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Effect of Soil Moisture and Texture on Transmission of the Nematophagous Fungus Hirsutella rhossiliensis to Cyst and Root-Knot Nematodes. E. C. Tedford, Department of Nematology, University of California, Davis 95616-8668; B. A. Jaffee, and A. E. Muldoon. Department of Nematology, University of California, Davis 95616-8668. Phytopathology 82:1002-1007. Accepted for publication 15 June 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-1002.

The nonmotile spores of Hirsutella rhossiliensis adhere to and initiate infection of vermiform nematodes in soil. Transmission of spores to second-stage juveniles (J2) of Heterodera schachtii and Meloidogyne javanica was quantified in vials that contained 15–17 cm3 of loam, loamy sand, or sand in the absence of a host plant. Fungal inoculum was added to the soil at day 0 as colonized nematodes from which the fungus sporulated, and healthy J2 of H. schachtii or M. javanica were added after 14 days at 20 C and were extracted 66 h later. Transmission (measured as the probability [P] of a J2 acquiring at least one spore) to both nematodes and in all three soils was inversely related to soil matric potential between –80 and near 0 J kg–1. Reduced transmission at high water potentials appeared to reflect reduced sporulation of the fungus rather than reduced movement of nematodes. Transmission to H. schachtii was greater or equal to transmission to M. javanica. Transmission to both nematodes was greatest in loamy sand, intermediate in loam, and lowest in sand. The equation P = 1 – e–tr*col (where col = number of colonized nematodes added per vial at day 0 and tr = transmission parameter) described transmission to M. javanica. This equation, which previously was found to describe transmission of H. rhossiliensis to H. schachtii, enabled comparisons among experiments and will facilitate the incorporation of transmission data into epidemiological models.

Additional keywords: biological control, endoparasitic, epidemiology, modeling, parameter estimation, soil water.