Variability among isolates of the nematophagous fungus Hirsutella rhossiliensis

Morphological, pathogenic and genetic variability among 25 isolates of the nematophagous fungus Hirsutella rhossiliensis was quantified and compared. Genetic variability was assessed with 36 RAPD markers that were generated with eight random decamer primers. Cluster analysis of the PCR products indicated substantial genetic variability among isolates of this species. Out of 300 possible isolate-isolate combinations, 193 had less than 50% similarity (shared polymorphisms). In contrast, most of the isolates were similar morphologically and pathogenically, regardless of host or geographical origin. We suggest that, in spite of substantial molecular divergence in isolated populations of this fungus, the environment selects for similar characteristics associated with pathogenicity. Isolates from nematodes in the Hoplolaimidae (Rotylenchus robustus and Hoplolaimus galeatus), however, grew slower on agar, produced larger conidia, and were less pathogenic towards nematodes than were isolates from other hosts.