Screening the Soybean Nested Association Mapping (SoyNAM) Parents for Resistance towards isolates of Phytophthora sojae, Fusarium graminearum, and species of Globisporangium

The Soybean Nested Association Mapping (SoyNAM) populations were developed from 40 parents and have been used to map genes underlying complex traits such as yield and disease resistance. Soil borne pathogens that affect soybean seed and seedlings result in significant losses due to reduced stands and costs associated with replanting. This study compared the response of these 40 SoyNAM parent genotypes to seed- and seedling-rot pathogens, Fusarium graminearum, Phytophthora sojae, Globisporangium ultimum var. ultimum, G. ultimum var. sporangiiferum, and G. irregulare groups 1, 2 and G. cryptoirregulare. None of the parental genotypes conferred high levels of resistance to F. graminearum nor G. ultimum var. sporangiiferum. Of the 40 parental genotypes, 15 were resistant to P. sojae OH1 (vir 7) indicating they contain Rps genes while the remaining (including the common parent IA 3023) do not have Rps genes. Based on inoculations with known P. sojae pathotypes, Rps1c was the most common followed by Rps1a as both Rps genes confer resistance to isolates OH4 (vir 1a, 1c, 7) and OH25 (vir 1a, 1b,1c, 1k, 7). Eight of the SoyNAM parents had higher levels of partial resistance to P. sojae than Conrad (cultivar with moderate resistance). There was moderate resistance to G. ultimum var ultimum among the 40 parents and to G. irregulare subpopulations among the 6 parents that were evaluated. The SoyNAM parental lines and populations are an excellent resource available for soybean breeders to advance the development of new cultivars with improved resistance to some soilborne pathogens.