Mapping of a soybean rust resistance in PI 594756 at the Rpp1 locus

Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi , is the main disease affecting soybean in Brazil. This study aimed at investigating and mapping the resistance of the PI 594756 to P. pachyrhizi , by using Bulked Segregant Analysis (BSA). The PI 594756 and the susceptible PI 594891 were crossed and the resulting F 2 and F 2:3 populations (208 and 1770 plants, respectively) were tested against ASR. Also, these PIs and differential varieties were tested against a panel of monosporic isolates. Plants presenting tan lesions were classified as susceptible ( S ) while plants presenting reddish-brown (RB) lesions were classified as resistant. DNA bulks were genotyped with Infinium BeadChips and the genomic region identified was further analyzed in the F 2 individuals with target GBS (tGBS). PI 594,56 presented a unique resistance profile compared to the differential varieties. The resistance was monogenic dominant; however, it was classified as incompletely dominant when quantitatively studied. Genetic and QTL mapping placed the PI 594756 gene between the genomic region located at 55,863,741 and 56,123,516 bp of chromosome 18. This position is slightly upstream mapping positions of Rpp1 (PI 200492) and Rpp1-b (PI 594538A). Finally, we performed a haplotype analysis in a whole genomic sequencing-SNP database composed of Brazilian historical germplasm and sources of Rpp genes. We found SNPs that successfully differentiated the new PI 594756 allele from Rpp1 and Rpp1-b sources. The haplotype identified can be used as a tool for marker-assisted selection (MAS).