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Predisposition to Seed Infection by Phomopsis sojae in Soybean Plants Infected by Soybean Mosaic Virus. P. R. Hepperly, Former graduate research assistant, Department of Plant Pathology, University of Illinois, Urbana 61801, Senior authorís present address: Department of Crop Protection, University of Puerto Rico, Mayaguez 00708; G. R. Bowers, Jr.(2), J. B. Sinclair(3), and Robert M. Goodman(4). (2)(3)(4)Graduate research assistant, professor, and associate professor, respectively, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 69:846-848. Accepted for publication 28 February 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-846.

Twenty-five soybean (Glycine max) lines were grown in the field and either inoculated at the primary leaf stage with the Illinois severe isolate of soybean mosaic virus (SMV) or not inoculated. In 20 lines, SMV inoculation reduced germination and increased seedborne incidence of Phomopsis sojae (Diaporthe phaseolorum var. sojae). Inoculation of Williams soybeans with SMV before or during flowering reduced germination and increased the incidence of P. sojae seed infection. Inoculation with SMV during pod development neither reduced germination nor increased seed infection by P. sojae. Regardless of the date of inoculation, Williams soybeans inoculated with SMV always yielded less than noninoculated plants. A. K. Harrow and Mansoy soybean plants grown in controlled-environment chambers were inoculated with SMV or P. sojae alone or in combination. The production of seeds with symptoms of P. sojae infection (moldy seeds) required both SMV and P. sojae inoculation. Soybean mosaic virus alone did not reduce seed germination or lead to production of damaged seed. When plants inoculated with SMV showed increased susceptibility to P. sojae, seed germination was reduced and damaged seed production was increased.

Additional keywords: Cercospora kikuchii, Colletotrichum dematium var. truncata, seedborne pathogens.