VIEW ARTICLE

Ecology and Epidemiology

Relationship Between Weather and Soybean Seed Infection by Phomopsis sp.. D. M. TeKrony, Professor, Department of Agronomy, University of Kentucky, Lexington 40546-0091; D. B. Egli(2), R. E. Stuckey(3), and J. Balles(4). (2)Professor, Department of Agronomy, University of Kentucky, Lexington 40546-0091; (3)Associate extension professor, Department of Plant Pathology, University of Kentucky, Lexington 40546-0091; (4)Former graduate research assistant, Department of Agronomy, University of Kentucky, Lexington 40546-0091. Phytopathology 73:914-918. Accepted for publication 19 January 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-914.

Five soybean (Glycine max) cultivars were planted at three dates in the field for 4 yr to investigate the relationship between seed infection by Phomopsis sp. and environmental conditions. Weather data were summarized during two growth periods: seed development (from the beginning of seed filling to physiological maturity) and seed maturation (physiological maturity to harvest maturity). Seed infection by Phomopsis sp. ranged from zero to 68% across years, cultivars, and planting dates. The incidence of Phomopsis sp. was significantly correlated with air temperature and minimum relative humidity but not with total precipitation or precipitation per day. A regression model was developed that included minimum temperature and minimum relative humidity during both growth periods, precipitation per day during the seed development period, and interactions between growth periods (nine terms, r² = 0.70). It accurately predicted Phomopsis sp. infection when tested with data independent of those used to develop the model. The model predicted low levels (3%) of Phomopsis sp. seed infection from long-term average weather data for Lexington, KY, for an early maturing cultivar planted early (mid-May). Predicted levels increased to 39% when all weather variables were increased to 20% above average. Similar increases occurred when only the moisture variables were increased to 20% above average, but little increase occurred if temperature alone was increased by 20%, suggesting that infection of soybean seed by Phomopsis sp. depends more on moisture than on temperature at Lexington, KY.