VIEW ARTICLE

Ecology and Epidemiology

Effect of Pod Development Stage, Temperature, and Pod Wetness Duration on the Incidence of Purple Seed Stain of Soybeans. Wolfgang Schuh, Assistant professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; Phytopathology 82:446-451. Accepted for publication 21 October 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-446.

The incidence of soybean seed infected by Cercospora kikuchii was influenced by temperature, length of pod wetness period, and developmental stage of the soybean pods at the time of inoculation. The statistical significance was determined using logistic regression. Infected seeds were observed when small pods (<0.5 cm in length) and large pods (0.5–2.0 cm in length) were inoculated with a conidial suspension. No infection was observed when flowers in full bloom or postbloom (desiccated petals) stages were inoculated. The optimal temperature for infection was 25 C; no infection was observed at 15 and 35 C. In general, disease incidence increased with increasing pod wetness periods of up to 30 h. In some temperature/pod wetness combinations, disease incidence decreased when the pod wetness was further increased to 36 h. No disease was observed at pod wetness periods of less than 24 h. To describe effects of environment on purple stain incidence in pods, logistic regression models were developed separately for each pod developmental stage. The models contained linear and quadratic and interaction terms for both temperature and leaf wetness duration and satisfactorily described the data. Seed infection and seed germination were not significantly related.