LAUSR

Powdery mildew in Lathyrus sativus (grass pea), is commonly caused by Erysiphe pisi, the causal agent of pea powdery mildew. Erysiphe trifolii could also impose 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 E. pisi and E. trifolii, were evaluated under controlled conditions. Wide-range of responses was detected, with the previously uncharacterized partial resistance to E. trifolii in grass pea being less frequent and uncorrelated with partial resistance against E. pisi. To test for the lack of correlation at the genetic level, an exploratory association mapping study was undertook 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 associated with the response to E. trifolii and E. pisi, anticipating an independent genetic basis that needs 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 this multi powdery mildew-resistance breeding.