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Relationships Between Seedborne Soybean Fungi and Altered Photoperiod. J. R. Wilcox, Research geneticist, USDA-ARS and professor of agronomy, Purdue University, West Lafayette, IN 47907; T. S. Abney(2), and E. M. Frankenberger(3). (2)Research plant pathologist, USDA-ARS and associate professor of plant pathology, Purdue University, West Lafayette, IN 47907; (3)Research assistant, Department of Agronomy, Purdue University, West Lafayette, IN 47907. Phytopathology 75:797-800. Accepted for publication 26 February 1985. 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, 1985. DOI: 10.1094/Phyto-75-797.

The objective of this study was to evaluate seedborne pathogens of soybean cultivars in maturity groups I through IV when all cultivars were forced to mature as group II cultivars by manipulating photoperiod. Twenty cultivars were grown at Lafayette, IN, under a normal and an imposed 14-hr dark period. The extended dark period effectively shortened the maturation time for all cultivars. Mature seeds harvested from each cultivar under the two photoperiod treatments were plated on potato-dextrose agar to determine incidence of microorganisms in the seeds and to assess seed germination. Forced early maturation increased the incidence of seed infected by Phomopsis spp. from 5.3 to 31.5% and decreased seed germination from 89.4 to 61.4% across all cultivars. The results demonstrated that low incidence of Phomopsis spp. seed infection in late-maturing cultivars was not due to inherent resistance to these microorganisms but to escape from infection and disease development. Cercospora kikuchii and other microorganisms including Alternaria, Chaetomium, Fusarium spp., and bacteria occurred in seeds at very low levels and were not affected by photoperiod.

Additional keywords: Diaporthe spp., Glycine max, pod and stem blight.