A novel susceptibility locus to Erysiphe necator (SEN2) identified by genetic mapping of automated microscopy computer vision data in grapevines.

Powdery mildew, caused by the fungus Erysiphe necator, is one of the primary causes of grape yield loss across the globe. While numerous resistance loci have been identified in various grapevine species, the genetic determinants of susceptibility to E. necator remain largely unexplored. Understanding the genetics of susceptibility for pathogenesis is equally important for developing durable resistance grapevines against this pathogen. To identify these factors in Vitis interspecific hybrid 'Chambourcin', a controlled leaf disc assay was conducted for two years using an automated microscopy phenotyping system with 273 F1 genotypes from a cross of 'Chambourcin' and V. vinifera 'Cabernet Sauvignon'. Additionally, a high-resolution linkage map using the same number of 'Chambourcin'-derived hybrids was constructed with 355 simple sequence repeats (SSR) and 1,394 RNaseH2-dependent amplicon sequencing (rhAmpSeq)-derived haplotype markers that clustered into 19 linkage groups. A quantitative trait locus (QTL) analysis identified a susceptibility locus (here named Sen2) on linkage group (LG) 7 explaining 8.90 % - 12.57 % of the total phenotypic variance. The markers associated with this susceptibility locus were used to identify 78 accessions in the USDA-ARS cold hardy Vitis collection at Geneva, NY that carry Sen2 and can be used to selectively exclude susceptible progenies. Additionally, 6 accessions carry the alternative haplotype encoding recessive resistance and can be used for resistance breeding. The identification of powdery mildew susceptibility loci is crucial for identifying genes that could be targeted for gene knock-out, gene editing, RNA interference (RNAi), or selection among breeding genotypes to enhance sustainable protection against pathogens.