Characterizing the genetic architecture of nonhost resistance in barley using pathogenically diverse Puccinia isolates

Barley is an intermediate or near-nonhost to many cereal rust pathogens that infect grasses, making it a highly suitable model to understand the evolution and genetic basis of nonhost resistance (NHR) in plants. To characterise the genetic architecture of NHR in barley, we used the Oregon Wolfe Barley doubled haploid (DH) and Morex x SusPtrit RIL mapping populations. To elicit a wide array of NHR responses, we tested 492 barley accessions and both mapping populations with pathogenically diverse cereal rust isolates representing distinct formae speciales adapted to Avena, Hordeum, Triticum and Lolium spp.: P. coronata f. sp. avenae (Pca; oat crown rust pathogen) and f. sp. lolii (Pcl; ryegrass crown rust pathogen); P. graminis f. sp. avenae (Pga; oat stem rust pathogen) and f. sp. lolii (Pgl; the ryegrass stem rust pathogen); and P. striiformis f. sp. tritici (Pst; wheat stripe rust pathogen) and f. sp. pseudo-hordei (Psph; barley grass stripe rust pathogen). With the exception of Pcl and Pca, susceptibility and segregation for NHR was observed in the barley accessions and both mapping populations. QTLs for NHR were mapped on all seven chromosomes. NHR in barley to the heterologous rusts tested was due to a combination of QTLs with either or both overlapping and distinct specificities. Across both mapping populations, broadly effective NHR loci were also identified that likely play a role in host specialisation.