Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2017
Publication Date: 10/7/2017
Citation: Childs, S.P., King, Z.R., Walker, D.R., Harris, D.K., Pedley, K.F., Buck, J.W., Boerma, H.R., Li, Z. 2017. Discovery of a seventh Rpp soybean rust resistance locus in soybean accession PI 605823. Theoretical and Applied Genetics. doi:10.1007/s00122-017-2983-4. Interpretive Summary: Soybean rust is an important disease of soybean, particularly in production regions with mild winters. Host plant resistance to rust could help reduce economic losses and contribute to more sustainable disease management. At least 10 different Rpp resistance genes have thus far been mapped to six independent loci (locations) in the soybean genome, but many of the soybean germplasm accessions that have been resistant in the United States have Rpp genes at only two of the loci. The Vietnamese accession PI 605823 was found to have an Rpp gene at a locus that has not previously been reported in the literature, and this gene has been given the name Rpp7. This identification of a unique and genetically independent resistance gene that could be combined with Rpp genes from other loci will provide soybean breeders with new options for developing lines and cultivars that should have broader and more durable resistance to soybean rust.
Technical Abstract: Soybean rust, caused by the obligate biotrophic fungal pathogen Phakopsora pachyrhizi Syd. & Syd, is a disease threat to soybean production in regions of the world with mild winters. Host plant resistance to P. pachyrhizi conditioned by Rpp genes has been found in numerous soybean accessions, and at least 10 Rpp genes or alleles have been mapped to six genetic loci. Identifying additional disease resistance genes will facilitate the development of soybean varieties with durable resistance. PI 605823, a plant introduction from Vietnam, was previously identified as resistant to U.S. populations of P. pachyrhizi in greenhouse and field trials. In this study, bulked segregant analysis using F2 populations derived from 'R00-1194F' x PI 605823 and 'Williams 82' x PI 605823 identified a genomic region associated with resistance to P. pachyrhizi isolates GA08 and GA12, which had been collected in the U.S. state of Georgia in 2008 and 2012, respectively. To further map the resistance locus, linkage mapping was carried out using single nucleotide polymorphism markers and phenotypic data from greenhouse assays with an F2:3 population derived from Williams 82 x PI 605823 and an F4:5 population derived from '5601T' x PI 605823. A novel resistance gene, Rpp7, was mapped to a 154-kilobase interval (Gm19: 39,462,291 - 39,616,643 Glyma.Wm82.a2) on chromosome 19 that is different from the genomic locations of any previously reported Rpp genes. This new gene could be incorporated into elite breeding lines to help provide more durable resistance to soybean rust.