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Ecology and Epidemiology

Activity of Fungistatic Compounds from Soil. J. A. Liebman, Department of Plant Pathology, University of California, Berkeley 94720; L. Epstein, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 82:147-153. Accepted for publication 13 August 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-147.

Propagules of many fungi do not germinate in soil unless provided with nutrients. According to the nutrient deprivation hypothesis, soil microflora prevent germination by acting as a sink for nutrients that leak from fungal propagules. Alternatively, soil microflora may produce germination inhibitors. In this study, fungistatic activity diffused from soil into agarose blocks and was quantified by percentage of germination of Cochliobolus victoriae conidia incubated on the blocks. The blocks were kept sterile and separate from soil by placement either on polycarbonate membranes with 0.2-m pores (diffusion assay) or on glass (volatile assay). Conidia on membranes also were exposed to soil without agarose (direct assay). Four test soils were fungistatic and gave similar results in all assays. Agarose blocks became more fungistatic with increasing time on soil. Thin (2.5 mm) blocks became fungistatic more quickly than thick (7.5 mm) blocks, and blocks became fungistatic more quickly in the diffusion assay than in the volatile assay. Activity persisted in the blocks after removal from soil, and persisted longer when blocks were incubated in still rather than moving air. The results of this study do not support the nutrient deprivation hypothesis. Furthermore, the results indicate the occurrence of water-soluble, volatile, and possibly nonvolatile, fungistatic compound(s) in a variety of soils.

Additional keywords: Bipolaris, Helminthosporium, mycostasis.