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Etiology

Soybean Seed Decay: Prevalence of Infection and Symptom Expression Caused by Phomopsis sp., Diaporthe phaseolorum var. sojae, and D. phaseolorum var. caulivora. K. T. Kmetz, Former Graduate Research Associate, Department of Plant Pathology, The Ohio State University, Columbus, OH 43210, Present address of senior author: E. I. du Pont de Nemours & Co., Wilmington, DE 19898; A. F. Schmitthenner(2), and C. W. Ellett(3). (2)(3)Professors, respectively, Ohio Agricultural Research and Development Center, Wooster, OH 44691. Phytopathology 68:836-840. Accepted for publication 5 December 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-836.

An undescribed Phomopsis sp., Diaporthe phaseolorum var. sojae (Dps) and D. phaseolorum var. caulivora (Dpc), the primary fungi associated with soybean seed decay, were isolated from immature, symptomless plants. Phomopsis sp. was detected more often than Dps at all stages of soybean growth, but Dpc was isolated infrequently and was first recovered shortly before plant maturity. Phomopsis sp. and Dps caused blotching and formed pycnidia on stems and pods of naturally or artificially infected mature plants. Appearance of blotching and pycnidia coincided with premature ripening on most plants in soil infected with Phomopsis. All three fungi were isolated infrequently from green seed but incidence increased as plants matured. Phomopsis was recovered significantly more often from immature and mature seed than was Dps, which was recovered more often than Dpc. All three were isolated from moldy and fissured seed. Percentage seed infected with Phomopsis and Diaporthe increased and germination decreased with harvest delay. Seed inoculated with Phomopsis, Dps, or Dpc or from highly-infected seed lots germinated poorly in nonsterile soil.