Two Novel er1 Alleles Conferring Powdery Mildew ( Erysiphe pisi ) Resistance Identified in a Worldwide Collection of Pea ( Pisum sativum L.) Germplasms

Powdery mildew caused by DC. severely affects pea crops worldwide. The use of resistant cultivars containing the gene is the most effective way to control this disease. The objectives of this study were to reveal alleles contained in 55 -resistant pea germplasms and to develop the functional markers of novel alleles. Sequences of 10 homologous cDNA clones from each germplasm accession were used to determine their alleles. The frame shift mutations and various alternative splicing patterns were observed during transcription of the gene. Two novel alleles, -8 and -9, were discovered in the germplasm accessions G0004839 and G0004400, respectively, and four known alleles were identified in 53 other accessions. One mutation in G0004839 was characterized by a 3-bp (GTG) deletion of the wild-type cDNA, resulting in a missing valine at position 447 of the PsMLO1 protein sequence. Another mutation in G0004400 was caused by a 1-bp (T) deletion of the wild-type cDNA sequence, resulting in a serine to leucine change of the PsMLO1 protein sequence. The -8 and -9 alleles were verified using resistance inheritance analysis and genetic mapping with respectively derived F and F populations. Finally, co-dominant functional markers specific to -8 and -9 were developed and validated in populations and pea germplasms. These results improve our understanding of resistance in pea germplasms worldwide and provide powerful tools for marker-assisted selection in pea breeding.