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Inoculum Pattern, Inoculum Density-Disease Incidence Relationships, and Population Fluctuations of Cylindrocladium crotalariae Microsclerotia in Peanut Field Soil. John D. Taylor, Research associate, Virginia Polytechnic Institute and State University, Blacksburg 24061; Gary J. Griffin(2), and Kenneth H. Garren(3). (2)Professor of Plant Pathology, Virginia Polytechnic Institute and State University, Blacksburg 24061; (3)Plant pathologist, AR, SEA, USDA, Tidewater Research and Continuing Education Center, Suffolk, VA 23437. Phytopathology 71:1297-1302. Accepted for publication 13 April 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1981. DOI: 10.1094/Phyto-71-1297.

The horizontal pattern (distribution) of Cylindrocladium crotalariae microsclerotial inoculum in soil was determined in a 1975 field plot established to study inoculum density-disease relationships and the influence of crop rotation on pathogen populations. The microsclerotial-inoculum pattern fitted the negative binomial distribution, indicating the microsclerotial-inoculum pattern was not random but was clumped or clustered. From 1975 to 1977, appreciable incidence of Cylindrocladium black rot of peanut was found only in 1976 (mean = 18.0%). For that year, first-order regression equations gave the best fit in arithmetic plots of inoculum density vs disease incidence (transformed to loge [1/1y]). Log 10-log10 regression line slopes of the same variables were low for both a corn-peanut sequence (b = 0.45) and a peanut-peanut sequence (b = 0.30). Inoculum clumping appeared to contribute to the low slope values. Physical environmental factors had a greater influence on the quantity of microsclerotia in soil than did crop sequence. A drought period in June 1975 was associated with a reduction in microsclerotial populations in the upper (0 to 12.7 cm) soil layer, compared to populations in the 12.7- to 25.4-cm soil layer. The extremely cold winter of 19761977 was associated with a large decrease in germinable microsclerotia in all field-plot soils between 1976 and 1977. Microsclerotial populations remained low following a cold winter in 1977-1978.

Additional keywords: inoculum potential.