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Ecology and Epidemiology

Decreased Virulence of Cochliobolus victoriae Conidia After Incubation on Soils or on Leached Sand. A. B. Filonow, Former research associate, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312, Present address: Department of Plant Pathology, Oklahoma State University, Stillwater 74078; C. O. Akueshi(2), and J. L. Lockwood(3). (2)(3)Former research associate and professor, respectively, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312, (2)Present address: Department of Botany, University of Jos, P.M.B. 2084, Jos, Nigeria. Phytopathology 73:1632-1636. Accepted for publication 22 June 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/Phyto-73-1632.

Conidia of Cochliobolus victoriae on membrane filters were aseptically incubated for 15- 30 days on leached sand or on five soils. Virulence of conidia was assessed using susceptible, aseptic oat seedlings in glass vials inoculated with 10- 10⁴ incubated or nonincubated conidia per vial. Seedlings in vials inoculated with incubated conidia usually had significantly (P = 0.05) reduced disease indices and longer roots and coleoptiles than seedlings inoculated with nonincubated conidia. Similar results were obtained with seedlings in soils. Incubated conidia also showed an increased dependence on exogenous nutrients for germination, retarded rates of germination, and reduced viability. Incubated conidia at inoculum densities two or more times those of nonincubated conidia produced less disease than nonincubated conidia, suggesting that decreased viability after incubation was not solely responsible for decreased virulence. The results indicate that prolonged exposure to soils can reduce the virulence of conidia of C. victoriae.