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Physical Factors that Influence the Recovery of Microsclerotium Populations of Cylindrocladium crotalariae from Naturally Infested Soils. Gary J. Griffin, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; Don A. Roth(2), and Norris L. Powell(3). (2)(3)Department of Agronomy, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. Phytopathology 68:887-891. Accepted for publication 1 November 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-887.

Air-drying of soil (0.12 to 0.38% water or about 2,000 bars) resulted in no recovery of microsclerotia from soils, but rewetting soils to near field capacity for 1 to 4 wk before assay resulted in partial recovery from the deleterious effect of drying. Incubation of soil at low temperature (6 C) greatly reduced recovery of microsclerotia from soils. No microsclerotia were recovered from one soil incubated at 6 C for 1 mo. Incubation at 26 C had littler or no effect on microsclerotium recovery. Tests indicated that many small microsclerotia were present in Virginia peanut-field soils. The median 90% of microsclerotia recovered had a width in the range 25 to 103 μm; use of a sieve with a pore size of 25 μm or slightly smaller is recommended for recovery of microsclerotia. Little or no interference from conidium-or ascospore-size propagules in soil was found in assays using this sieve. Soil dispersion by blending or shaking was not essential for assaying sandy peanut-fields soils containing most microsclerotia free of organic matter.

Additional keywords: Cylindrocladium black rot, microsclerotium survival, peanut.