, downy mildews are often uncontrollable and checked only when the weather turns dry and hot (Agrios, 2005).

Worldwide Distribution: Asia: Eastern Russia (formerly USSR); North America: Canada, USA (Indiana, Massachusetts, Wisconsin, Iowa, Maryland, Minnesota, Virginia, South Carolina, and California) (Constantinescu, 1991; Farr & Rossman, 2017; Voglmayr & Thines, 2007; CDFA Pest and Damage Record 2017).

Official Control:  Bremiella sphaerosperma (synonym of Plasmopara constantinescui) is on the ‘Harmful Organism List’ for Brazil (USDA PCIT, 2017).  Presently, P. constantinescui has a Q rating in California.

California Distribution:  Based on the source of diseased Impatiens, Plasmopara constantinescui is present in San Joaquin County

California Interceptions:  One intrastate interception in Placer County (see: Initiating Event).

The risk Plasmopara constantinescui would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: The downy mildew oomycete, Plasmopara constantinescui requires prolonged periods of leaf wetness and high relative humidity during cool or warm, but not hot, periods. These conditions for infection and development of the pathogen is likely to limit its establishment in California, to coastal regions in particular.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: The host range for the pathogen is limited to Impatiens

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Spores are produced in abundance. The pathogen is transmitted via infected plant material, winds, and rain/water splash.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: If left uncontrolled, downy mildews can cause significant losses in short periods of time. Affected plants may result in defoliation, flower drop, and stem rot, thereby lowering crop yield and value in increasing production costs largely due to administration of control measures.  Fungicidal control of the pathogen is possible, but may be difficult.  Under cool wet weathers, downy mildews are often uncontrollable and checked only when the weather turns dry and hot.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C, D.

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score:  3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact:  Downy mildew disease caused by Plasmopara constantinescui could significantly impact home/urban, private and public gardens, and landscape plantings.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Plasmopara constantinescui:

Add up the total score and include it here. 11

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is ‘Low’.  Based on the source of diseased Impatiens, Plasmopara constantinescui is only present in San Joaquin County.

Score: (-1)

-Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 10.

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Plasmopara constantinescui is B.

References:

Agrios, G. N.  2005.  Plant Pathology fifth edition.  Elsevier Academic Press, Massachusetts, USA.  922 p.

Calflora.  2017.  Information on California plants for education, research and conservation. [web application]. 2017. Berkeley, California. The Calflora Database [a non-profit organization].  http://www.calflora.org/

Constantinescu, O. 1991. Bremiella sphaerosperma sp. nov. and Plasmopara borreriae comb. nov. Mycologia 83: 473-479.

Crouch, J. A., M. P. Ko, and J. M. McKemy.  2014.  First report of impatiens downy mildew outbreaks caused by Plasmopara obducens through the Hawai’ian Islands.  Plant Disease, 98: 696.  DOI: https://doi.org/10.1094/PDIS-10-13-1017-PDN

Daughtrey, M. L., R. L. Wick, and J. L. Peterson.  1995.  Downey mildews.  Part I. infectious diseases, diseases caused by fungi.  Compendium of flowering potted plant diseases.  APS Press, the American Phytopathological Society.  38-38 p.

Farr, D. F., and A. Y. Rossman.  2017.  Fungal Databases, U. S. National Fungus Collections, ARS, USDA. Retrieved September 7, 2017, from http://nt.ars-grin.gov/fungaldatabases/

French, A. M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento (Updated online version by T. Tidwell, May 2, 2017).

Khan, S.  2017.  Email from S. Khan, CDFA Pest Exclusion, to T. Walber, CDFA Interior Pest Exclusion, and J. Chitambar, CDFA, dated 9/19/2017. 4:43 pm.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved September 7, 2017. 4:19:24 pm CDT.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Voglmayr, H., and M. Thines.  2007.  Phylogenetic relationships and nomenclature of Bremiella sphaerosperma (Chromista, Peronosporales). Mycotaxon 100: 11-20.

Walber, T.  2017.  Email from T. Walber, CDFA Interior Pest Exclusion, to J. Chitambar, CDFA, dated 9/8/2017, 9:44 am.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Phytophthora cactorum (Lebert & Cohn) J. Schröt. 1886

2 Comments
California Pest Rating Proposal for
Phytophthora cactorum (Lebert & Cohn) J. Schröt. 1886
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

None.  The current risk and status of Phytophthora cactorum in California are reassessed and a permanent rating is proposed.

History & Status:

Background:  Phytophthora cactorum is an oomycete pathogen that has a very wide host range and can cause a wide range of disease symptoms including, root rot, collar and crown rot, fruit rot, and stem canker, usually in conjunction with other Phytophthora spp. in its hosts.  Phytophthora root and crown rot disease are among the most important soilborne diseases of stone fruits (Brown & Mircetich, 1995).  It is widespread in temperate regions of all continents and occurs in soils of natural forests, agricultural fields and orchards.  It can persist and spread in different environments and is capable of surviving in the soil as a saprophyte and by producing resting spores.

Phytophthora cactorum is widespread in California and has been found in several counties (see: “California Distribution”).  In California, P. cactorum has been found in several hosts: apple, avocado, apricot, American plum, European plum, Japanese plum, Myrobalan plum, sour cherry, sweet cherry, sweet almond, Mabaleb cherry, cherry laurel, peach, nectarine, pear, Southern California walnut, Northern California walnut, English walnut, strawberry, oval kumquat, sweet orange, kiwifruit, peony, rose, rhodendron, tomato, garden rhubarb, lilac, lily, calla lily, Didier’s tulip, tulip, garden snapdragon, western vervain, virbinum, blue blossom ceanothus, million bells, safflower, wild oats, daphne, white fir, Pacific madrone, chamise, manzanita, wild oats, coyote brush, incense cedar, beefwood, deodar cedar, eucalyptus, California buckthorn/coffeeberry, buckthorn, California flannelbush, toyon, common hop, holly, spicebush, carob, savin juniper, juniper, English laurel, redbay, Frasier’s photinia, chokeberry, Ponderosa pine, sticky cinquefoil, Formosa fire thorn, fire thorn, California live oak, valley oak, oak, cork oak, southern live oak, Indian hawthorn, redwood, giant sequoia, yew, and sticky monkey flower (French, 1989, CDFA Pest Damage Records).  The pathogen has also been recovered from various habitats including flowing water, stream and ditch banks, residential and public gardens, recreational areas, orchards, forests, and nurseries (Yakabe et al., 2009; CDFA Pest Damage Records).

Hosts: Phytophthora cactorum has a very wide host range of plants belonging to several families including, Aceraceae, Apocynaceae, Apiaceae, Araliaceae, Cactaceae, Cucurbitaceae, Cornaceae, Ebenaceae, Ericaceae, Fagaceae, Geraniaceae, Grossulariaceae, Hippocastanaceae, Juglandaceae, Lauraceae, Liliaceae, Oleaceae, Pinaceae, Proteaceae, Polygonaceae, Rutaceae, Rosaceae, Salicaceae, Solanaceae, Sterculiaceae, and Violaceae (CABI, 2017).

Farr and Rossman (2017) include 1332 records of hosts for Phytophthora cactorum and its synonyms.  Hosts include: Abies alba (silver fir), A. amabilis (Pacific silver fir), A. balsamea (balsam fir), A. balsamea var. phanerolepsis, A. concolor (white fir), A. firma (momi fir), A. fraseri (Fraser fir), A. magnifica var. shastensis (Shasta red fir), A. procera (noble fir), Abies sp., Acacia sp. (wattles/acacias), Acer spp. (maples), Actinidia chinensis (kiwi), A. deliciosa (fuzzy kiwifruit), Adenostoma fasciculatum (chamise), Aesculus hippocastanum (horse chestnut), Aesculus sp. (buckeye and horse chestnuts), Agonis flexuosa (Jervis Bay Afterdark), Alnus glutinosa (common alder/black alder), A. incana (grey alder/speckled alder), A. oregana (Oregon alder), Amygdalus persica (peach), Ananas comosus (pineapple), Anemone coronaria (poppy anemone/Spanish marigold), Angelica sp. (angelica), Annona cherimola (cherimoya), Antirrhinum sp., A. majus (snapdragon), Aquilegia sp. (columbine), Aralia cordata (spikenard), A. elata (Japanese angelica-tree), Arbutus menziesii (Pacific madrone/madrone), Arctostaphylos spp. (manzanita), Aster spp. (asters), Aucuba japonica (spotted laurel/Japanese laurel), Avena fatua (common wild oat), Baccharis pilularis (coyote brush),  Banksia spp. (banksia), Begonia sp. (begonia), Beta vulgaris var. crassa (beets), Betula lutea (yellow birch), B. pendula (silver birch), Betula sp. (birch), Boehmeria spp. (false nettles), Brassica oleracea var. bullata (Brussel sprouts), Brassica sp. (mustard), Brassolaeliocattleya sp. (orchid), Bryophyllum pinnatum (airplant), Buxus sp. (boxwood), Cactus sp., Calceolaria integrifolia (bush slipperwort), Calceolaria sp. (sweetshrub), Calibrachoa sp. (million bells), Callistephus chinensis (China aster), Calocedrus decurrens (California incense cedar), Calycanthus floridus (eastern sweetshrub), C. occidentalis (spicebush), Calytrix angulata (yellow starflower), Capsicum annuum (cayenne pepper), C. frutescens (chili pepper), Carica papaya (papaya), Carthamus tinctorius (safflower), Carya illinoinensis (pecan), Castanea sativa (sweet chestnut), Castanea sp., Casuarina sp. (beefwood), Catharanthus roseus (Madagascar periwinkle), Ceratonia siliqua (carob), Cereus spp., Cattleya sp. (cattleya orchid), Ceanothus thyrsiflorus (blue blossom ceanothus), Cedrus deodara (deodar cedar), Ceratonia siliqua (carob tree),  Chamaecyparis spp. (false cypress), Chrysalidocarpus lutescens (areca palm/butterfly palm), Chrysanthemum spp., Citrullus lanatus (watermelon; syn. C. vulgaris), Citrus aurantium (bitter orange), C. grandis (pomelo; syn. C. maxima), C. limon (lemon), C. limonia (Mandarin lime), C. sinensis (sweet orange), Citrus sp., Clarkia spp., Cleome spp.,  Cocos nucifera (coconut), Cornus sp. (dogwood), C. sericea (western dogwood), Cucumis  melo var. inodorus (Kolkhoznitsa melon), C. melo var. reticulatus (galia melon), C. sativus (cucumber), C. pepo (field pumpkin), Dahlia sp., Daphne cneorum (rose daphne/garden flower), D. mezereum (February daphne), D. odora (winter daphne), Daphne sp., Dendrobium sp. (dendrobium orchid), Dianthus caryophyllus (carnation), Daucus carota (carrot), Diospyros kaki (persimmon), Diplacus aurantiacus (syn. Mimulus aurantiacus, sticky monkeyflower), Eriobotrya japonica (loquat), Echinochloa crus–galli (barnyardgrass), E. eyriesii, Epidendrum spp. (Epidendrum orchids), Erica hyemalis (cape heath), Eucalyptus spp., Fagus sp. (beeches) F. sylvatica (common beech), Fragaria spp. (strawberry), F. ananassa (strawberry), F. chiloensis (Chilean strawberry), F. vesca (wild strawberry), Frangula californica (coffeeberry/California buckthorn), Fraxinus spp., (ash), Fremontia californica (California flannelbush; syn. Fremontodendron californicum (California flannelbush), Fremontia sp., F. mexicanum (Mexican flannelbush), Fortunella margarita (oval kumquat), Galeandra baueri (orchid), Gladiolus sp., Glycine max (soybean), Hesperocyparis macrocarpa (syn. Cupressus macrocarpa, Monterey cypress), Heteromeles arbutifolia (toyon), Hibiscus spp. (rosemallows), Humulus lupulus (common hop), Ilex sp. (holly), Juglans californica (California black walnut), J. hindsii (Northern California walnut/Hinds’ black walnut), J. nigra (black walnut), J. pyriformis, J. regia (English walnut), Juglans sp., Juniperus procera (African juniper), J. sabina (savin juniper), Juglans. sp., Kalanchoe spp., Lactuca sativa (lettuce), Laeliocattleya sp. (orchid), Lilium spp. (lily), Lycopersicon esculentus (tomato; syn.  Solanum lycopersicum), Malus domestica (apple), Malus sp., M. sylvestris (European crab apple), Mespilus germanica (medlar), Panax quinquefolius (American ginseng), Pelargonium spp. (pelargonium), Paeonia lactiflora (Chinese peony/common garden peony), Paeonia spp. (peony), Panax spp. (ginseng), Persea americana (avocado), P. borbonia (redbay), Photinia spp. (photonia/chokeberry), Picea spp. (spruce), Pinus spp. (pine), Populus alba (silver-leaf poplar), Potentilla glandulosa (syn. Drymocallis glandulosa, sticky cinquefoil), Prunus armeniaca (apricot/American plum), P. avium (sweet cherry), P. cerasus (sour cherry), P. dulcis (almond; syn. P. amygdalus), P. ilicifolia (hollyleaf cherry/evergreen cherry), P. laurocerasus (cherry laurel/English laurel), P. mahaleb (mahaleb cherry), P. mume (Chinese plum/Japanese apricot), P. persica (peach), P. persica var. nucipersica (nectarine), P. salicina (Japanese plum), Prunus sp., Pyracantha coccinea (scarlet firethorn), , P. koidzumii (Formosa firethorn), Pyracantha sp. (fire thorn), Pyrus communis (European pear), Quercus agrifolia (California live oak/coast live oak), Q. falcata (southern red oak), Q. lobata (valley oak), Q. petraea (durmast oak), Q. robur, (English oak), Quercus sp., Q. suber (cork oak), Q. virginiana (live oak), Rhamnus (Frangula) californica (California coffeeberry), Rhaphiolepis indica (Indian hawthorn), Rheum rhaponticum (false rhubarb), Rheum hybridium (rhubarb), Rhododendron spp., (azalea), Ribes spp., (currants), R. lobbii (Lobbs gooseberry), R. uva-crispa (gooseberry), Rosa sp. (rose), Salix sp. ( willow), Sequoiadendron giganteum (giant sequoia), Solanum (nightshade), S. lycopersicum (tomato), Syringa vulgaris (lilac), Syringa sp., Taxus sp. (yew), Theobroma cacao (cocoa), Tulipa sp. (tulip), Tulipa gesneriana (Didier’s tulip), Viola sp. (violet), Vanda sp. (Vanda orchid), Verbena sp., V. lasiostachys (western vervain), Viburnum spp., Vicia faba (fava bean/broad bean), Vicia sp. (vetch), V. unguiculata, Vigna unguiculata (cowpea; syn. V. sinensis), V. cylindrica (catjang), V. sesquipedalis (yardlong bean), Vitis vinifera (grape ), Zea mays (corn), Zantedeschia sp. (calla lily) (CABI, 2017; Farr & Rossman, 2017; French, 1989; CDFA Pest Damage Records).

Symptoms: Phytophthora cactorum attacks a wide range of host plants causing varied symptoms, depending on the host.  Symptoms include root rot, collar and crown rot, fruit rot, stem cankers, leaf blight, wilts and seedling blights.  This pathogen can cause pre- and post-emergence damping-off disease in several plant species.  It has been reported to reduce sprouting and kill seedlings of beech, and cause seedling blight in Pinus spp., Salix scoulerana, and Robinia spp. (CABI, 2017).

On apple, pear and other woody hosts, P. cactorum causes crown, collar and root rot.  Crown rot affects rootstock tissue from the graft union down to the tips of the primary roots, whereas collar rot affects the scion above the graft union or slightly above the soil line.  Root rot refers to symptoms that appear beyond the proximal junction of primary roots to crown tissue (Cox, 2014).   Above ground symptoms are indicative of an impaired root system and include general stunting with reduced terminal growth and small, chlorotic leaves.  Symptom expression depends on the amount of infected crown or root tissue and their rate of destruction.  Young trees are usually killed by the pathogen since their root systems and crown regions are not as developed as those of mature trees.  Generally, crown rots advance rapidly and trees fall and die soon after the first warm spring.  Their leaves wilt, dry, and remain attached to the tree (Adaskaveg et al., 2009; Gubler & Teviotdale, 2009).  Trees with root rot slowly decline and eventually die over several seasons. At early stages of tree decline, removing the bark reveals orange to reddish brown necrotic lesions in cambium tissue.  A thin, dark delineated margin is evident at the junction of healthy tissue and the expanding lesion which, over time, turns dark brown as it gets colonized by secondary fungi and bacteria.  Symptoms can extend through the root system resulting in a lack of fibrous and feeder roots.  Crown lesions can extend to the primary roots and up to the graft union, while collar lesions can extend up to a meter up from the graft union.  On dissection, collar infections may appear striped in the inner phloem tissue and, sometimes, result in weeping though cracked barked tissue (Cox, 2014).   Phytophthora cactorum also causes fruit rot in apple and pear, producing pale olive and dark brown lesions in apple and pear respectively.  Those lesions are diffusely marbled or uniformly colored with softly delineated margins (Covey et al., 2014).

In Rhododendrons affected by Phytophthora root rot, roots become necrotic and leaves turn chlorotic, wilt, roll downwards parallel to the midrib, and eventually turn brown.  In contrast, leaves of infected azalea become chlorotic, and then necrotic, but seldom wilt. Necrotic leaves eventually drop to the ground (Hoitink et al., 2014).

Infected trees may develop cankers on the stem or near the soil line with discoloration of infected bark, sometimes extending into the internal tissues (CABI, 2017).

Phytophthora cactorum can cause crown rot and root rot of strawberries.  Initial symptoms typically include plant stunting and small leaves.  Later, infected plants may collapse rapidly or gradually.  When cut open, brown discoloration of the crown vascular tissue or entire tissue is apparent.  While other Phytophthora species may be involved, P. cactorum is the most common species on strawberry (Koike et al., 2008).  Fruit is also infected by P. cactorum resulting in leather rot disease.  On green fruit, symptoms appear as dark brown areas or green areas with brown margins.  As the rot spreads, the entire fruit turns brown with a rough texture that appears leathery. Infected mature fruit may be slightly discolored or turn brown to dark purple.  Internally, vascular tissue to each seed is darkened, and in later stages of decay mature fruit becomes leathery.  Infected fruit have unpleasant odor and taste.  Under moist conditions, white mycelial growth may be present on the surface of fruit.  Green and mature fruit eventually become shriveled mummies (Ellis & Madden, 1998).

Disease development: P. cactorum can survive for several years, mainly as oospores (sexual spores) in soil and mummified fruit. The pathogen can also survive as chlamydospores (thick-walled asexual spores) (Erwin & Ribeiro, 1996) in orchard soil or mycelium in host tissue (Cox, 2014).  Similar to other Phytophthora spp., P. cactorum lives as a saprophyte in litter and in soil containing dead organic material and is favored by moist and moderate climates. In spring, and in saturated soil, oospores germinate to produce sporangia.  In free water, zoospores are produced within sporangia and liberated into water.  While oospores and chlamydospores form the primary inoculum, sporangia are the principal source of secondary inoculum (CABI, 2017).  Free water is required for infection, however, a high incidence of disease can occur with as little as 2 hours or less of wetness at 17-25°C.  Optimum temperature for infection is 21°C.   The most favorable temperatures for sporangia production are between 15 and 25°C, and optimally at 20°C.  No sporangia are produced at 10 and 30°C (Ellis & Madden, 1998).   Sporangia can germinate directly or indirectly by producing zoospores.  Zoospores allow a population to increase rapidly and disperse widely in films of free water.  Zoospores are expelled from sporangia under suitable temperature and moisture conditions and swim by means of their flagella towards their host in response to root exudates.  Once a zoospore comes in contact with a root it germinates producing a germ tube which penetrates the root directly under waterlogged soil conditions.   More mycelium develops and eventually, oospores (sexual spores) are produced and serve as resting structures that can survive for several years.  (CABI, 2017).

Transmission: Like most Phytophthora species, P. cactorum is soil-borne and water-borne and may be spread to non-infected sites through infected plants, nursery and planting stock, and seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment, tools, and boots.  Under high moisture and windy conditions, sporangia may be airborne and important in spread of diseases such as leather rot of strawberry.  The pathogen is not seed-borne but can be spread by infected seedlings and through soil or plant debris containing oospores or chlamydospores contaminating seed samples (CABI, 2017).  Furthermore, irrigation water from canals, rivers, and ponds can be contaminated with Phytophthora spp. (Brown & Mircetich, 1995).

Damage Potential: Specific crop losses caused by Phytophthora cactorum alone may be difficult to assess as more than one species of Phytophthora may cause diseases with symptoms similar to those caused by P. cactorum and may be present in infected hosts. Nevertheless, P. cactorum is a serious pathogen of a wide range of plant species. Infections of 88-97% apple and pear nursery stock material in commercial nurseries has been reported (Jeffers & Aldwinckle, 1988), and P. cactorum has been frequently detected in several ornamental nurseries within California (Yakabe et al., 2009).  Therefore, nurseries may be at risk and need to be monitored for this pathogen to ensure production and planting of disease-free nursery stock.

California’s native vegetation is also at risk of root and crown rot caused by P. cactorum and other Phytophthora spp., many of which are endemic (limited) to California, while some are rare, endangered, or threatened plants, e.g., Ribes spp. (currant/gooseberry), Monterey cypress, and Arctostaphylos spp. (manzanita) (Calflora, 2017; CNPS, 2017).  Introduction of Phytophthora species are a threat to plant health in Bay Area restoration sites, where nursery stock is planted for flood control or to mitigate environmental impacts.   Detections on madrone, toyon, oaks, sticky monkeyflower, and manzanitas in native stands indicate that P. cactorum is capable of becoming established in a variety of native plant habitats under a range of soil and environmental conditions and can have negative impacts on native vegetation.

Worldwide Distribution: Asia: China, India, Indonesia, Iran, Israel, Japan, Korea DPR, Republic of Korea, Laos, Lebanon, Malaysia, Pakistan, Philippines, Taiwan, Turkey, Vietnam; Africa: Egypt, Kenya, Morocco, Senegal, South Africa, Tunisia, Zimbabwe; North America: Bermuda, Canada, Mexico, USA; South America: Argentina, Brazil, Chile, Colombia, Peru, Uruguay, Venezuela; Europe: Austria, Belgium, Bulgaria, Croatia, Czech Republic, (former) Czechoslovakia, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, Netherlands, Norway, Poland, Romania, Russian Federation, Russia (European), Serbia, Slovenia, Spain, Sweden, Switzerland, United Kingdom; Oceania: Australia, New Zealand; Central America and Caribbean: Cuba, El Salvador, Trinidad and Tobago (CABI, 2017; EPPO, 2017).

In the USA, Phytophthora cactorum has been reported from California, Florida, Maine, Michigan, Minnesota, New York, North Carolina, Ohio, South Carolina, Tennessee, Virginia, Washington (CABI, 2017; EPPO, 2017).

Official Control:  Presently, Phytophthora cactorum is the “Harmful Organism Lists” for Egypt, French Polynesia, Guatemala, India, Israel, Lebanon, and Nicaragua, while, Phytophthora spp. is on the “Harmful Organism Lists” for Canada, French Polynesia, Mexico, Namibia, Seychelles, South Africa, and the Bolivarian Republic of Venezuela (USDA PCIT, 2017).

California Distribution: Phytophthora cactorum is widely distributed within California.  From 2001-July, 2017, the pathogen was detected in Alameda, Butte, Contra Costa, Imperial, Los Angeles, Marin, Merced, Monterey, Placer, Sacramento, San Diego, San Francisco, San Mateo, Santa Barbara, Santa Clara, Santa Cruz, Siskiyou, Solano, Sonoma, and Stanislaus Counties (CDFA Pest Damage Records).

California Interceptions:  None reported.

The risk Phytophthora cactorum would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Phytophthora cactorum has already established a large distribution under moist and cool to warm climates in California.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: The pathogen has a very wide host range.

Evaluate the host range of the pest.

Score: 3

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Phytophthora cactorum, like other Phytophthora, has high reproductive capability under moist conditions.  It is dependent on moisture for spore dissemination and plant infection.  It is soilborne and may be spread to non-infected sites through infected plants, nursery and planting stock, and seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment, tools, boots, rivers, canals, and ponds.  Therefore, it is given a high rating in this category.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential. 

4) Economic Impact: Damage caused by Phytophthora cactorum alone may be difficult to assess as more than one species of Phytophthora may be associated with root and crown rot of host tree.  Nevertheless, cactorum is a serious pathogen affecting production of several economically important hosts including, apple, pear, stone fruits, strawberry, ornamentals, and California native plants.  Nursery productions could be at risk. Controlling the disease would include soil water management and use of resistant varieties, thereby requiring changes in cultural practices and increase in crop production costs.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, D, G

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: In conjunction with other Phytophthora, P cactorum may be a contributor to root and crown disease of environmental plants. California’s native vegetation is at risk of root and crown rot damage caused by P. cactorum and other Phytophthora spp.  Certain native plants are endemic (limited) to the State, while some are rare, endangered, or threatened.  The pathogen is capable of becoming established in a variety of native plant habitats under a range of soil and environmental conditions and can have negative impacts on native vegetation.  Its association alone and with other Phytophthora spp. in infected forest and native tree and shrub hosts could result in lowered biodiversity, disrupted natural communities, and critical habitats.  Also, it may significantly impact ornamental plantings and home/urban gardening.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: A, B, C, E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 3

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Phytophthora cactorum:

Add up the total score and include it here. 14

-Low = 5-8 points

-Medium = 9-12 points

                        –High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is:

Score: (-3)

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

 Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Phytophthora cactorum is B.

References:

Adaskaveg, J. E., J. L. Caprile, W. D. Gubler, B. L. Teviotdale.  2009.  Cherry: Phytophthora root and crown rot, pathogen: Phytophthora spp.  UCIPM Statewide Integrated Pest Management Program, University of California Agriculture & Natural Resources.  http://ipm.ucanr.edu/PMG/r105100711.html

Browne, G. T., and S. M. Mircetich.  1995.  Phytophthora root and crown rots.  In Compendium of Stone Fruit Diseases, Eds: J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu, and J. K. Uyemoto.  APS Press, The American Phytopathological Society. Pages 38-40.

CABI.  2017.  Phytophthora cactorum (apple collar rot) full datasheet.  Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/40953

Calflora.  2017.  Information on California plants for education, research and conservation. [Web application]. 2017. Berkeley, California. The Calflora Database [a non-profit organization].  http://www.calflora.org/

CNPS.  2017.  Inventory of rare and endangered plants of California (online edition, v8-03 0.38).  California Native Plant Society, Rare Plant Program. Website http://www.rareplants.cnps.org [accessed 10 August 2017].

Covey, R. P. Jr., and D. C. Harris; revised by K. Cox.  2014.  Phytophthora fruit rot.  In Compendium of Apple and Pear Diseases and Pests Second Edition Eds. T. B. Sutton, H. S. Aldwinckle, A. M. Agnello, J. F. Walgenbach.  APS Press, The American Phytopathological Society.  Pages 41-42.

Cox, K.  2014.  Phytophthora collar, crown, and root rots.  In Compendium of Apple and Pear Disease and Pests Second Edition Eds: T. B. Sutton, H. S. Aldwinckle, A. M. Agnello, J. F. Walgenbach.  Pages 63-65.

EPPO.   2017.   Phytophthora cactorum (PHYTCC).  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  https://gd.eppo.int/

Ellis, M. A., and L. V. Madden.  1998.  Leather rot.  In Compendium of Strawberry Diseases Second Edition Ed. J. L. Maas.  APS Press, The American Phytopathological Society.  Pages 33-35.

Erwin, D. C., and O. K. Ribeiro.  1996.  Phytophthora Diseases Worldwide. St Paul, Minnesota, USA: American Phytopathological Society Press.

Farr, D. F., and A. Y. Rossman.  2017.  Fungal Databases, U.S. National Fungus Collections, ARS, USDA. Retrieved July 31, 2017, from https://nt.ars-grin.gov/fungaldatabases/

French, A.M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento (Updated online version by T. Tidwell, May 2, 2017).

Gubler, W. D., and B. L. Teviotdale.  2009.  Apple, Phytophthora root and crown rot (updated 3/2009).  UCIPM, University of California Agriculture & Natural Resources, Statewide Integrated Pest Management Program.  http://ipm.ucanr.edu/PMG/r4100511.html

Hoitink, D. M. Benson, and A. F. Schmitthenner; revised by D. M. Benson and S. N. Jeffers.  2014.  Phytophthora root rot.  In Compendium of Rhododendron and Azalea Diseases and Pests Second Edition Eds: R. G. Linderman and D. M. Benson.  Pages 5-10.

Jeffers, S. N., and H. S. Aldwinckle.  1988.  Phytophthora crown rot of apple trees: sources of Phytophthora cactorum and P. cambivora as primary inoculum. Phytopathology, 78: 328-335

Mircetich, S. M., and M. E. Matherton.  1976.  Phytophthora root and crown rot of cherry trees.   Phytopathology 66: 549-558.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved June 6, 2017. 11:48:29 am CDT.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Yakabe, L. E., C. L. Blomquist, S. L. Thomas, and J. D. MacDonald.  2009.  Identification and frequency of Phytophthora species associated with foliar diseases in California ornamental nurseries.  Plant Disease, 93: 883-890.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

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 PEST RATING: B

Posted by ls

Fungi, Plant Pathogens

Uromyces transversalis

California Pest Rating for
Uromyces transversalis (Thüm.) G. Winter
Pest Rating: C
PEST RATING PROFILE
Initiating Event:  

None.  The status of Uromyces transversalis in California, is updated and the current rating is reviewed.

History & Status:

Background:  Uromyces transversalis is an autoecious rust pathogen that causes rust disease, commonly known as gladiolus rust, only in members of the family Iridaceae, including Gladiolus, Tritonia, Crocosmia, and Watsonia spp.  Gladiolus is the major host of the pathogen, while the other hosts are of lesser economic importance.  Of six rust pathogens that can infect gladiolus, U. transversalis is the most economically damaging one.

Uromyces transversalis is indigenous to eastern and southern Africa, where it was first detected on leaves of Tritonia securigera in 1876.  Almost a century later, the pathogen spread to the Mediterranean region and southern Europe.  During the 1960-70s it was reported from France, Italy, and Morocco, and from England by 1996 (USDA APHIS PPQ, 2007).

Gladiolus rust was first detected and confirmed in the United States in April 2006, from a gladiolus production farm in Manatee County, Florida, and later, in another commercial gladiolus farm in Hendry County, Florida (USDA APHIS PPQ, 2007).  Then, in May 2006, gladiolus rust was detected on hybrid gladiolus plants in a home garden in San Diego, California.  Consequently, an intensive 23 square mile survey was conducted and the rust pathogen was detected at one commercial nursery and two other residential sites (Blomquist et al., 2007).  Since 2006, the pathogen has been repeatedly detected in Florida and California.  The source of introduction of Uromyces transversalis into the USA is unknown.  The pathogen is known to occur in Mexico and has been intercepted in numerous shipments of cut flowers from Mexico dating back to 2004.  The initial detection in Florida was the result of trace-back investigations following an interception of rust-infected flowers in Hawaii that originated in Florida.  Infected Florida-produced gladiolus flowers were intercepted in Minnesota in 2008, which had, likewise, originated from one of the original infected Florida gladiolus producers (Preston, 2009).

In California, to date, the disease has been detected in over 680 samples submitted to the CDFA Plant Pest Diagnostics Laboratory.  Samples have come primarily from landscapes associated with residences, businesses, and municipalities from no fewer than twelve California counties, ranging from Solano County and San Francisco County in the northern region to San Diego County in the southern region where it was originally detected.  Samples have come from no fewer than 38 different California cities (CDFA Pest Detection Reports).  The wide distribution indicates that Gladiolus Rust is well beyond the possibility of eradication in California, and is, instead, a management issue.

In August 2006, the gladiolus rust pathogen, Uromyces transversalis, was deemed as actionable and reportable by the USDA.  In 2007, federal and state action was taken in accordance with the USDA APHIS’ ‘Gladiolus Rust National Eradication and Management Plan’ (USDA, 2007), whenever the pathogen was detected in commercial growing areas, domestic commerce, and residential areas.  The decision to go that route was made when the pathogen was still believed to be limited in distribution in Florida and California and eradication was thought to be feasible.    However, on May 15, 2015, APHIS revised the domestic response requirements for U. transversalis to no longer take domestic action or require others to take action when gladiolus rust is found in commercial growing areas, domestic commerce, and residential areas.  This revision was made because the pathogen has spread to the limit of its natural range, based on its current distribution, known biology, and plant hardiness zones in the United States.  However, APHIS will continue to regulate other gladiolus rust pathogens that are known to occur in the United States (USDA, 2015).

Transmission:  The primary pathways for introduction of the pathogen are by shipments of infected plants and cut flowers. Interceptions from commercial shipments and passenger baggage at ports-of-entry in Arizona, California, and Texas confirmed that cut flowers are the major pathway of gladiolus rust from other countries (USDA APHIS, 2007). A significant anecdotal observation of the close proximity of residential infections with cemeteries also comes as no surprise, considering the propensity of the public to use gladiolus cut flowers to decorate grave sites.  Long distance and local spread is by wind-blown spores. These airborne spores are easily dispersed by lightly brushing a symptomatic plant and can be spread by surface-contaminated clothing, equipment, corms, rhizomes, and flowers (USDA APHIS PPQ, 2007).

Symptoms: Symptoms are typical for a rust disease, with yellowish-brown (uredinia) or blackish-brown (telia) pustules on the leaves, either solitary or aggregated.  Uredinia develop first and produce urediniospores, followed by development of the telia, which produce teliospores.  Initial symptoms of gladiolus rust are the appearance of small, yellowish spots.  Later, the epidermis bursts open exposing pustules full of yellowish- orange spores.  Over time, pustules coalesce to form large lesions.  Rust pustules normally form on foliage, on both sides, but under heavy disease pressure, can also form on flower spikes. Severely infected plants fail to even flower or produce mature corms. The pustules are formed in lines that run “transversely” across the leaf veins (as opposed to round or amorphous pustules, as is normally the case with most rust fungi on monocots whose sori run longitudinally along the vein of the leaf).  These unique transverse pustules are useful for making field identifications of the rust (USDA, 2007; USDA APHIS PPQ, 2007).

Hosts:  All hosts belong to the family Iridaceae.  The primary/major host is Gladiolus hybrids (sword lily/gladiolus). Minor hosts include, Crocosmia aurea (falling stars), Freesia refracta (common freesia), Tritonia sp. (flame freesia), T. lineata, T. securigera, T. squalida, Watsonia sp. (bugle lily), W. angusta, W. densiflora, W. meriana, and W. borbonica (CABI, 2017; EPPO, 2017; Farr & Rossman, 2017).

Damage Potential:  Gladiolus rust is a serious disease in nurseries and, if left uncontrolled, can completely destroy commercial gladiolus crops.  Severely damaged plants do not flower and/or their corms do not ripen (USDA APHIS PPQ, 2007).  There are efficacious fungicides available that can control the pathogen, however the frequent treatments necessary to protect the product can be costly for producers (Schwartzburg, 2006).  Furthermore, gladiolus rust can be controlled with best management practices (USDA, 2015).

The pathogen has only rarely been found in commercial settings in California, possibly because production managers have taken pro-active measures to protect their crops against the pathogen by frequent scouting and preventive fungicide treatments.  An example of this is a large gladiolus cut flower producer in Santa Barbara County that is virtually surrounded by infected residences. The nursery staff routinely inspect and fungicide-treats the crop which is grown from new imported corms each year.  As further protection, a host-free period at the production grounds follows the harvest of the year’s crop (Scheck, 2012).

Worldwide Distribution: Africa: Kenya, Malawi, Mauritius, South Africa, Tanzania, Uganda, Zambia, Zimbabwe; North America: Mexico, USA (California, Florida); Central America and Caribbean: Costa Rica, Cuba, Martinique; South America: Argentina, Brazil; Europe: France, Italy, Malta, Spain; Oceania: Australia, New Zealand (CABI, 2017; EPPO, 2017; Farr & Rossman, 2017).

Official Control: Uromyces transversalis is on the ‘Harmful Organism Lists’ for the following countries:  Australia, Chile, China, Colombia, Ecuador, French Polynesia, India, Israel, Republic of Korea, Madagascar, Nauru, New Caledonia, Peru, Tunisia (USDA PCIT, 2017).

California Distribution:  Alameda, Contra Costa, Los Angeles, Orange, San Diego, San Francisco, San Mateo, Santa Barbara, Santa Clara, Santa Cruz, Solano, and Ventura Counties.

California Interceptions:  None reported.

The risk Uromyces transversalis would pose to California is evaluated below.

Consequences of Introduction: 

 1) Climate/Host Interaction: The ability for Uromyces transversalis to have suitable hosts and climate in order to establish in California is already illustrated by its state-wide distribution over the past eleven years.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 3

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Gladiolus is the only major host for Uromyces transversalis.

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Uromyces transversalis has high reproduction and dispersal potential.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Gladiolus Rust is known to lower yields, could increase costs due to fungicide treatments for commercial producers, and could result in quarantines by other states or countries.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Gladiolus rust could impact home/urban garden plantings.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Gladiolus Rust:

Add up the total score and include it here. 12

-Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is ‘High’. Gladiolus Rust has spread to at least 12 California counties since its first detection in 2006. 

Score (-3). 

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 9.

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the rating for the gladiolus rust pathogen, Uromyces transversalis, is proposed to continue as C.

References:

Blomquist, C. L., S. L. Thomas, J. M. Mckemy, P. A. Nolan, and M. Luque-Williams.  2007.  First report of Uromyces transversalis, causal agent of gladiolus rust, in San Diego County, California.  Plant Disease, 91: 1202.  http://dx.doi.org/10.1094/PDIS-91-9-1202C

CABI.  2017.  Uromyces transversalis (gladiolus rust) full datasheet.  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/55868

EPPO.  2017.  Uromyces transversalis (UROMTV).  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  https://gd.eppo.int/

Farr, D. F., and A. Y. Rossman. Fungal Databases, U.S. National Fungus Collections, ARS, USDA. Retrieved August 1, 2017, from https://nt.ars-grin.gov/fungaldatabases/

Preston, Catherine (2009) USDA Presentation: Gladiolus Rust, Balancing Eradication Efforts and Growers’ Needs through Regulation. http://dpm.ifas.ufl.edu/plant_pest_risk_assessment/ALS6921%20Presentations/PPQ_GR%20presentation.pdf

Scheck, H.  2012. Communication to Timothy Tidwell, Plant Pathologist, CDFA, from Heather Scheck, Plant Pathologist, Santa Barbara County Department of Agriculture (in 2012).

Schwartzburg, K. 2006. NPAG Report Uromyces transversalis (Thüm.) G. Winter 1884: Gladiolus Rust.

USDA, 2007. Gladiolus Rust (Uromyces transversalis): A National Management Plan for Exclusion and Eradication.  GR Plan Original, February 28, 2007.

USDA.  2015.  APHIS revives response to domestic detections of gladiolus rust caused by Uromyces transversalis.  DA-2015-20, dated May 13, 2015 to State and Territory Agricultural Regulatory Officials.

USDA APHIS PPQ.  2007.  Pest Alert.  Gladiolus rust: a new threat.  United States Department of Agriculture Animal and Plant Health Inspection Service Plant Protection and Quarantine.  APHIS 81-35-011.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System. August 1, 2017, 4:03:49 pm CDT.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Thekopsora minima P. Syd. & Syd. 1915

4 Comments
California Pest Rating for
Thekopsora minima P. Syd. & Syd. 1915
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

On May 2, 2017, a shipment of blueberry (Vaccinium corymbosum) plants showing symptoms of rust were intercepted in San Francisco by San Francisco County Agricultural Officers.  The shipment had originated in Oregon and was destined to a wholesale garden store in San Francisco.  A sample of symptomatic leaves was collected by the County and sent to the CDFA Plant Pathology Lab for diagnosis.  On May 22, 2017, Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen associated with the diseased leaf tissue as Thekopsora minima.  The pathogen was assigned a temporary Q rating.  Subsequently, the consequences of introduction and establishment of T. minima in California are assessed and a permanent rating is proposed herein.

History & Status:

Background: Thekopsora minima is a fungal pathogen that causes rust disease in blueberries, cranberries, rhododendrons, and other plants in the Ericaceae family.  The pathogen completes its life cycle on two different hosts (heteroecious), namely, blueberries and hemlock, and rust disease can lead to extensive defoliation of severely infected plants.

The blueberry leaf rust pathogen was first recorded as endemic in Northeastern America and Japan.  During the past decade, it was introduced on infested Vaccinium corymbosum to other countries including South Africa, Mexico, Australia and Colombia (EPPO, 2016). In the USA, it has been reported mainly from northeastern states and, more recently, from the Western Pacific states of Oregon and California (Wiseman et al., 2016; Shands et al., 2017).

Prior to 1993, taxonomically, Thekopsora minima was generally accepted as a member of a species complex known as Pucciniastrum vaccinii, which was considered the causal agent of blueberry rust.  However, Sato et al., (1993) identified three distinct rust fungi species on Vaccinium spp., of which one of them, namely, T. minina, is pathogenic on blueberry, while the other two species, Naohidemyces vaccinii (formerly P. vaccinii) and N. fujisanensis, were not regarded as pathogens of blueberry, although they infected other Vaccinium species.  Sato et al., (1993) also noted that at that time, T. minima, occurred, in eastern North America and Japan.  Nevertheless, because of the past taxonomic confusion of the species complex, the true global distribution of T. minima may be uncertain as some records attributed to Pucciniastrum vaccinii in Argentina, Hawaii (USA), and Spain may be misidentifications of T. minima (Schrader & Maier, 2015).  Thekopsora minima is also known by its synonyms: Peridermium peckii Thüm, 1880, Uredo minima Schwein, 1922, and Pucciniastrum minimum (Schwein.) Arthur 1906 (Farr & Rossman, 2017).

In California, Naohidemyces vaccinii has been reported on Vaccinium membranaceum (thin leaf huckleberry), V. caespitosum (dwarf bilberry), V. parvifolium (red huckleberry), V. ovatum (California huckleberry), and Vaccinium sp. (French, 1989).  However, recent reports from several states in the US (Oregon and Michigan), China, Mexico, and South Africa, have indicated that Thekopsora minima is the primary pathogen on northern and southern highbush blueberries (Rebollar-Alviter et al., 2011; Shilder & Miles, 2011; Wideman et al., 2016; Zheng et al., 2017).  Rust symptoms have been occasionally observed on various southern highbush blueberry cultivars (Vaccinium corymbosum) within California’s central coastal area, with particular incidences noted in Santa Barbara County in 2010 and 2006 (personal communications: Dr. Timothy D. Miles, Assistant Professor of Plant Pathology, California State University Monterey Bay, and Dr. Janet C. Broome, Global Plant Healthy Senior Manager, Driscoll’s, 2017).  Rust in blueberry was also observed in Ventura County, and has most likely been in the State since the early 2000s (personal communication: Dr. Janet C. Broome, Driscoll’s, 2017). In 2016-2017, rust symptoms, observed on several blueberry plants and cultivars in a field trials in Watsonville, Santa Cruz County, were confirmed by molecular sequencing to be caused by T. minima and marked a first published report of this pathogen in California (Shands, et al., 2017).  On August 9, 2017, in order to officially substantiate the presence of blueberry rust in California, official samples of symptomatic blueberry plant tissue were collected from infected plants in Santa Cruz and Ventura Counties, by the respective County Agricultural officials and submitted to the CDFA Plant Pathology Laboratory for identification of the associated pathogen.  Following morphological and molecular sequence analysis, Cheryl Blomquist, CDFA plant pathologist, confirmed the pathogen to be T. minima.

Disease development: Teliospores of T. minima hibernate on blueberry leaves on the ground and after germination in late spring, infest the alternate host, Tsuga spp., via basidiospores.  Aeciospores are produced and infest Vaccinium and other Ericaceae host plants resulting in the production of urediniospores.  The latter ensure disease spread within the crop during the entire growing season.  Furthermore, it has been shown that other closely related blueberry rust species are capable of surviving as mycelium in plant buds and directly producing urediniospores in spring, thereby eliminating the need of the alternate host (EPPO, 2016).  It is not known if this is the case for T. minima in California where two native host species, Tsuga heterophylla and T. mertensiana can serve as alternate hosts for the pathogen to complete its lifecycle.  These two species are also native to the Pacific western states although the fungus has not been recovered from Tsuga (Wiseman et al., 2016; Shands, et al., 2017).  The other two hemlocks that are alternate hosts, T. canadensis and T. diversifolia, are not generally cultivated in California but may be present in small areas of private production and nurseries.  Pfister et al., 2004, experimentally determined the predicted optimum temperature for urediniospores to be 19.5°C, with a 5% variation in uredinia production between 17.5 and 22°C.

Dispersal and spread: Spores of Thekospora minima are spread over short distances to nearby plants by wind and rain. Spores may also be spread by human contact, clothing, equipment and packaging.  Long distance spread occurs mainly through passage of infected plants including fruit to non-infected regions (EPPO, 2016, Tasmania, 2014).

Hosts: The uredinial and telial stages of the pathogen are found on the main hosts in Vaccinium spp., namely, V. angustifolium var. laevifolium (lowbush blueberry), V. corymbosum (highbush blueberry), V. membranaceum (deciduous huckleberry) and V. erythrocarpum (southern mountain cranberry) in the family Ericaceae.  Other hosts belong to different genera in the same family: Azalea sp., A. pontica var. daviesii, Gaylussacia sp., G. baccata (black huckleberry), Leucothoe sp., Lyonia nezikii, L. ovalifolia var. elliptica, Menziesia sp., Pernettya sp., Pieris sp., Rhododendron nudiflorum, R. ponticum, and Rhodora canadensis.  The aecial stage of the pathogen is found on the alternate host, Tsuga spp., (hemlock; Pinaceae), T. canadensis (eastern hemlock), T. diversifolia (Japanese hemlock), T. heterophylla (western hemlock), T. mertensiana (mountain hemlock) (EPPO, 2016; Farr & Rossman, 2017; Wiseman et al., 2016).

Symptoms: Initial symptoms appear as small yellow, chlorotic leaf spots on upper surfaces of young leaves. As infection progresses these lesions turn rust or brown-colored, enlarge and coalesce covering large areas of a leaf.  On the underside of leaves, small flecks surrounded by water-soaked halos develop turning into yellow-orange, powdery pustules containing uredinia with urediniospores.  Pustules may also develop on blueberry fruit.  In severe infections premature leaf drop and plant defoliation can occur and result in decline in fruit yield and flower production (EPPO, 2016).

Damage Potential: Blueberry rust disease caused by Thekopsora minima may result in plant defoliation and decline in fruit and flower production.  Generally, under conditions of high humidity required for rust fungi infection, significant losses in blueberry production and other Ericaceae host plants can be expected. However, in California, such high humidity climates are not anticipated in blueberry cultivated regions and T. minima has not caused significant rust disease in blueberry, even though it has been in the State for over 17 years ((personal communication: Dr. Janet C. Broome, Driscoll’s, 2017).  Infected plants do not suffer from leaf drop, which is generally associated with the rust, and the pathogen has not been an issue of concern for blueberry growers to warrant administration of control measures.  Some rust disease is apparent on leaves from early spring into summer following periods of significant rain, however, it is difficult to find infected plants later in the season (personal communications: Dr. Janet C. Broome, Driscoll’s, 2017 and Dr. Timothy D. Miles, CSUMB).  Similarly, economic damage to other environmental host plants is expected to be minimal as the pathogen has already been in California for several years without any significant increase of its impact.

Worldwide Distribution: Asia: China, Japan; Africa:  South Africa; Europe: Netherlands (restricted distribution), Portugal (present, few occurrences); North America: Canada, Mexico, USA; South America: Colombia; Oceania: Australia (New South Wales, Queensland, Victoria) (EPPO, 2016, 2017; Mostert et al., 2010; Zheng et al., 2017).

In Europe, the pathogen is currently regarded as “Transient, under eradication” in Belgium and Germany (EPPO, 2017).  In the USA, it has been reported from Delaware, Massachusetts, Michigan, New York and Oregon (EPPO, 2017; Sato et al., 1993; Schilder & Miles, 2011; Wiseman et al., 2016).

Official Control: Thekopsora minima has been on the EPPO Alert List for the European Union since 2016 (EPPO, 2017).  Presently, Thekoposora minima is on the ‘Harmful Organism List” for Peru (USDA PCIT, 2017).

California Distribution: Thekopsora minima has officially been detected in Santa Cruz and Ventura Counties.  The pathogen has also been reported from Santa Barbara County (Shands et al., 2017).

California Interceptions: Thekopsora minima has only been detected once in a shipment of blueberry plants intercepted in San Francisco in 2017 (see “Initiating Event”).

The risk Thekopsora minima would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Main hosts of Thekopsora minima are in the family Ericaceae and include blueberries, rhododendrons and azaleas.  Blueberries are grown in northern coastal and southern coastal regions and in the San Joaquin Valley.  Rhododendrons, azaleas and other horticultural hosts are grown throughout California particularly in coastal climates.  However, because T. minima requires high humidity for infection and development in order to cause significant disease, it would only be likely to establish in very limited areas of the State.  The pathogen is already established in several coastal areas, for the past several years, and rust disease appears typically only during early spring to summer following significantly wet periods.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 1

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Thekopsora minima has a moderate host range.  Main hosts of the pathogen are in the family Ericaceae and include blueberries, rhododendrons, and azaleas.

Evaluate the host range of the pest.

Score: 2

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Urediniospores are produced in abundance and ensure disease spread within the crop during the entire growing season. Spores are spread over short distances to nearby plants by wind and rain and may also be spread by human contact, clothing, equipment and packaging.  Long distance spread occurs mainly through passage of infected plants including fruit to non-infected regions.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: While blueberry rust disease has been reported to cause plant defoliation, this has not been the case in California, even though the fungus has been present in the State for several years. Blueberry growers have noted that some rust disease is apparent on blueberry leaves from early spring into summer following periods of significant rain, however, it is difficult to find infected plants later in the season.  Infected plants do not suffer from leaf drop, which is generally associated with the rust, and the pathogen has not been an issue of concern for blueberry growers to warrant administration of control measures.  No yield loss due to this rust pathogen in California has been observed or reported (see; ‘Damage Potential’).

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: None

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 1

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Although, horticultural and environmental plants, such as azaleas and rhododendrons, are hosts of Thekopsora minima (see: ‘Hosts’), the pathogen has not increased in its spread or impact in cultivated communities over the past several years of its presence in California.  Therefore, no significant impact on the environment or home/ornamental plantings is expected.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact:  None

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 1

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Thekopsora minima: Low (8)

Add up the total score and include it here.

–Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

6) Post Entry Distribution and Survey Information:  Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is Low.  Thekopsora minima has officially been detected only in few coastal counties in California.

Score: (-1)

-Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 7

Uncertainty:  

It is not known if the pathogen will infect hemlock (Tsuga spp.) in California, to complete its life cycle.  The pathogen was not recovered from hemlock in California and Oregon (Pacific coastal regions).  Hemlock species are widespread in California.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Thekopsora minima is C.

References:

Calflora.  2017.  Information on California plants for education, research and conservation. [web application]. 2017. Berkeley, California. The Calflora Database [a non-profit organization].  http://www.calflora.org/

EPPO.  2017.  Thekopsora minima (THEKMI).  EPPO Global Database (last updated: 2017-05-19).  https://gd.eppo.int/taxon/THEKMI/distribution.

French, A.M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento (Updated online version by T. Tidwell, May 2, 2017).

Mostert L., W. Bester, T. Jensen, S. Coertze, A. van Hoorn, J. Le Roux, E. Retief, A. Wood, and M C. Aime.  2010.  First report of leaf rust of blueberry caused by Thekopsora minima on Vaccinium corymbosum in the Western Cape, South Africa.  Plant Disease 95: 478.

Pfister, S. E., S. Halik, and D. R. Bergdahl.  2004.  Effect of temperature on Thekopsora minima urediniospores and uredinia.  Plant disease, 88: 359-362.

Rebollar-Alviter, A., A. M. Minnis, L. J. Dixon, L. A. Castlebury, M. R. Ramirez-Mendoza, H. V. Silva-Rojas, and G. Valdovinos-Ponce.  2011.  First report of leaf rust of blueberry caused by Thekopsora minima in Mexico. Plant Disease 95: 772.

Sato, S., K. Katsuya, and Y. Hiratsuka.  1993.  Morphology, taxonomy and nomenclature of Tsuga-Ericaceae rusts.  Transactions of the Mycological Society of Japan 34: 47-62.

Schilder, A. M. C., and T. D. Miles.  2011.  First report of blueberry leaf rust caused by Thekopsora minima on Vaccinium corymbosum in Michigan.  Plant Disease, 95: 768.  https://doi.org/10.1094/PDIS-12-10-0884.

Schrader, G., and W. Maier.  2015.  Express – PRA for Thekopsora minima occurrence. Julius Kühn-Institute, Institute for Plant Health.  Translated by Elke Vogt-Amdt.  http://pflanzengesundheit.jki.bund.de/dokumente/upload/fee0d_thekopsora-minima_express-pra.pdf

Shands, A. C., T. Ho, and T. D. Miles.  2017.  First report of leaf rust on southern highbush blueberry caused by Thekopsora minima in California.  Plant Disease (Accepted for publication).

Tasmania.  2014.  Blueberry rust (Thekopsora minima P. Syd & Syd).  Biosecurity Tasmania Fact Sheet, current as at October 2014. http://www.dpipwe.tas.gov.au/biosecurity/plant-biosecurity/pests-and-diseases.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved May 31, 2017. 6:30:49 pm CDT.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Wiseman, M. S., M. I. Gordon, M. L. Putnam.  2016.  First report of leaf rust caused by Thekopsora minima on Northern highbush blueberry in Oregon. Plant Disease 100: 1949.

Zheng, X., G. Tang, Y. Tian, X. Huang, X. Chang, H. Chen, H. Yang, S. Zhang, and G. Gong.  2017.  First report of leaf rust of blueberry caused by Thekopsora minima in China. Plant Disease 101: 835.  https://doi.org/10.1094/PDIS-09-16-1379-PDN

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

NOTE:

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Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Ramularia salviicola Tharp

California Pest Rating  for
Ramularia salviicola Tharp
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

On April 14, 2017, sage (Salvia sp.) plants showing symptoms of leaf spots were detected in a nursery in San Luis Obispo County by County Agricultural officials.  A sample of diseased leaves was sent to the CDFA Plant Pathology Laboratory for diagnosis.  On April 24, 2017, Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Ramularia salviicola associated with the diseased leaf tissue.  The pathogen was assigned a temporary Z rating as it has been recorded earlier in California, but never assigned a rating.  Subsequently, the consequences of introduction and establishment of R. salviicola in California are assessed and a permanent rating is proposed herein.

History & Status:

Background:   Ramularia salviicola is a fungal pathogen that causes leaf spot disease in host plants.  This pathogen was first discovered on Salvia farinacea in Austin Texas (Tharp, 1915).   Since then, it has only been reported from California on black sage, hummingbird sage and an unknown sage species (French, 1989).

Hosts:  Ramularia salviicola is only known to infect Salvia spp. (sage) in the family Lamiaceae: Salvia farinacea (mealycup sage), S. mellifera (black sage), Salvia sp. (sage), S. spathacea (hummingbird sage) (Braun, 1998; Farr & Rossman, 2017).

Symptoms:  Leaf spots are produced on both sides of living leaves.  Spots are subcircular to irregular, 1-10 mm in diameter, occasionally coalescing, brown with indefinite margin or with a diffuse yellowish halo, and sometimes divide into zones (Braun, 1998).

Disease development and spread: While there is a paucity of information reported on the specific biology of Ramularia salviicola, it is likely to be similar to that of other species within the genus.  Clusters of conidiophores arise from leaf lesions (spots) producing conidia (asexual spores) on living leaves.  Conidia are airborne and are spread accordingly to nearby plants.  It is also likely that, similar to other Ramularia species causing leaf spot disease, R. salviicola is transmitted as mycelium within the integument of seed and by movement of infested soil (Daughtrey et al., 1995),

Dispersal and spread: Infected plants and nursery stock, seeds, airborne conidia (Daughtrey et al., 1995).

Damage Potential: Quantitative losses due to Ramularia salviicola have not been reported.  Reduction in photosynthetic area due to leaf spotting can be expected as well as leaf wilt, premature leaf drop, and reduced tree vigor may result.  Leaf spot damage caused by R. salviicola may significantly impact commercial production and marketing of nursery ornamental plants, as well as private productions.  Black sage and hummingbird sage are perennial shrubs that are native to California and confined mainly to the southern and central coastal counties (Calflora, 2017).  Several other species of Salvia are also cultivated throughout California, but have not yet been reported as hosts of the pathogen.

Worldwide Distribution: North America: USA (California, Texas) (Braun, 1998; Farr & Rossman, 2017).

Official Control:  No official control for Ramularia salviicola has been reported.

California Distribution:  Southern coastal counties including, San Luis Obispo County.

California Interceptions:  None.

The risk Ramularia salviicola would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: In California, Ramularia salviicola has already become established in southern coastal regions where its hosts, black sage and hummingbird sage, are mainly cultivated. While the pathogen has not been reported from other regions it is likely to establish a larger but limited part of the State.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: The pathogen has only been found on Salvia

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Ramularia salviicola has high reproductive and dispersal potential. The pathogen is likely to be transmitted through movement of infected plants and nursery stock, integuments of seed and airborne conidia.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Ramularia salviicola causes leaf spot in sage plants.  While there is no information on quantitative crop loss caused by this pathogen, leaf spot disease could lower crop value and cause loss of markets.  Use of preventive chemical sprays and other control measures could increase production costs.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: B, C

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score:  2

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact:  The pathogen could significantly impact ornamental plantings in home/ urban, public gardens and other recreational environments.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Ramularia salviicola:  Medium (10)

Add up the total score and include it here.

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is High (-3).

Score: -1

-Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 7

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Ramularia salviicola is C.

References:

Braun, U. 1998. A Monograph of Cercosporella, Ramularia and Allied Genera (Phytopathogenic Hyphomycetes) Vol. 2.  IHW-Verlag 2: 439.

Calflora.  2017.  Information on California plants for education, research and conservation. [web application]. 2017. Berkeley, California. The Calflora Database [a non-profit organization].  http://www.calflora.org/

Daughtery, M. L., R. L. Wick, and J. L. Peterson.  1995.  Cyclamen stunt and Ramularia leaf spot of Cyclamen and Primula.  In Compendium of Flowering Potted Plant Diseases.  APS Press, The American Phytopathological Society.  Page 20.

Farr, D. F., and A. Y. Rossman.  2017.  Fungal Databases, U. S. National Fungus Collections, ARS, USDA. Retrieved June 5, 2017, from http://nt.ars-grin.gov/fungaldatabases/

French, A.M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento (Updated online version by T. Tidwell, May 2, 2017).

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

NOTE:

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Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Phytophthora cambivora (Petri) Buisman 1927

6 Comments
California Pest Rating for
Phytophthora cambivora (Petri) Buisman 1927
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

None.  The current risk and status of Phytophthora cambivora in California are reassessed and a permanent rating is proposed.

History & Status:

Background:  Phytophthora cambiv ora is an oomycete pathogen that can cause crown and root rot disease, usually in conjunction with other Phytophthora spp., in its hosts.  Phytophthora root and crown rot disease are among the most important soilborne diseases of stone fruits (Browne & Mircetich, 1995).  The pathogen is known to cause ink disease in chestnut.  It is widespread in temperate regions of all continents and occurs in soils of natural forests, agricultural fields, and orchards.  It can persist and spread in different environments and is capable of surviving in the soil as a saprophyte and by producing resting spores.

In California, P. cambivora has been found in several fruit and nut, forest, and native host plants, including: apple, avocado, American plum, apricot, chamise, hoary manzanita, palm, birchleaf mountain mahogany, apple avocado, American plum, apricot, sweet cherry, cherry plum, sour cherry, European plum, sweet almond, holly leaf cherry, Mahaleb cherry, peach, nectarine, Japanese plum, European/common pear, oak, canyon oak, California live oak, Japanese maple, toyon, madrone, bristlecone fir (French, 1989, CDFA Pest Damage Records).    Phytophthora diagnostic scientists have also found P. cambivora in other symptomatic (damaged) native plant species in natural stands in California.  These unpublished records of P. cambivora-infected native plants include, Ione manzanita (Arctostaphylos myrtifolia), sticky white leaf manzanita (A. viscida), pallid manzanita (A. pallida), Raiche’s manzanita (A. stanfordiana ssp. raichei), coyote ceanothus (Ceanothus ferriseae), valley oak (Quercus lobata), and California coffeeberry (Frangula californica) (comments from S. Frankel, plant pathologist, USDA Forest Service, and ‘Phytophthoras in Native Habitats Work Group’.  July, 2017).  The pathogen has also been recovered from various habitats including flowing water, stream and ditch banks, edges of roadsides and highways, forests, residential gardens, parks, cemeteries, recreational areas, and nurseries.

Saavedra et al., (2007) reported decline and mortality of golden chinquapin trees (Chrysolepis chrysophylla) in parts of northern and north-western California, similar to the damage caused by P. cambivora on the same host in Oregon.  The native range for this host species extends through the Coast Range Mountains from San Luis Obispo County, California, to Benton County, Oregon.

Recently, Jung et al., (2016) demonstrated by phylogenetic analysis that Phytophthora cambivora is a natural interspecific hybrid (a cross between two different Phytophthora species) in ITS Clade 7a, and, therefore, suggested that its name be changed to P. xcambivora.  Hybrid Phytophthora are often more aggressive than their parental species and fare better in nurseries and out-planted settings. Furthermore, P. xcambivora (= P cambivora) is the most thermo-tolerant of all species in Clade 7a, with the ability to grow at temperatures greater that 35°C.  This ability to grow at high temperatures enables the pathogen to grow in warm climates in California.

Hosts: Reported hosts of Phytophthora cambivora are present in 30 genera in 19 families: Abies bracteata (bristlecone fir), A. fraseri (fraser fir), A. procera (noble fir), Abies sp., Acer palmatum (Japanese maple), A. pennsylvanicum (striped maple), A. platanoides (Norway maple), A. rubrum (red maple), A. saccharum (sugar maple) , Acer sp., Adenostoma fasciculatum (chamise), Aesculus hippocastanum (horse chestnut), Alnus cordata (alder), A. rubra (red alder), Arbutus menziesii (madrone), Arctostaphylos canescens subsp. canescens (hoary manzanita), Areca sp. (palm),   Castanea sp. (chestnut), C. crenata (Japanese chestnut), C. dentata (American chestnut), C. mollissima (Chinese chestnut), C. pumila (allegheny chinquapin), C. sativa (chestnut), Castanea x coudercii (Couderc chestnut), Casuarina equisetifolia (casuarina), Cercocarpus betuloides (island mountain mahogany), C. montanus var. glaber (birchleaf mountain mahogany),  Chamaecyparis lawsoniana (Port Orford cedar), Chamaecyparis sp. (cypress/false cypress), Chrysanthemum cinerariifolium (pyrethrum), Chrysolepis chrysophylla (giant chinquapin), Cineraria sp., Dahlia campanulata (weeping tree dahlia), Erica sp., Eucalyptus sp. (eucalyptus), Fagus sp. (beech), F. sylvatica (common beech), Ficus carica (common fig), Heteromeles arbutifolia (toyon), Impatiens hawker (New Guinea impatiens), Juglans regia (English walnut), Juglans sp. (walnuts), Lithocarpus densiflorus (tanoak), Lobelia erinus (lobelia), Lupinus sp. (lupine), L. albus (white lupine), Malus sp. (ornamental species apple), M. domestica (apple), M. pumila var. domestica (apple), M. pumila var. dulcissima, M. sylvestris (European crab apple), Nothofagus sp. (southern beeches), Persea americana (avocado), Petunia parviflora (seaside petunia), Pieris sp., P. japonica (lily-of-the-valley shrub), Pisum sp., P. sativum (pea), Pistacia vera (pistachio), Poncirus trifoliata (hardy orange), Prunus sp., P. americana (American plum), P. amygdalus (almond), P. armeniaca (apricot), P. avium (sweet cherry), P. campanulata (Taiwan cherry), P. cerasifera (cherry plum), P. cerasus (sour cherry), P. domestica (European plum), P. dulcis (sweet almond), P. ilicifolia (hollyleaf cherry), P. mahaleb (Mahaleb cherry), P. persica (peach), P. persica var nectarina (nectarine), P. salicina (Japanese plum), Pyrus communis (European pear), P. serotina (black cherry), Quercus sp. (oak), Q. cerris (European Turkey oak) Q. agrifolia (California live oak), Q. alba (white oak), Q. chrysolepis (canyon oak), Q. macrocarpa (bur oak), Q. petraea (durmast oak), Q. ilex (holm oak), Q. robur (common oak), Q. rubra (northern red oak), Q. pubescens (downy oak), Rhododendron sp. (azalea), R. ponticum (common rhododendron), Rubus idaeus (American red raspberry), Senecio sp. (groundsel), S. cruentus, soil, Solanum tuberosum (potato), Tanacetum cinerariifolium (Pyrethrum), Taxus baccata (English yew), Ulmus sp. (elms), Vaccinium macrocarpon (cranberry), Vitis vinifera (grapevine)  (CABI, 2017; Farr & Rossman, 2017; French, 1989).

Symptoms: Phytophthora cambivora, along with other Phytophthora species, cause root and crown rot disease of walnut, cherry, apple, peach, plum, and apricot (CABI, 2017).  The expression of symptoms is dependent on the amount of root and crown tissue affected and speed of destruction.  Usually, crown rots advance rapidly and trees fall and die soon after the first warm weather of spring, while their leaves wilt, dry, and remain attached to the tree (Adaskaveg et al., 2009).  During early stages of infection, infected trees are difficult to differentiate from healthy, non-infected ones.  However, as the infection progresses, the leaves become small, chlorotic, and droopy, and grow slowly on terminal shoots.  A decline of infected trees sets in and sometimes trees without detectable symptoms die in early summer.  Collar and root rot may occur in the same tree.  Symptoms of P. cambivora often resemble those caused by other root rot or collar rot pathogens.  Collar rot is exhibited as decayed bark at the base of the trunk and can start at several points simultaneously, progressing until the lower part of the trunk is completely girdled.  Infected roots turn brown, brittle, and necrotic.  Infected root systems resulting in necrosis of lateral roots and taproots can affect top growth.  Vigorous trees with affected roots may not show appreciable crown symptoms (CABI, 2017).  Chronic infections, mainly of roots, cause reduction in growth, early senescence, and leaf fall, and may remain unthrifty for several years before succumbing to the disease.  Infected young trees are usually killed due to their small root systems and crown areas (Adaskaveg et al., 2015).

Disease development: Similar to most other Phytophthora spp., P. cambivora survives in the soil in the form of mycelium, sporangia, zoospores and oospores, and thrives in poorly-drained, water-saturated soils.  It lives as a saprophyte in litter and in soil containing dead organic material and is favored by moist and moderate climates in a wide range of pH: 3.8-7. It is not resistant to drought.  Optimum temperature range for growth is 22-24°C and maximum temperature (cessation of growth) is >32°C (CABI, 2017).  Jung et al., (2016), reported the ability for P. xcambivora (= P. cambivora) to grow at temperatures greater that 35°C.

Sporangia and zoospores of P. cambivora in humid soils are the main source of infection.  Sporangia are produced abundantly by young mycelia, which become sterile when they are more than 1 month old.  P. cambivora produces sporangia from 9 to 30°C.  Most sporangia are found on the ground surface in leaves, petals, or earthworm castings; within the upper 6 cm of soil, and near the crowns of trees (Cox, 2014).  Sporangia can germinate directly or, more commonly in P. cambivora, indirectly by producing zoospores at 9-27°C.  Zoospores allow a population to increase rapidly and disperse widely in films of free water.  Zoospores are expelled from sporangia under suitable temperature and moisture conditions and swim by means of their flagella towards their host in response to root exudates.  Once a zoospore comes in contact with a root, it germinates producing a germ tube, which penetrates the root directly under waterlogged soil conditions.   More mycelium develops, and eventually, oospores (sexual spores) are produced, and serve as resting structures that can survive for several years.  Phytophthora cambivora does not produce chlamydospores (thick-walled, asexual spores) (CABI, 2017).

Transmission: Like most Phytophthora species, P. cambivora is soil-borne and water-borne and may be spread to non-infected sites through infected plants, nursery and planting stock, and seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment, tools, and boots.  The pathogen is not seed-borne but can be spread by infected seedlings (CABI, 2017).  Irrigation water from canals, rivers, and ponds can be contaminated with Phytophthora spp. (Browne & Mircetich, 1995).

Damage Potential: Damage caused by Phytophthora cambivora alone may be difficult to assess as more than one species of Phytophthora may be associated with root and crown rot of host trees (Mircetich & Matherton, 1976).  Loss of production of apple, cherry, noble fir Christmas trees have been reported from North America (CABI, 2017).  Walnut, peach, plum and apricot are also susceptible to P. cambivora and other Phytophthora spp.  Nurseries, nursery stock and ornamental productions may be at risk and need to be monitored.

California’s native vegetation is also at risk of root and crown rot caused by P. cambivora and other Phytophthora spp., many of which are endemic (limited) to the State, while some are rare, endangered, or threatened plants, e.g., pallid manzanita, Ione manzanita, sticky white leaf manzanita, valley oak, bristlecone fir, coffeeberry, etc. (CNPS, 2017; Calflora, 2017).  Introduction of Phytophthora species are a threat to plant health in Bay Area restoration sites, where nursery stock is planted for flood control or to mitigate environmental impacts.   Detections on madrone, toyon, oaks, and manzanitas in native stands indicate that P. cambivora is capable of becoming established in a variety of native plant habitats under a range of soil and environmental conditions and can have negative impacts on native vegetation (comments from S. Frankel, plant pathologist, USDA Forest Service, and Phytophthoras in Native Habitats Work Group.  July, 2017).

Worldwide Distribution: Asia: India, Japan, Republic of Korea, Malaysia, Taiwan, Turkey; Africa: Madagascar, Mauritius, Nigeria, South Africa; North America: Canada, USA; Europe: Austria, Belgium, Croatia, Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, Netherlands, Norway, Poland, Portugal, Romania, Russian Federation, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom, Yugoslavia (former); Oceania: Australia, New Zealand, Papua New Guinea (CABI, 2017).

In the USA it has been reported from Alabama, Arizona, Arkansas, California, Georgia, Maryland, Michigan, Minnesota, Missouri, Montana, New Jersey, New York, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, Virginia, Washington, West Virginia (CABI, 2017).

Official Control:  Presently, Phytophthora cambivora is on the “Harmful Organism Lists” for Algeria, Canada, Chile, China, Honduras, Nicaragua, and Peru, while, Phytophthora spp. is on the “Harmful Organism Lists” for Peru and South Africa (USDA PCIT, 2017).

California Distribution: Phytophthora cambivora is widely distributed within California.  From 2013-April, 2017, the pathogen was officially detected in Alameda, Contra Costa, Marin, Monterey, Orange, Plumas, San Mateo, San Francisco, Santa Clara, Solano, and Sonoma Counties (CDFA Pest Damage Records).

California Interceptions:  None reported.

The risk Phytophthora cambivora would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Phytophthora cambivora has already established a large distribution under moist and cool to warm climates in California.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: The pathogen has a wide host range.

Evaluate the host range of the pest.

Score: 3

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Phytophthora cambivora, like other Phytophthora, has high reproductive capability under moist conditions.  It is dependent on moisture for spore dissemination and plant infection.  It is soilborne and may be spread to non-infected sites through infected plants, nursery and planting stock, and seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment, tools, boots, rivers, canals, and ponds.  Therefore, it is given a high rating in this category.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Damage caused by Phytophthora cambivora alone may be difficult to assess as more than one species of Phytophthora may be associated with root and crown rot of host tree.  Loss in production has been reported for apple, certain stone fruit, and noble fir Christmas.  Nursery productions of agricultural and environmental host planting stock, could be at risk. Controlling the disease include soil water management and use of resistant varieties, thereby requiring changes in cultural practices and increase in crop production costs.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, D, G

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: In conjunction with other Phytophthora, P. cambivora may be a contributor to root and crown disease of environmental plants. California’s native vegetation is at risk of root and crown rot damage caused by P. cambivora and other Phytophthora spp., many of which are endemic (limited) to the State, while some are rare, endangered, or threatened plants.  The pathogen is capable of becoming established in a variety of native plant habitats under a range of soil and environmental conditions and can have negative impacts on native vegetation.  Also, it may significantly impact ornamental planting.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: A, B, C, E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 3

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Phytophthora cambivora:

Add up the total score and include it here. 14

-Low = 5-8 points

-Medium = 9-12 points

–High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is Score: (-3)

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

 Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Phytophthora cambivora is B.

References:

Adaskaveg, J. E., J. L. Caprile, W. D. Gubler, B. L. Teviotdale.  2009.  Cherry: Phytophthora root and crown rot, pathogen: Phytophthora spp.  UCIPM Statewide Integrated Pest Management Program, University of California Agriculture & Natural Resources.  http://ipm.ucanr.edu/PMG/r105100711.html

Browne, G. T., and S. M. Mircetich.  1995.  Phytophthora root and crown rots.  In Compendium of Stone Fruit Diseases, Eds: J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu, and J. K. Uyemoto.  APS Press, The American Phytopathological Society. Pages 38-40.

CABI.  2017.  Phytophthora cambivora (root rot of forest trees) full datasheet.  Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/40956

Calflora.  2017.  Information on California plants for education, research and conservation. [Web application]. 2017. Berkeley, California. The Calflora Database [a non-profit organization].  http://www.calflora.org/

CNPS.  2017.  Inventory of rare and endangered plants of California (online edition, v8-03 0.38).  California Native Plant Society, Rare Plant Program. Website http://www.rareplants.cnps.org [accessed 10 August 2017].

Cox, K.  2014.  Phytophthora collar, crown, and root rots.  In Compendium of Apple and Pear Disease and Pests Second Edition Eds: T. B. Sutton, H. S. Aldwinckle, A. M. Agnello, J. F. Walgenbach.  Pages 63-65.

Farr, D. F., and A. Y. Rossman.  2017.  Fungal Databases, U.S. National Fungus Collections, ARS, USDA. Retrieved June 9, 2017, from https://nt.ars-grin.gov/fungaldatabases/

French, A.M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento (Updated online version by T. Tidwell, May 2, 2017).

Jung, T., M. H. Jung, B. Scanu, D. Seress, G. M. Kovács, C. Maia, A. Pérez-Aierra, T. –T. Chang, A. Chandelier, K. Heungens, K. van Poucke, P. Abad-Campos, M. Leon, S. O. Caciola, and J. Bakonyi.  2016.  Six new Phytophthora species from ITS Clade 7a including two sexually functional heterothallic hybrid species detected in natural ecosystems in Taiwan.  Persoonia 38: 100-135.

Mircetich, S. M., and M. E. Matherton.  1976.  Phytophthora root and crown rot of cherry trees.   Phytopathology 66: 549-558.

Saavedra, A., E. M. Hansen, and D. J. Goheen.  2007.  Phytophthora cambivora in Oregon and its pathogenicity to Chrysolepis chrysophylla.  Forest Pathology, 37: 409-419.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved June 6, 2017. 5:59:40 pm CDT.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

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 Pest Rating: B

Posted by ls