NEMATODE-TRAPPING FUNGI OF A NATURAL SHRUBLAND - TESTS FOR FOOD-CHAININVOLVEMENT

We describe the spatial and temporal patterns in the abundance of nema tode-trapping fungi and in suppression of nematodes in a coastal shrub land. A previous study at this location (Bodega Marine Reserve, Sonoma County, California) had documented a soil food chain in which an inse ct-parasitic nematode consumes and kills the soil-dwelling larva of th e ghost moth, which otherwise consumes and kills the bush lupine; the patchy distribution of the nematode and lupine suggest the involvement of nematophagous organisms, including nematode-trapping fungi. To tes t our model (trapping fungi kill insect-parasitic nematodes, and there fore ghost moths persist and kill lupines at some sites), we hypothesi zed that sites with substantial lupine mortality would contain larger numbers of nematode-trapping fungi and would be more suppressive to ne matodes than would sites with little lupine mortality. Soil was collec ted from eight sites (four with substantial lupine mortality and four with little lupine mortality) at 2-mo intervals for I yr and subjected to dilution plating and most probable number procedures. Nematode-tra pping fungi detected were Arthrobotrys brochopaga, A. musiformis, A. o ligospora, A. superba, Geniculifera paucispora, Hirsutella rhossiliens is, Monacrosporium cionopagum, M. doedycoides, M. eudermatum, M. parvi collis, Nematoctonus concurrens, and Stylopage sp. A. oligospora was t he most abundant. Some soil samples contained large numbers of nematod e-trapping fungi (as many as 695 propagules/g of soil), but sites with substantial lupine mortality did not contain larger numbers than did sites with little mortality. In a laboratory bioassay, suppression of the root-knot nematode Meloidogyne javanica was significant in 44% of the samples, but suppression was not correlated with fungal population density; moreover, soil from sites with substantial lupine mortality was less suppressive than was soil from sites with little mortality. T he spatial and temporal patterns in fungal abundance and in nematode s uppression, therefore, did not support our model that nematode-trappin g fungi cause the patchy distribution of the insect-parasitic nematode and hence of lupine. Nevertheless, we must be conservative in rejecti ng the involvement of these fungi in the food chain, because methods f or fungal quantification have important limitations.