Rps8 maps to a resistance gene rich region on soybean molecular linkage group F

Phytophthora root and stem rot caused by Phytophthora sojae M.J. Kaufmann & J.W. Gerdemann is a serious disease of soybean [Glycine max (L.) Merr.] worldwide. Recently, a new locus for resistance to P. sojae, Rps8, was identified and mapped in two small soybean populations. The objective of this study was to verify the genomic location of Rps8 in a larger population. One hundred thirty-eight F(2:3) families from a cross between 'Williams' (rps8/rps8) x PI 399073 (Rps8/Rps8) were genotyped by simple sequence repeat (SSR) and restriction fragment length polymorphism (RFLP) markers. From this set of families, 138 and 69 were phenotyped with P. sojae races 1 and 25, respectively. The segregation ratio for each race fit a 3:1 resistant:susceptible, confirming that Rps8 segregated as a single dominant gene. On the basis of linkage analysis with SSR and RFLP markers, Rps8 was located on molecular linkage group F in this population. This region of the soybean genome contains numerous other resistance gene loci as well as pathogen and pest resistance QTL.