Detection of the Nematophagous Fungus Hirsutella rhossiliensis in California Sugarbeet Fields

The nematophagous fungus, Hirsutella rhossiliensis, was detected in 10 of 21 sugarbeet fields in California. Fewer than four parasitized nematodes per 100 cm(3) soil were found in any field, and all parasitized specimens were the cyst nematode, Heterodera schachtii. Detection of the fungus was enhanced if soil samples were periodically inoculated with large numbers of healthy juveniles of H. schachtii prior to assay for the fungus. Detection efficiency was measured by assaying soil seeded with known numbers of parasitized H. schachtii. Detection was largely unaffected by soil type but declined from 63% at Time 0 to 17% after 2 days at 22 degrees C. Thus, the failure to detect H. rhossiliensis in 11 fields could reflect the absence of the fungus or limitations of the assay. The results suggest that a one-time release of H. rhossiliensis with the intention of establishing the fungus in sugarbeet fields is not a viable alternative for implementation of biological control of H. schachtii. (C) 1991 Academic Press, Inc.