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Growth Regulator Effects on Soybean Seed Maturation and Seedborne Fungi. T. S. Abney, Plant Pathologist, Crop Production and Pathology Unit, Agricultural Research Service, U.S. Department of Agriculture, Purdue University, West Lafayette, IN 47907 . L. D. Ploper, Former Graduate Research Assistant, Botany and Plant Pathology Department, Purdue University, West Lafayette, IN 47907. Plant Dis. 75:585-589. Accepted for publication 4 November 1990. 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, 1991. DOI: 10.1094/PD-75-0585.

Growth regulators (chlorflurenol [methyl 2-chloro-9-hydroxyfluorene-9-carboxylate], a morphactin, and ethephon [2-chloroethylphosphonic acid] or ethrel) were applied to soybeans (Glycine max) at midseason to alter the rate of maturation and incidence of seedborne fungi. Maturation rate, measured as the length of late-season growth stage intervals, was studied in diverse soybean genotypes to determine the role of plant and seed drydown on seed infection by Phomopsis spp. and Cercospora kikuchii. Chlorflurenol delayed maturity, extended the length of late-season growth stage intervals, and increased seed infection in entries susceptible or moderately resistant to seed diseases. Ethrel tended to hasten maturity, shorten late-season growth stage intervals, and decrease the percentage of seedborne fungi. Growth regulator effects on soybean genotypes that matured under the same environmental conditions indicate that initial levels of seed infection are directly related to the rate of pod and seed maturation (soybeans with low levels of seed infection have shorter drydown periods than those with high levels of seed infection). The growth stage interval consistently associated with seed infection was from physiological maturity (R71) to harvest maturity (R8). Modification of the R71R8 interval of susceptible and moderately resistant entries by means of growth regulators was directly associated with changes in levels of seed infection.