Numerical responses of the nematophagous fungi Hirsutella rhossiliensis, Monacrosporium cionopagum, and M. ellipsosporum

Abstract

A soil microcosm experiment was conducted to measure the effect of nematode population density on suppression of nematodes by Hirsutella rhossiliensis, Monacrosporium cionopagum, and M. ellipsosporum. These fungi use adhesive conidia, branches, and knobs, respectively, to parasitize 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. Suppression was determined by adding a fixed number of the root-knot nematode Meloidogyne javanica and measuring the number (relative to a control without fungi) that penetrated the roots of a cabbage seedling planted in each microcosm. Suppression by M. ellipsosporum and H. rhossiliensis was positively related to S. glaseri density, suggesting that M. ellipsosporum, like H. rhossiliensis, depends on parasitism rather than on 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. Suppression by M. cionopagum increased rapidly to nearly 100% within 10 days following addition of fungal inoculum to soil and then declined sharply. Suppression by M. ellipsosporum increased gradually throughout the study and was nearly 100% at day 120. Suppression by H. rhossiliensis 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-parasitic nematodes.

Key Words:

• biological control
• density-dependent parasitism
• Hirsutella rhossiliensis
• Meloidogyne javanica
• Monacrosporium cionopagum
• M. ellipsosporum
• nematodes
• nematophagous fungi
• population regulation
• Steinernema glaseri