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Ecology and Epidemiology

Evaluation of Seedborne Xanthomonas phaseoli and X. phaseoli var. fuscans as Primary Inocula in Bean Blights. David M. Weller, Former graduate student, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, Present address of senior author: Regional Cereal Disease Laboratory, Science and Education Administration, Agricultural Research, U.S. Department of Agriculture, Washington State University, Pullman 99164; A. W. Saettler, research plant pathologist of edible legumes, Science and Education Administration, Agricultural Research, U.S. Department of Agriculture, Michigan State University, East Lansing 48824. Phytopathology 70:148-152. Accepted for publication 16 August 1979. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1980. DOI: 10.1094/Phyto-70-148.

The roles of several types of seedborne Xanthomonas phaseoli (Xp) and X. phaseoli var. fuscans (Xpf) were evaluated in the epidemiology of common (caused by Xp) and fuscous (caused by Xpf) bacterial blights of navy beans. Seeds externally infested with blight bacteria were a source of primary inoculum, and 14% of commercial navy bean seed lots were so contaminated. Surface populations of Xp and Xpf ranged from 0 to 4 104 bacteria per seed; minimal populations of 103104 bacteria per seed were required for production of infected plants under field conditions. Symptomless seeds internally contaminated with Xp or Xpfwere identified as potential primary inoculum sources. Seeds with visible symptoms always were associated with visibly infected pods and pod infection resulting from systemically borne bacteria often caused hairline suture lesions which are difficult to detect.

Additional keywords: Phaseolus vulgaris.