Map location of the Rpp1 locus that confers resistance to soybean rust in soybean

Soybean rust (SBR), caused by Phakopsora pachyrhizi, was first discovered in North America in 2004 and has the potential to become a major soybean [Glycine max (L.) Merr.] disease in the USA. Currently, four SBR resistance genes have been identified but not mapped on the soybean genetic linkage map. One of these resistance genes is the Rpp1 gene, which is present in the soybean accession PI 200492. The availability of molecular markers associated with Rpp1 will permit marker-assisted selection and expedite the incorporation of this gene into U.S. cultivars. We compared simple sequence repeat (SSR) markers between 'Williams 82' and the BC5 Williams 82 isoline L85-2378, which contains the Rpp1 resistance allele from the soybean accession PI 200492, for candidate regions that might contain Rpp1. One candidate region was found with the SSR marker BARC_Sct_187 on linkage group G. A population of BC6F2:3 lines segregating for the Rpp1 resistance locus was genotyped in this region on linkage group G followed by inoculation with the P. pachyrhizi isolate India 73-1 in the USDA-ARS Biosafety Level 3 Plant Pathogen Containment Facility at Ft. Detrick, MD. The Rpp1 gene was mapped between SSR markers BARC_Sct_187 and BARC_Sat_064 on linkage group G.