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Ecology and Epidemiology

Sporulation of the Nematophagous Fungus Hirsutella rhossiliensis from Hyphae Produced In Vitro and Added to Soil. B. A. Lackey, 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 82:1326-1330. Accepted for publication 14 August 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-1326.

After assimilating and killing host nematodes, Hirsutella rhossiliensis sporulates (i.e., produces external hyphae, phialides, and spores) from assimilative hyphae within the cadaver; the spores adhere to and infect nematodes. The ability of the fungus to sporulate from hyphae produced in vitro, rather than in host nematodes, was tested. Hyphae in the form of discrete vegetative colonies were grown in shake culture (potato-dextrose broth). In moist chambers, sporulation from vegetative colonies (rinsed free of broth) and from host nematodes was identical. To determine whether vegetative colonies sporulated in soil, vials were packed with nonheated, heated, or autoclaved loamy sand (17 cm3) containing 050 rinsed vegetative colonies. After 14 days at 20 C, healthy juveniles (J2) of Heterodera schachtii were added and recovered 66 h later. The percentage of J2 with at least one attached spore of H. rhossiliensis increased nonlinearly with increased numbers of colonies added per vial. The percentage was not affected by soil treatment, and virtually all J2 with attached spores were infected by the fungus. Approximately four vegetative colonies per 17 cm3 of soil were required to obtain 50% parasitism of J2 in loamy sand and in six other raw soils that varied in texture and other properties. Penetration of cabbage roots by J2 was suppressed in raw loamy sand containing rinsed vegetative colonies. Vegetative colonies did not affect growth of seven plant species in the absence of nematodes. Results suggest that hyphae of H. rhossiliensis produced in vitro and added to soil without organic substrate may be used for biological control of plant-parasitic nematodes.

Additional keywords: beet cyst nematode, formulation, hyperparasitism, inundative release.