CONIDIAL TRAP FORMATION OF NEMATODE-TRAPPING FUNGI IN SOIL AND SOIL EXTRACTS

Conidial traps (CT) in nematode-trapping fungi are trapping structures formed directly on germination of conidia, without an intermediate hy phal phase. Most of the nine fungi tested were able to form CT on wate r agar surfaces in the vicinity of soil, but the ability varied betwee n species. Generally, the ability to form CT was greatest in Arthrobot rys dactyloides and Monacrosporium gephyropagum followed by Arthrobotr ys superba and Arthrobotrys oligospora. The mechanism behind CT format ion was further studied in soil extracts using a microwell plate assay . Preincubation of soil or soil extracts at room temperature before in oculation with conidia increased the incidence of CT. Reduction of the number of microorganisms in soil extracts by sterile filtration, dilu tion or heating decreased CT formation, as did the addition of nutrien ts. The results suggest that a certain level of competition for nutrie nts by microorganisms is necessary for CT formation. In contrast, we w ere unable to induce CT when conidia were allowed to germinate in pure culture on hyphal trap-inducing or non-inducing agar media with or wi thout cell wall affecting compounds.