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Title: Identification of unique genetic sources of soybean rust resistance from the USDA germplasm collection

item HARRIS, DONNA - University Of Georgia
item Kendrick, Mandy
item KING, ZACHARY - University Of Georgia
item Pedley, Kerry
item Walker, David
item Cregan, Perry
item BUCK, JAMES - University Of Georgia
item PHILLIPS, DANIEL - University Of Georgia
item LI, ZENGLU - University Of Georgia
item BOERMA, H. ROGER - University Of Georgia

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2015
Publication Date: 6/26/2015
Publication URL:
Citation: Harris, D.K., Kendrick, M.D., King, Z.R., Pedley, K.F., Walker, D.R., Cregan, P.B., Buck, J.W., Phillips, D.V., Li, Z., Boerma, H. 2015. Identification of unique genetic sources of soybean rust resistance from the USDA germplasm collection. Crop Science. DOI: 10.2135/cropsci2014.09.0671.

Interpretive Summary: Disease of soybean (Glycine max) due to the potential for severe yield losses. The disease now occurs in all major soybean-growing regions of the world including the continental United States, and in time the pathogen will likely adapt to overcome the few resistance genes that have been identified. To combat this threat it is important to identify new and unique sources of resistance from plant introductions (PIs) that can be introduced into commercial soybean cultivars. We identified seventy-five soybean rust-resistant PIs using field and greenhouse assays and these PIs were used to perform crosses for further analysis, which included mapping of the putative resistance genes within the soybean genome. Ultimately, several putative unique sources of resistance were identified which are being further characterized. These putative unique sources of resistance will be useful to soybean breeders working to combat the threat posed by soybean rust. Capitalizing on recent advances, a novel rapid and cost effective method of analysis was also evaluated as an additional tool for soybean breeders to identify unique genes for soybean rust resistance. The results of this study indicate that the novel analysis method will be a useful tool for soybean breeders and researchers seeking to integrate new sources of resistance into elite soybean cultivars. Such cultivars would be of utility in areas affected by this disease.

Technical Abstract: Soybean rust (SBR) is caused by the fungal pathogen Phakopsora pachyrhizi. Thus far, six rust resistance loci (Rpp1, 2, 3, 4, 5, and 6) have been reported. On the basis of field and greenhouse phenotyping assays between 2006 and 2011, we identified 75 SBR-resistant plant introductions (PIs). Crosses were made between these PIs and a susceptible elite soybean cultivar or breeding line. Bulked segregant analysis (BSA) was used to determine if the PI resistance genes mapped to a previously identified locus or to an unreported locus. Fifty two of these PIs mapped to the Rpp3 region on chromosome 6 of the soybean genome. A set of eight P. pachyrhizi isolates collected from different areas of the world were used to further characterize the resistant PIs for their phenotypic responses. Forty two of these 52 PIs reacted the same to the panel of isolates used as either PI462312 (the source of Rpp3) or Hyuuga (a natural pyramid of Rpp3 and Rpp5). Additionally, with the fine mapping of Rpp1, Rpp3, and Rpp4 and the recent availability of the SoySNP 50k Infinium Chip data on the USDA Soybean Germplasm Collection, we were able to use our BSA and isolate data on these PI’s to determine in retrospect how effective haplotype analysis would be in narrowing down the PIs to those accessions most likely to have a putatively unique source of resistance. Results from this verification process indicate that haplotype analysis is a useful tool. Thirty-seven of the 52 PI’s mapping to the Rpp3 region also had an identical haplotype to that of PI462312. In the future, a combination of these analyses and phenotyping efforts could prove useful in more rapidly narrowing down resistant PIs to only those with a high potential of carrying a unique resistance gene. We are currently working to map F2:3 populations of the PIs identified from this study that had putative unique sources of resistance to SBR.