Three Novel er1 Alleles and Their Functional Markers for Breeding Resistance to Powdery Mildew (Erysiphe pisi) in Pea.

Powdery mildew caused by Erysiphe pisi DC is a global notorious disease on peas. Deploying resistance pea cultivars is the most efficient and environmentally friendly method for disease control. This study focuses on revealing the resistance genes in three pea germplasms and developing their functional markers for resistance breeding. The identification of resistance genes involved genetic mapping and the sequencing of the pea mildew resistance locus O homolog PsMLO1 gene. To confirm the heredity of three resistant germplasms, they were crossed with susceptible cultivars to generate F₁, F₂, and F_2:3 populations. The F₁ generation exhibited susceptibility to E. pisi, whereas the segregation patterns in subsequent generations adhered to the 3:1 (susceptible: resistant) and 1:2:1 (susceptible homozygotes: heterozygotes: resistant homozygotes) ratios, indicating that powdery mildew resistance was governed by a single recessive gene in each germplasm. Analysis of er1-linked markers and genetic mapping suggested that the resistance genes could be er1 alleles in these germplasms. The multiple clone sequencing results of the three homologous PsMLO1 genes showed they were novel er1 alleles, named er1-15, er1-16, and er1-17. The er1-15 and er1-16 were caused by 1-bp deletion at position 335 (A) and 429 (T) in exon 3, respectively, whereas er1-17 was caused by a 1-bp insertion at position 248 in exon 3, causing a frame-shift mutation and premature termination of PsMLO1 protein translation. Their respective functional markers, kompetitive allele-specific PCR (KASP)-er1-15, KASP-er1-16, and KASP-er1-17, were successfully developed and validated in respective mapping populations and pea germplasms. These results provide valuable tools for pea breeding resistance to E. pisi.