Pyramiding novel genes for resistance to ascochyta blight from Pisum fulvum into field pea through molecular breeding

Ascochyta blight caused by Mycosphaerella pinodes (MP) is the most important pea disease in Canada and most pea growing regions in the world, often causing serious yield losses. Genetic resistance to ascochyta blight accumulated through two decades of breeding reduces disease severity, however, under cool, wet conditions, the resistance is not sufficient to prevent economic losses.  Some accessions of Pisum fulvum, a wild relative of field pea, possess a high level of resistance to ascochyta blight. This project was designed to initiate a long-term strategy for enhancement of ascochyta blight resistance in pea using an integrated genetic improvement approach through interspecific hybridization, careful phenotyping and molecular genotyping.

P. fulvum and several P. sativum subspp. elatius, transcaucasicum,  asiaticum, arvense and abyssinicum accessions obtained from USDA, Pullman, WA and IFAPA, Spain were evaluated.  Based on greenhouse and field experiments, 4 wild accessions namely, PI 344538 (P. sativum ssp. elatius), PI 560061 (P. fulvum), W6 15017 (P. fulvum) and P 651 (P. fulvum) were identified with substantially greater resistance than cultivar checks.  These accessions were crossed with the susceptible check cultivar Alfetta (P. sativum) and ‘inter-crosses’ were made among the four wild accessions to pyramid genes for resistance.  Crossed populations are currently in the F₄ generation, and intercross populations are in the F₃ generation. F₆ recombinant inbred lines (RILs) generated using single seed descent from one or more of the four crossed populations, and F₂-derived F₄ families from the six intercross populations will be evaluated for ascochyta blight resistance in the field in summer 2012. RILs will be used for quantitative trait locus (QTL) analysis to identify markers for resistance. To obtain a preliminary indication of ascochyta blight resistance, populations were developed from backcrosses between F₁ (wild parent × Alfetta) X Alfetta. These backcrossed populations (BC₁F₁) along with parents, F₁ and F₂-derived F₃ families will be tested for resistance in the greenhouse in early 2012. Germplasm derived from introgression of improved ascochyta blight resistance from the wild pea accessions will serve as a resource to pea breeders attempting to increase durability of resistance and increase yield potential.