Rps8, A New Locus in Soybean for Resistance to Phytophthora sojae

Phytophthora root and stem rot caused by Phytophthora sojae M.J. Kaufmann & J.W. Gerdemann (=Phytophthora megasperma Drechs. f. sp. glycinea T. Kuan & D.C. Erwin) is the second leading cause of yield loss in soybean [Glycine max (L.) Merr.] in the USA. Currently, seven loci for resistance with 13 alleles have been identified in soybean. Populations of P. sojae exist in many soybean production regions that cause disease on plants with many, if not all, of these genes. Consequently, the need for new resistance loci is great. A number of plant introductions (PIs) from South Korea were identified in an earlier study that may contain novel resistance loci. The objectives of this project were to identify the allele(s) for resistance to P. sojae present in PI399073 and to map these allele(s) to a linkage group. PI399073 was crossed with ‘Williams’ and ‘S 19‐90’ to develop populations. These populations were assayed for disease resistance, single sequence repeats (SSR), restriction fragment length polymorphisms (RFLP), and isozyme markers. A new Phytophthora resistance locus, Rps8, was mapped to MLG (major linkage group) A2 in two different crosses with PI399073. This is the first locus for Phytophthora resistance that has been identified on MLG A2.