Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2012
Publication Date: 7/27/2012
Citation: Kim, K., Unfried, J.R., Hyten, D.L., Frederick, R.D., Hartman, G.L., Nelson, R.L., Song, Q., Diers, B.W. 2012. Molecular mapping of soybean rust resistance in soybean accession PI 561356 and SNP haplotype analysis of the Rpp1 region in diverse germplasm. Theoretical and Applied Genetics. 125:1339-1352. Interpretive Summary: Phakopsora pachyrhizi is an obligate fungal pathogen that causes the foliar disease known as Asian soybean rust (SBR). Due to the genetic diversity within the pathogen population, it is important to identify new sources of resistance in soybean. The soybean accession PI 561356 was found to be resistant to specific isolates of the pathogen, and the SBR resistance gene in this line was mapped to a region on chromosome 18 that also contains the SBR resistance gene Rpp1. Comparison of 33 North American soybean ancestors using molecular markers, revealed that four belong to a group that share markers in common with PI 561356. This information will be useful to distinguish whether resistance gene(s) from new sources of SBR resistance are new or previously identified genes.
Technical Abstract: Soybean rust (SBR), caused by Phakopsora pachyrhizi Sydow, is one of the most economically important and destructive diseases of soybean [Glycine max (L.) Merr.] and the discovery of novel SBR resistance genes is needed because of diversity in the pathogen. The objectives of this research were to map SBR resistance in plant introduction (PI) 561356 and to identify single nucleotide polymorphism (SNP) haplotypes within the Rpp1 region on soybean chromosome 18. One-hundred F2:3 lines derived from a cross between PI 561356 and the susceptible experimental line LD02-4485 were genotyped and phenotyped for resistance to P. pachyrhizi isolate ZM01-1. The segregation ratio of reddish brown versus tan lesion type in the population supported that resistance was controlled by a single dominant gene and the gene was mapped to a 1 cM region on soybean chromosome 18 which corresponds to the same interval that the SBR resistance gene Rpp1 maps. A haplotype analysis of diverse germplasm across a 213 kb interval that included Rpp1 revealed 21 distinct haplotypes of which four haplotypes were present among five SBR resistance sources that have a resistance gene in the Rpp1 region. Four major North American soybean ancestors belong to the same SNP haplotype as PI 561356 and seven belong to the same haplotype as PI 594538A, the Rpp1-b source. There were no North American soybean ancestors belonging to the SNP haplotypes found in PI 200492, PI 587886 or PI 587880A.