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Title: A novel phakopsora pachyrhizi resistance allele (rpp) contributed by PI 567068A

item KING, ZACHARY - University Of Georgia
item HARRIS, DONNA - University Of Georgia
item Pedley, Kerry
item Song, Qijian
item WANG, DECHUN - Michigan State University
item WEN, ZIXAING - Michigan State University
item BUCK, JAMES - University Of Georgia
item LI, ZENGLU - University Of Georgia
item BOERMA, H. ROGER - University Of Georgia

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2015
Publication Date: 12/24/2015
Citation: King, Z.R., Harris, D.K., Pedley, K.F., Song, Q., Wang, D., Wen, Z., Buck, J.W., Li, Z., Boerma, H. 2015. A novel phakopsora pachyrhizi resistance allele (rpp) contributed by PI 567068A. Theoretical and Applied Genetics. 129:517-534.

Interpretive Summary: Soybean rust, caused by the fungal pathogen Phakopsora pachyrhizi, is a detrimental disease to soybean and is a severe economic threat to soybean production, especially in the Americas. Host plant resistance is an important management strategy for the disease, as resistant soybean cultivars allow for minimal reliance on fungicides. To this end, the identification of genes that confer resistance against soybean rust enables breeders to develop soybean lines that can be grown in areas at risk for soybean rust epidemics. To date, ten resistance genes that protect soybean from specific isolates of the pathogen have been identified and mapped. These ten genes are located at six sites within the soybean genome. Recently, the soybean line PI567068A was demonstrated to possess a resistance gene that provides resistance to a unique set of P. pachyrhizi isolates. This discovery provided evidence that PI567068A may contain a novel resistance gene. Additional data indicates that this new resistance gene is located near a previously described resistance gene and therefore may be either a variation of that gene or a different gene altogether. These findings can be used by soybean breeders to incorporate the resistance gene from PI567068A into elite soybean germplasm.

Technical Abstract: Soybean rust (SBR) caused by the obligate, fungal pathogen Phakopsora pachyrhizi is an economic threat to soybean production, especially in the Americas. Host plant resistance is an important management strategy for SBR. The most recently described resistance to P. pachyrhizi (Rpp) gene is Rpp6 contributed by PI 567102B. Rpp6 was previously mapped to an interval over four million base pairs on chromosome 18. PI 567068A was recently demonstrated to possess a resistance gene near the Rpp6 locus, yet PI 567068A gave a differential isolate reaction to several global isolates of P. pachyrhizi. The goals of this research were to fine map the Rpp6 locus of PI 567102B and PI 567068A and determine whether or not PI 567068A harbors a novel Rpp6 allele or another allele at a tightly linked resistance locus. Linkage mapping in this study mapped Rpp6 from 5,916,005 to 5,961,229 bp (LOD score of 58.3); and the resistance from PI 567068A from 5,961,229 to 6,122,387 bp (LOD score of 4.4) (Wm82.a1 genome sequence). The two PIs shared the same haplotype window in these genomic regions. QTL peaks were 67,745 bp apart from one another as determined by the most significant SNPs in QTL mapping. The results of haplotype analysis demonstrated that PI 567102B and PI 567068A share the same haplotype in the resistance locus containing both Rpp alleles. Therefore the haplotype was designated as the Rpp6/Rpp[PI567068A] haplotype. The Rpp6/Rpp[PI567068A] haplotype identified in this study now exists as a tool to rapidly screen other genotypes that possess an Rpp gene(s) and can detect resistance at the Rpp6 locus when diverse germplasm is being screened.