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Rates of Spore Transmission, Mortality, and Production for the Nematophagous Fungus Hirsutella rhossiliensis. B. A. Jaffee, Associate professor, Department of Nematology, Universtiy of California, Davis 95616; A. E. Muldoon(2), R. Phillips(3), and M. Mangel(4). (2)Senior research associate, Department of Nematology, University of California, Davis 95616; (3)Graduate student, Graduate Group in Applied Mathematics, University of California, Davis 95616; (4)Professor, Department of Zoology and Center for Population Biology, University of California, Davis 95616. Phytopathology 80:1083-1088. Accepted for publication 30 April 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1083.

Transmission of spores of Hirsutella rhossiliensis to juveniles of Heterodera schachtii (J2) was quantified in soil microcosms (17 cm3) containing loamy sand (?60 mbar matric potential) or coarse sand (?20 mbar) at 20 C. Transmission, measured as the probability (P) of a J2 acquiring at least one spore (as a function of numbers of spores ? 103 per microcosm [S]), was greater in loamy sand (P = [1.05S]/[S + 31]) than in coarse sand (P = ?0.006 + 0.0016S). The value of P was constrained between 1 and 0. Differences in transmission were attributed to the effects of soil pore diameter on nematode motility and the probability of a nematode passing but not contacting a spore. The relative rate of spore mortality in microcosms (temperature and matric potentials as above) ranged from 0.072 to 0.103 per week. Some spores died shortly after sporulation and others were viable and virulent for at least 200 days. In moisture chambers at 20 C, H. rhossiliensis produced a mean of 112 spores per infected J2 after 12 days. Spore production per infected J2 was highly variable (range of 52 to 227).

Additional keywords: biological control, plant-parasitic nematode, soil porosity, sugar beet cyst nematode.