Simple Screening Methods for Assessing the Predacious Activity of Nematode-Trapping Fungi

Australian isolates of nematode-trapping fungi were screened for activity against nematodes on agar and in soil. All isolates produced traps extensively on agar in response to Caenorhabditis elegans and, within 1-3 days, populations of this nematode were generally reduced by at least 90%. Juveniles of Meloidogyne javanica induced fewer traps on agar and most fungi took more than 3 days to reduce numbers of nematodes by more than 90%. Experiments in microcosms showed that predacious activity on agar gave little indication of the capacity of a fungus to trap nematodes when added to mineral soil. Species such as Dactylella candida and Arthrobotrys dactyloides, which formed detachable rings and knobs or constricting rings, consistently reduced the number of M. javanica juveniles recovered from soil whereas network-forming species sometimes did not. In studies using agar 'sandwich' and buried slide techniques to monitor trapping activity in soil, D. candida and A. dactyloides consistently produced traps within 5 days of being introduced, whereas network-forming species produced few traps in soil and their trapping activity varied from experiment to experiment.