Resistance Against the Existing and Emerging Pathogens and : A Case of Commonalities or Total Discrepancy?

Powdery mildew on (grass pea) is commonly caused by , the causal agent of pea powdery mildew. could also pose an additional threat to grass pea, as it does to pea (). In order to understand the potential threat and the availability of resistance sources, the response to both pathogens was analyzed on a worldwide germplasm collection of 189 grass pea accessions. Infection type and disease severity (DS) of grass pea accessions, independently inoculated with and were evaluated under controlled conditions. A wide range of responses were detected, with the previously uncharacterized partial resistance to in grass pea detected less frequently and uncorrelated with partial resistance against . To test for the lack of correlation at the genetic level, an exploratory association mapping study was undertaken by statistically combining grass pea collection DS scores against both pathogens, with 5,651 previously screened genotype-by-sequencing-based single nucleotide polymorphisms (SNP). Mostly different genetic regions in grass pea were identified as being associated with the response to and , anticipating an independent genetic basis that requires further validation in larger germplasm collections, with higher SNP densities. This study proposes common and unique partial resistance components against two different powdery mildews, implying the need for complementary approaches to introduce resistance to both pathogens into new grass pea varieties. The identified sources of resistance and predicted genomic targets will assist in breeding for resistance to multiple powdery mildews.