Correlations Between Most Probable Number and Activity of Nematode-Trapping Fungi

ABSTRACT Soil cages were used to determine whether nematode-trapping fungi population density, as measured by most probable number (MPN) procedures, was correlated with the trapping of nematodes. Fungi studied (and trap type) were Arthrobotrys oligospora (adhesive networks), A. eudermata (adhesive networks), A. dactyloides (constricting rings), Dactylellina ellipsospora (adhesive knobs), and D. haptotyla (adhesive knobs). The fungi were formulated as assimilative hyphae in dried alginate pellets. Pellets were added to field soil, the soil was packed into 80-cm(3) cages (PVC pipe, 3.0 cm long and 3.9 cm in diameter), and the cages were buried in vineyards. After 14 to 61 days, the cages were recovered, and MPN data and trapping activity were determined. For all five fungi, MPN data were correlated with the number of pellets added. Regardless of fungus population density, A. oligospora and A. eudermata trapped few if any nematodes in soil, and consequently, trapping and fungus population density were not correlated. The correlation between population density and trapping was weak for A. dactyloides but relatively strong for D. ellipsospora and D. haptotyla. High levels of trapping by the latter two fungi required more than 10(2) fungus propagules per gram of soil.