The Role of Organic Matter in the Population Dynamics of the Endoparasitic Nematophagous Fungus Drechmeria Coniospora in Microcosms

Abstract

Addition of organic matter to soil may indirectly enhance nematophagous fungi. The effect of organic amendments on the population dynamics of the endoparasitic nematophagous fungus Drechmeria coniospora was studied in soil microcosm experiments. In one experiment, soil was amended with lucerne meal, and in a second experiment the root system of barley served as the source of organic matter. Indigenous soil bacteria, the bacterivorous nematodes Rhabditis sp. or Acrobeloides butschlii, and D. coniospora were added as representatives of the first, second, and third trophic level. In lucerne meal amended soil, the conidial density of D. coniospora increased in response to increase in number of nematodes. Rhabditis sp. appeared to be a more susceptible host than A. butschlii. Nematode population density was suppressed by D. coniospora. In the rhizosphere of barley, a small but significant increase in the conidial density was measured as compared to the control without nematodes, but nematode numbers were not suppressed. In rhizosphere soil from two fields, the densities of endoparasitic and trapping fungi were not related to numbers of nematodes. Drechmeria coniospora was not detected in the field. We conclude that introduction of conidia of D. coniospora in combination with high input of organic matter may lead to suppressive levels of the fungus. The possible application for control of plant-parasitic nematodes is doubtful because of the narrow host range of the fungus.