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Disease Control and Pest Management

Effect of Plant Residues on Chlamydospore Germination of Fusarium solani f. sp. phaseoli and on Fusarium Root Rot of Beans. J. A. Lewis, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; G. C. Papavizas, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 67:925-929. Accepted for publication 4 February 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-925.

The effects of decomposing immature and mature residues of rye, oat, soybean, sorghum, barley, buckwheat, timothy, and corn on Fusarium root rot of bean and on pathogen chlamydospore germination were determined. All mature (high C:N ratio) residues, but only two immature (low C:N ratio) residues, significantly reduced disease. Disease severity was positively correlated with total soil inorganic nitrogen and nitrate, but not with ammonium. Decomposing mature residues were more inhibitory than corresponding immature residues to chlamydospore germination in vitro and in soil, with rye being more effective than corn. Failure of the chlamydospores to germinate in vitro and in soil was related to nutrient deficiency in the soil as well as to formation of an inhibitory material from the decomposing residues. Fungistasis due to nutrient deficiency, but not toxicant production, was overcome in soil in the presence of nutrients.

Additional keywords: soil-borne pathogen, organic amendment, fungistasis.