Relationships between the spatial pattern and number of apothecia of Sclerotinia sclerotiorum and stem rot of soybean

Abstract

Relationships between the spatial patterns and numbers of apothecia of Sclerotinia sclerotiorum and incidence of sclerotinia stem rot of soybean (Glycine max) were investigated in a field plot in 1981 and 1982. Apothecia and disease were both spatially aggregated and were most consistently described by the negative binomial distribution, although the Poisson‐binomial and logarithmic with zeros distributions sometimes gave significant fits to data. Numbers of apothecia and disease incidence were correlated within quadrats of 1.4 m 2 (r = 0.04‐0.57), 36 m 2 (r = 0.44‐0.87) and 108 m 2 (r = 0.44‐0.99). The results suggest that disease incidence was determined primarily by inoculum produced within the field. This information may be important in developing models for disease production.