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Effects of Soybean Stand Reduction and Phytophthora Root Rot on Yield. C. K. Moots, Former Graduate Research Assistant, Department of Agronomy, University of Illinois, and USDA-ARS, Urbana 61801. C. D. Nickell, and L. E. Gray. Professor, Department of Agronomy, and Associate Professor and Plant Pathologist, Department of Plant Pathology, University of Illinois, and USDA-ARS, Urbana 61801. Plant Dis. 72:900-904. Accepted for publication 15 May 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0900.

In this study, two near-isogenic soybean lines, Corsoy, susceptible, and L27, resistant to Phytophthora root rot (and the removal of plants to simulate the effects of stand reduction due to the disease) were used to examine how Phytophthora reduces yield. Results from experiments in two of the three environments tested indicated that factors other than stand reduction were contributing to yield reduction due to Phytophthora root rot. In the third environment, which had the lowest disease incidence, reduction in the number of plants per plot was the most critical factor influencing yield loss.