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Title: Genome-wide association mapping of partial resistance to Phytophthora sojae in soybean plant introductions from the Republic of Korea

item SCHNEIDER, RHIANNON - The Ohio State University
item ROLLING, WILLIAM - The Ohio State University
item Song, Qijian
item CREGAN, PERRY - Retired ARS Employee
item DORRANCE, ANNE - The Ohio State University
item MCHALE, LEAH - The Ohio State University

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2016
Publication Date: 8/11/2016
Citation: Schneider, R., Rolling, W., Song, Q., Cregan, P., Dorrance, A.E., Mchale, L.K. 2016. Genome-wide association mapping of partial resistance to Phytophthora sojae in soybean plant introductions from the Republic of Korea. BMC Genomics. 17:607. doi:10.1186/s12864-016-2918-5.

Interpretive Summary: Phytophthora root and stem rot disease negatively impacts soybean productivity across the USA. Some soybean varieties have resistance genes that reduce infection of specific Phytophthora races or strains. This specificity results in high selection pressure on the Phytophthora populations in the soil and allows the non-specified races to increase and cause new problems. By contrast, a less-specific type of partial resistance is controlled by multiple genes, each contributing a small level of resistance. Consequently, there is little selection pressure and the Phytophthora strains in the soil do not adapt as rapidly. In this study 1,395 soybean varieties from S. Korea were evaluated for partial resistance to Phytophthora root rot. Genetic analysis was performed to map partial resistance genes across the 20 pairs of soybean chromosomes. Sixteen DNA markers that defined Phytophthora root rot partial resistance traits were used to understand extent of resistance, root weight, shoot weight, and plant height. Molecular markers identified in this study can be used by breeders at universities, at companies and in government agencies to make soybeans resistant Phytophthora root rot and have other improved traits as well.

Technical Abstract: Phytophthora root and stem rot is one of the most yield-limiting diseases of soybean [Glycine max (L.) Merr], caused by the oomycete Phytophthora sojae. Partial resistance is controlled by several genes and, compared to single gene (Rps gene) resistance to P. sojae, places less selection pressure on P. sojae populations. Thus, partial resistance provides a more durable resistance against the pathogen. In previous work, plant introductions (PIs) originating from the Republic of Korea (S. Korea) have shown to be excellent sources for high levels of partial resistance against P. sojae. Resistance to two highly virulent P. sojae isolates was assessed in 1,395 PIs from S. Korea via a greenhouse layer test. Lines exhibiting possible Rps gene immunity or rot due to other pathogens were removed and the remaining 800 lines were used to identify regions of quantitative resistance using genome-wide association mapping. Sixteen SNP markers on chromosomes 3, 13, and 19 were significantly associated with partial resistance to P. sojae and were grouped into seven quantitative trait loci (QTL) by linkage disequilibrium blocks. Two QTL on chromosome 3 and three QTL on chromosome 19 represent possible novel loci for partial resistance to P. sojae. While candidate genes at QTL varied in their predicted functions, the coincidence of QTLs 3-2 and 13-1 on chromosomes 3 and 13, respectively, with Rps genes and resistance gene analogs provided support for the hypothesized mechanism of partial resistance involving weak R-gene.