Influence of Soybean Genotype on Rate of Seed Maturation and Its Impact on Seedborne Fungi. L. D. Ploper, Former Graduate Research Assistant, Agricultural Research Service, U.S. Department of Agriculture, and Associate Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. T. S. Abney, and K. W. Roy. Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, and Associate Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; and Professor, Department of Plant Pathology and Weed Science, Mississippi State University, Mississippi State 39762. Plant Dis. 76:287-292. Accepted for publication 26 October 1991. 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, 1992. DOI: 10.1094/PD-76-0287.

Soybean (Glycine max) maturation rate, measured as the length or duration of late-season growth stage intervals and rate of moisture loss, was studied in a diverse group of soybean genotypes (plant introductions and adapted cultivars) to determine the role of plant and seed dry down on Phomopsis spp. and Cercospora kikuchii. A modified scale for late-season growth stages was developed and used to identify pod and seed maturation intervals after physiological maturity (R7₁, R7₂, and R7₃, identified by 1, 25, and 50% of all pods with mature pod color, respectively). Length of the R7₁–R8 period during major pod and seed dry down was associated consistently with the incidence of seed infection. Among genotypes with near-identical maturities, soybeans resistant to seedborne diseases had shorter R7₁–R8 intervals and a greater rate of moisture loss than susceptible soybeans. Incidence of pod infection by Phomopsis spp. or C. kikuchii was similar for soybean entries that matured under similar environmental conditions, regardless of their seed susceptibility under natural field conditions or to inoculation with P. sojae or C. kikuchii. Only susceptible genotypes showed a rapid increase in seed infection between R7₁ and R8, when pod and seed moisture decreased from 30–35% to 15–18%.