| Summary: | Powdery mildew caused by <i>Erysiphe pisi</i> DC. severely affects pea crops worldwide. The use of resistant cultivars containing the <i>er1</i> gene is the most effective way to control this disease. The objectives of this study were to reveal <i>er1</i> alleles contained in 55 <i>E. pisi</i>-resistant pea germplasms and to develop the functional markers of novel alleles. Sequences of 10 homologous <i>PsMLO1</i> cDNA clones from each germplasm accession were used to determine their <i>er1</i> alleles. The frame shift mutations and various alternative splicing patterns were observed during transcription of the <i>er1</i> gene. Two novel <i>er1</i> alleles, <i>er1</i>-8 and <i>er1</i>-9, were discovered in the germplasm accessions G0004839 and G0004400, respectively, and four known <i>er1</i> alleles were identified in 53 other accessions. One mutation in G0004839 was characterized by a 3-bp (GTG) deletion of the wild-type <i>PsMLO1</i> 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 <i>PsMLO1</i> cDNA sequence, resulting in a serine to leucine change of the PsMLO1 protein sequence. The <i>er1</i>-8 and <i>er1</i>-9 alleles were verified using resistance inheritance analysis and genetic mapping with respectively derived F<sub>2</sub> and F<sub>2:3</sub> populations. Finally, co-dominant functional markers specific to <i>er1</i>-8 and <i>er1</i>-9 were developed and validated in populations and pea germplasms. These results improve our understanding of <i>E. pisi</i> resistance in pea germplasms worldwide and provide powerful tools for marker-assisted selection in pea breeding.
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