Abstract
Globally powdery mildew (PM) is one of the major diseases of the pea caused by Erysiphe pisi. Besides, two other species viz. Erysiphe trifolii and Erysiphe baeumleri have also been identified to infect the pea plant. To date, three resistant genes, namely er1, er2 and Er3 located on linkage groups VI, III and IV respectively were identified. Studies have shown the er1 gene to be a Pisum sativum Mildew resistance Locus 'O' homologue and subsequent analysis has identified eleven alleles namely er1-1 to er1-11. Despite reports mentioning the breakdown of er1 gene-mediated PM resistance by E. pisi and E. trifolii, it is still the most widely deployed gene in PM resistance breeding programmes across the world. Several linked DNA markers have been reported in different mapping populations with varying linkage distances and effectiveness, which were used by breeders to develop PM-resistant pea cultivars through marker assisted selection. This review summarizes the genetics of PM resistance and its mechanism, allelic variations of the er gene, marker linkage and future strategies to exploit this information for targeted PM resistance breeding in Pisum.