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Ecology and Epidemiology

Distribution of Hypocotyl Rot Caused in Snapbean by Rhizoctonia solani. C. Lee Campbell, Former graduate fellow, Department of Plant Pathology, The Pennsylvania State University, University Park, 16802, Present address of senior author: Department of Plant Pathology, North Carolina State University, Raleigh 27650; S. P. Pennypacker, associate professor, Department of Plant Pathology, The Pennsylvania State University, University Park, 16802. Phytopathology 70:521-525. Accepted for publication 25 September 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-521.

Hypocotyl rot caused by Rhizoctonia solani in snapbean (Phaseolus vulgaris) is a potentially destructive disease wherever snapbeans are grown. In order to investigate this disease system quantitatively, six snapbean fields in central Pennsylvania were selected and a 0.4-ha section of each field was divided into 100 contiguous 6 × 6 m quadrats. Plants were removed from each quadrat and hypocotyls were evaluated to determine the number of infected plants per quadrat and number of lesions induced by R. solani per quadrat. The presence of R. solani in lesions was verified by standard isolation and identification techniques. Variance-to-mean ratios of infected plants per quadrat were not significantly greater than unity for all samples and data for each sample were adequately fit by the Poisson distribution function which indicated a random dispersion of infected plants. Fungal lesions were clustered as indicated by variance-to-mean ratios greater than unity for all samples and the goodness of fit of all data sets by the negative binomial distribution function.