Nematode-trapping fungi constitute a guild of species that develop specialized trapping structures with which they capture and digest nematodes. These traps are not con-stitutively present, but instead develop in the presence of nematodes3; they attract them2, adhere to their cuti-cle and eventually pierce it, extending hyphae inside their bodies.

Due to the fact that many nematode species behave as pests and diseases, groups of fungi with nematode-antagonistic effects are interesting due to their potential uses in biocontrol^1,4. Here we describe the progression of the nematode-trapping process by Arthrobotrys oligospora Fres. (Helotiales: Orbiliaceae) (isolate INTA10, obtained from soil of an organic tomato farm in La Plata area, Argentina [S 35°06' W 58°12']) on the free-living nematode Panagrellus redivivus Linn. (Rhabditidae: Panagrolaimidae).

INTA10 was grown on 90 x 15 mm oatmeal agar culture plates in the dark at 24 ±1 °C until the plate was covered (72 h). Twelve plates were prepared. Approximately 5000 nematodes were inoculated on each plate, and dispersed freely across the culture. Every 6h after nematode inoc-ulation (t = 6, 12, 18, and 24) three cultures were stained using methylene blue (0.1% w/v) and immediately rinsed with sterile physiological solution, while the remainder of the cultures was allowed to continue its development. Stained cultures were examined using a compound micro-scope (Leica, DM E) to observe trapping progression (Fig. 1). Developed traps (indicated with arrows, Fig. 1A) with alive, recently caught nematodes were found at t = 6. Fungal col-onization inside the nematodes was detected at t = 24, with the presence of blue-dyed hyphae growing inside them (indicated with arrows in Fig. 1B, shown magnified in Fig. 1C).

Figure 1: Progression of nematicidal activity of Arthrobotrys oligospora INTA10 on Panagrellus redivivus. Nematode trapped by adhesive fungal structures (t = 6) (A) (200x). Hyphal growth inside partially decayed nematodes (t = 24) (200x) (B) and (300x) (C). Detail of traps (400x) (D). 

Figure 1D shows the multicellular, tridimensional adhesive traps stemming from the mycelium in further detail.

Acknowledgments

DS holds a research career award from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET).