Detached leaf assays for resistance to crown rust reveal diversity within populations of Avena sterilis L.

Crown rust is the most widespread and damaging disease of oat (Avena species). Genetic resistance to the pathogen is the preferred method for crop protection but widespread deployment of limited numbers of major effect genes has promoted the rapid emergence and spread of pathogen races that are able to overcome these genes. Combining genes with even partial resistance may help develop durable cultivars which are less vulnerable to changes in pathogen virulence. Partial resistance is expected to be relatively common in populations of wild species where constant pathogen pressure encourages diversity in host resistance mechanisms, but it may be discarded in conventional screens for major gene resistance. Here, we have used a detached leaf assay to detect resistance to the crown rust pathogen, Puccinia coronata Cda. f.sp. avenae, in previously uncharacterised collections of the hexaploid wild oat relative Avena sterilis made by the Polish National Centre for Plant Genetic Resources (IHAR). Many of the accessions were collected in Morocco, the centre of diversity for the Avena genus. The detached leaf assessment allowed individual plants to be challenged with multiple pathotypes and their responses compared to 34 known differentials. Broad spectrum resistance was identified within accession PL 51855, which behaved as a single major locus on crossing to three cultivars. The locus provided resistance to over 50 rust pathotypes, a greater range than seen for any of the known Pc genes. Strong resistance was identified in other accessions, and heterogeneity in response within accessions was common. Several accessions show multiple partial resistance responses that may be of value for developing durable resistance in cultivars. As the sources of resistance in all but two differential lines were collected outside of Morocco, resistance in all accessions tested here are potentially novel. This study demonstrates that diversity within A. sterilis accessions collected in Morocco could be a very valuable source of resistance to crown rust, and provides new germplasm for use in resistance breeding programmes. Detached leaf assessment provides a valuable first step in the identification of promising candidates in complex genebank accessions