Genome-wide association study identifies major rust-resistance loci in temperate sorghum

Abstract Leaf rust, caused by Puccinia purpurea , is a major constraint on sorghum [ Sorghum bicolor (L.) Moench] production. A total of 278 accessions from the sorghum association panel (SAP) were evaluated for rust severity on a 1–5 scale; where 1 indicates no rust pustules and 5 more than 66% of the leaf infected. Initial evaluations conducted in Mayaguez and Isabela, Puerto Rico in 2015 and 2022, respectively, identified 26 accessions with no rust pustules. These accessions were re-evaluated at Isabela, Puerto Rico in 2024, and 19 were confirmed as resistant across years (score < 1.50) including 10 that consistently exhibited complete absence of rust pustules. A genome-wide association analysis using 233,899 SNPs and the FarmCPU model was performed with average and binary resistant scores. Six loci associated with rust resistance were identified on chromosomes 1, 2, 5, 6, 8 and 9. The strongest association was a 33 Kb region on chromosome 8 detected with binary resistant score. This region contains four BURP-domains homologous genes ( Sobic.008G157500 , Sobic.008G157600 , Sobic.008G157700 , and Sobic.008G157800 ) and was designated Rp3 . These rust resistance accessions provide a valuable genetic resource for characterizing rust pathotype diversity, improving understanding of resistance mechanism, and to develop new sorghum germplasm.