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Ecology and Epidemiology

Suppression of Conidial Germination of Helminthosporium victoriae in Soil and in Model Fungistatic Systems. Lynn Epstein, Graduate research assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312; J. L. Lockwood, professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312. Phytopathology 74:90-94. Accepted for publication 22 June 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-90.

Conidia of Helminthosporium victoriae germinated most rapidly in a sterile salts solution at 30 C, ~pH 5, and osmotic potential from - 0.2 to - 1.2 bar. Of several buffers tested, 2-(N-morpholino)ethanesulfonic acid (MES) was the most suitable for germination. In a sterile sandy clay loam soil, germination was most rapid at a matric potential of 0 bar. Germination of conidia incubated at 20 C on sterile sand while being leached with 10% White' s salts solution was inversely correlated with flow rate. In contrast, ~85% of the conidia germinated on sand leached at all flow rates with 0.01 M MES (pH 5.0) in 10% White' s solution at 30 C. The amount of exudation from 14C-labeled conidia leached for 30 min was positively correlated with flow rate in either a germination-suppressive or germination-conducive environment. Thus, the suppression of germination in soil or in the leaching system cannot be attributed solely to the loss of exudate. The environmental conditions (pH, temperature, and water potential) that allowed germination in the leaching apparatus were largely ineffective in promoting germination in nonsterile soil.