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Myrothecium leaf spot of cotton
- 1. Presented by Miss. SRUTHI A B B.Sc Agriculture
- 2. Name of the disease Myrothecium leaf spot ©http://:cotton.ces.ncsu.edu
- 3. Occurrence:© Brazil, Ecuador, Columbia, India, Pakistan, China. History: Myrothecium leaf spot was first observed on the fields in Maranhao State, Brazil, causing yield reduction upto 60%.
- 4. Symptoms: o Initially, reddish spots of 0.5mm to 1cm diameter may appear on the margin of the leaves. o Disease symptoms are lesions with concentric necrotic rings, with salient structures(sporodochia) irregularly distributed. o The affected portions fall off leaving irregular shot holes on the leaves. o The symptoms are observed on the petioles, bracts, leaves and bolls.
- 6. Isolation: o The pathogen was isolated and extracted in Potato- dextrose-agar medium. o Thirteen isolates of M. roridum were tested, which includes 8 from cotton and 5 from soyabean. o Fungal structures were evaluated by using light microscope with ocular micrometer. o The MA-75 was the most aggressive strain. o Spores from cotton isolates are 5,1µm × 1,5µm. o This is the first report on Myrothecium leaf spot from Brazilian cotton fields.
- 7. Pathogen: o Myrothecium roridum Tode ex Fr. o Conidia are hyalines due to dilute olivaceous, single- celled, abundantly produced in a dark green to black aggregate mass. o Spores from cotton isolates are 5,1µm × 1,5µm.
- 8. Systematic position: Kingdom: Fungi Division: Ascomycota Class: Sordariomycetes Order: Hypocreales Family: incertae sedis Genus: Myrothecium Species: M. roridum
- 9. Spread: Spread by the presence of conidia present in the infected fallen leaves.
- 10. Favourable condition: o In vitro studies show that the maximum disease development was reported at 25ºC±1 in both Bt cotton and non Bt cotton crops. o Average humidity: 84.7%. o Rain: 11.4mm. o pH : 6. o Heavy during June – October. o Dense crop canopy. o The leaf spot incidence increased with delay in sowing date at 15 days interval from 1-April to 1- june.
- 11. Disease management: Resistant varieties: No varieties released yet. Cultural management: Remove and destroy infected plant parts.
- 12. Biological management: By medicinal plant extract: Maximum inhibition ia obtained at 5% solvent extract of Datura metal followed by Alium sativum and Eucalyptus citriodora. By bioagent: Apply Trichoderma harzianum, Pseudomonas fluorescens.
- 13. Chemical management: o Spray Mancozeb or Copper oxychloride at 2kg/ha at the intimation of the disease. o Two to three sprays may be given at 15 days interval. o In vitro studies indicated that propiconazole and cobalt chloride at 100 and 1000 ppm conc gave 100 and 87.9% growth inhibotion of M. roridum. o Foliar spray of propiconazole and salicylic acid at 0.1% and 0.01 % effectively controls disease.