Evaluation of early maturing soybean cultivars for partial resistance to Phytophthora sojae

Phytophthora root and stem rot, caused by Phytophthora sojae, is among the most damaging diseases of soybean in the United States. Race specific resistance has been effective in limiting losses to P. sojae. However, new races with virulence for available sources of resistance have appeared with increasing frequency over the past 40 years. Use of cultivars possessing partial resistance is a promising alternative for limiting yield loss to P. sojae. Little information is available on the resistance or partial resistance characteristic of early Maturity Group (MG) Plant Introductions (PIs) in MGs 000, 00, 0, 1. Our objective was to find early MG standard check cultivars that can be utilized in screening PIs for partial resistance. Using the inoculum layer method, we compared 24 cultivars in MGs 00-II and 4 standard check cultivars in MGs II and III for partial resistance to the combination of P. sojae races 7 and 25. Three of 24 early MG cultivars exhibited partial resistance equal to or greater than the check cultivar, Conrad (P > 0.05), and will be used in screening the early MG PIs.