The NPGS Sudan sorghum germplasm collection reveals a novel cluster of R genes associated with rust resistant

Leaf rust, caused by the obligate fungal pathogen Puccinia purpurea, poses a serious threat to sorghum [Sorghum bicolor (L.) Moench] production leading to significant yield losses and undermining its values as renewable fuel crop. In this study, the United States Department of Agriculture-Agriculture Research Service, National Plant Germplasm System (NPGS) Sudan core collection was evaluated for rust-resistant response across four tropical environments. The analysis identified 18 accessions with rust resistant, among which four accessions (PI 568621, PI 569393, PI 570548, and PI 570974) consistently showed no rust pustules across all environments. Genome-wide association analysis led to the identification of a 57 kbp genomic region on chromosome 8 that encompasses a cluster of five homologous R genes. The resequencing analysis of the first exon from one candidate gene (Sobic.008G178200) found 61 point mutations that generate seven haplotypes. The high homology of these five genes and seven haplotypes indicates that this cluster might be acting as a single locus (Rp2) against P. purpurea. Comparative genome analysis found that the orthologs of Rp2 locus in maize (Zm00001d023311) are associated with the resistant response to Puccinia polysora, the causal agent of southern corn rust and in rice (Os12G29690), with resistance to the brown planthopper (Nilaparvata lugens). The introgression of the Rp2 locus into elite varieties or the inclusion of top-performing Sudanese tropical accessions in pre-breeding germplasm can accelerate the development of improved sorghum germplasm with durable rust resistant.