Distribution of Hypocotyl Rot Caused in Snapbean byRhizoctonia solani

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Abstract
Hypocotyl rot caused by R. solani in snapbean (P. vulgaris) is a potentially destructive disease wherever snapbeans are grown. To investigate this disease system quantitatively, 6 snapbean fields in central Pennsylvania [USA] were selected and a 0.4 ha section of each field was divided into 100 contiguous 6 .times. 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.

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