Field Pea () Germplasm Screening for Seedling Ascochyta Blight Resistance and Genome-Wide Association Studies Reveal Loci Associated with Resistance to and .

Ascochyta blight is a damaging disease that affects the stems, leaves, and pods of field pea () and impacts yield and grain quality. In Australia, field pea Ascochyta blight is primarily caused by the necrotrophic fungal species and . In this study, we screened 1,276 spp. germplasm accessions in seedling disease assays with a mix of three isolates of and 641 accessions with three mixed isolates of (513 accessions were screened with both species). A selection of three accessions with low disease scores for either pathogen, or in some cases both, were crossed with Australian field pea varieties PBA Gunyah and PBA Oura, and recombinant inbred line populations were made. Populations at the F and F generation were phenotyped for their disease response to and , and genotypes were determined using the diversity arrays technology genotyping method. Marker-trait associations were identified using a genome-wide association study approach. Trait-associated loci were mapped to the published genome assembly, and candidate resistance gene analogues were identified in the corresponding genomic regions. One locus on chromosome 2 (LG1) was associated with resistance to , and the 8 Mb genomic region contains 156 genes, two of which are serine/threonine protein kinases, putatively contributing to the resistance trait. A second locus on chromosome 5 (LG3) was associated with resistance to , and the 35 Mb region contains 488 genes, of which five are potential candidate resistance genes, including protein kinases, a mitogen-activated protein kinase, and an ethylene-responsive protein kinase homolog.