Influence of Prebloom Disease Establishment by Botrytis cinerea and Environmental and Host Factors on Gray Mold Pod Rot of Snap Bean. K. B. Johnson, Graduate Research Assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. M. L. Powelson, Assistant Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Plant Dis. 67:1198-1202. Accepted for publication 29 April 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1198.

Observations on the development of gray mold of snap beans in five commercial fields in the Willamette Valley of Oregon revealed that Botrytis cinerea colonized senescing cotyledons first. Young stem and leaf tissues also became diseased before bloom and served as within-field inoculum sources. Infected stems were the most durable prebloom inoculum source and continuously produced inoculum into the bloom period. The average number of sporulating prebloom infections varied among fields, ranging from 0.2 to 14.8 per 5-m row. Both the number of spores per plant at bloom initiation and the incidence of B. cinerea on blossoms at full bloom were positively correlated with the number of sporulating prebloom infections. When the number of sporulating infections before bloom was used as a predictive variable, 50% of the variation in the incidence of pod rot among fields could be explained. A multiple regression model that included the number of sporulating infections before bloom, interval between irrigations, cumulative duration of leaf wetness due to irrigation and rain, and canopy size explained 82% of the variation in percent pod rot among fields.

Keyword(s): disease forecasting, epidemiology.