Mapping and confirmation of two genes conferring resistance to soybean rust (Phakopsora pachyrhizi Syd.) in the soybean line UG-5 (Glycine max)

Authors: PAUL, CHANDRA - University Of Illinois; Hartman, Glen; DIERS, BRIAN - University Of Illinois; Walker, David

Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2020
Publication Date: 9/9/2020
Citation: Paul, C., Hartman, G.L., Diers, B., Walker, D.R. 2020. Mapping and confirmation of two genes conferring resistance to soybean rust (Phakopsora pachyrhizi Syd.) in the soybean line UG-5 (Glycine max). Plant Breeding. p. 1-11. https://doi.org/10.1111/pbr.12854.
DOI: https://doi.org/10.1111/pbr.12854

Interpretive Summary: Soybean rust is one of the most important foliar diseases of soybean, particularly in tropical and subtropical production regions. The Ugandan cultivar UG-5 has had high levels of rust resistance in the United States as well as in Africa. Wider use of rust-resistant soybean cultivars would reduce production costs for growers in places like the southern United States and would decrease the need for fungicide applications to reduce yield losses to soybean rust. A genetic mapping study was conducted to identify the number and locations of rust resistance (Rpp) genes in UG-5 using two mapping methods and two independent mapping populations. Data from both populations indicated that UG-5 has one resistance gene at the Rpp1 locus on soybean chromosome 18 and another at the Rpp3 locus on chromosome 6. This confirms the locations implicated in an earlier study and led to the development of molecular markers tightly linked to the two genes. This information will be useful to soybean breeders interested in transferring the two Rpp genes into new, high-yielding cultivars for rust-prone production areas.

Technical Abstract: Soybean rust (SBR), caused by Phakopsora pachyrhizi, is an important foliar disease of soybean, particularly in tropical and subtropical production areas. Although resistant germplasm has been identified, the development of cultivars with broad and durable resistance is challenging due to pathogenic diversity and plasticity in fungal populations. The objective of this research was to investigate the number and genomic locations of SBR resistance (Rpp) genes in the Ugandan cultivar UG-5, which has shown resistance in the United States as well as in central and western Africa. Bulked segregant analysis detected two genomic regions in an F2 population and in an independent F2:3 population from crosses between ‘Williams 82’ and UG-5. Linkage mapping confirmed that a region detected on chromosome 18 is the location of the Rpp1 locus, and that another region on chromosome 6 is where the Rpp3 locus had previously been mapped. No evidence for additional segregating Rpp genes was found. The confirmation that resistance genes at the Rpp1 and Rpp3 loci provide UG-5 with a high level of resistance to U.S. isolates of P. pachyrhizi and the identification of tightly linked simple sequence repeat and single nucleotide polymorphism-based DNA markers provide an opportunity for soybean breeders to transfer two highly effective SBR resistance genes from the same parent into genetic backgrounds that yield well in targeted production areas.