Identification of the genetic bases conferring stem rust resistance in perennial ryegrass

Perennial ryegrass (<i>Lolium perenne</i>) is a key crop in grassland production, widely used as forage and turf. However, foliar diseases significantly affect seed yields, particularly stem rust (<i>Puccinia graminis</i> f. sp. <i>lolii</i>). Climate change and reduced pesticide use in Europe are expected to increase the risk of outbreaks. Developing durable resistant varieties offers a sustainable strategy for disease control.<br/>This study aims to characterize the natural variability of resistance to stem rust and identify the underlying genetic bases. A collection of 390 genotypes selected from diverse populations was screened for resistance to a Danish stem rust isolate by assessing pustule types, revealing completely resistant, partially resistant, and predominantly susceptible genotypes.<br/>A genome-wide association study (GWAS) identified a single resistance-associated locus on chromosome 7. Candidate genes within this locus were pinpointed using linkage disequilibrium analysis. To identify rare variants potentially involved in resistance but not detected by GWAS, two biparental mapping populations are being developed using four parental genotypes with contrasting resistance to three European and one American stem rust isolate.<br/>This study lays a foundation for understanding the molecular pathways of stem rust resistance and supports the development of resistant cultivars.