Identification of a new soybean rust resistance gene in PI 567102B

Soybean rust (SBR) caused by Phakopsora pachyrhizi Syd. and P. Syd. is one of the most economically important diseases of soybean (Glycine max (L.) Merr.). Durable resistance to P. pachyrhizi is the most effective long-term strategy to control SBR. The objective of this study was to investigate the genetics of resistance to P. pachyrhizi in soybean accession PI 567102B. This accession was previously identified as resistant to SBR in Paraguay and to P. pachyrhizi isolates from seven states in the USA (Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina, and Texas). Analysis of two independent populations, one in which F(2) phenotypes were inferred from F(2)-derived F(3) (F(2:3)) families and the other in which F(2) plants had phenotypes measured directly, showed that the resistance in PI 567102B was controlled by a single dominant gene. Two different isolates (MS06-1 and LA04-1) at different locations (Stoneville, MS and Ft. Detrick, MD) were used to independently assay the two populations. Linkage analysis of both populations indicated that the resistance locus was located on chromosome 18 (formerly linkage group G), but at a different location than either Rpp1 or Rpp4, which were previously mapped to this linkage group. Therefore, the SBR resistance in PI 567102B appeared to be conditioned by a previously unreported locus, with an underlying single dominant gene inferred. We propose this gene to be designated Rpp6. Incorporating Rpp6 into improved soybean cultivars may have wide benefits as PI 567102B has been shown to provide resistance to P. pachyrhizi isolates from Paraguay and the US.