NUMERICAL RESPONSES OF THE NEMATOPHAGOUS FUNGI HIRSUTELLA-RHOSSILIENSIS, MONACROSPORIUM-CIONOPAGUM, AND MONACROSPORIUM-ELLIPSOSPORUM

A soil microcosm experiment was conducted to measure the effect of nem atode population density on suppression of nematodes by Hirsutella rho ssiliensis, Monacrosporium cionopagum, and M. ellipsosporum. These fun gi use adhesive conidia, branches, and knobs, respectively, to parasit ize nematodes, and were added to soil in the form of pelletized hyphae . Nematode population density was controlled by adding small to large numbers of the insect-parasitic nematode Steinernema glaseri. Suppress ion was determined by adding a fixed number of the root-knot nematode Meloidogyne javanica and measuring the number (relative to a control w ithout fungi) that penetrated the roots of a cabbage seedling planted in each microcosm. Suppression by M. ellipsosporum and H. rhossiliensi s was positively related to S. glaseri density, suggesting that M. ell ipsosporum, like H. rhossiliensis, depends on parasitism rather than o n saprophytism. The response of M. cionopagum to nematode density was inconsistent. In a second experiment, the change in suppression of M. javanica over time was measured in soil containing few nematodes. Supp ression by M. cionopagum increased rapidly to nearly 100% within 10 da ys following addition of fungal inoculum to soil and then declined sha rply. Suppression by M. ellipsosporum increased gradually throughout t he study and was nearly 100% at day 120. Suppression by H. rhossiliens is increased to only about 50% by day 20 and then declined gradually. Overall, the two trapping fungi appear to have greater potential than does H. rhossiliensis for biological control of certain plant-parasiti c nematodes.