Intraspecific variability in nematicidal response of Arthrobotrys oligospora, a natural enemy of plant-parasitic nematodes, and how it is affected by availability of prey.

The nematophagous fungus Arthrobotrys oligospora (Leotiomycetes: Heliotales) has for a long time incited interest inits potential as a biological control agent of plant-parasitic nematodes in agriculture. However, efforts to materialise these aspirations have been hindered by inconsistent results. Many research papers on the subject deal with one particular strain of A. oligospora, but their conclusions are often assumed to be valid for the whole species. We hypothesize that one of the causes for the inconsistences is that the natural variation in the nematicidal response between different strains of A. oligospora, as well as how prey availability in the experimental design can affect results, is often overlooked. In this work, we evaluate the in vitro nematicidal response of 11 strains of A. oligospora over the first 12 hours of contact with the model nematode Panagrellus redivivus. Strain INTA10 had significantly higher and faster nematicidal activity than the rest (LT50 after 247 minutes, Mean=0.55 n=6 SD=0.24 Tukey post-hoc: F=13.20, p<0.0001; LT100 after 719 minutes, Mean=1 n=6 SD=0 Tukey post-hoc: F=18.29, p<0.0001). Additionally, we studied how in vitro nematicidal activity is affected by the availability of prey, using strain INTA10 with four prey densities, 75, 25, 10, and 3 P. redivivus/cm², over the first 11 hours of contact. Although mortality over time curves followed a similar pattern across treatments, we found significant differences between them, with intermediate prey densities eliciting a faster response, and higher final mortalities. Our results stress the importance of evaluating A. oligospora as individual strains, show how different experimental designs can affect results, and highlight the risks of assuming that results obtained in one strain in certain particular conditions apply to the whole species.