The ENU-induced powdery mildew resistant mutant pea (Pisum sativum L.) lines S(er1mut1) and F(er1mut2) harbour early stop codons in the PsMLO1 gene

Two pea (Pisum sativum L.) powdery mildew-resistant mutant lines, S(er1mut1) and F(er1mut2), were previously obtained by experimental chemical mutagenesis with ethylnitrosourea. Identification and subsequent analysis of the genomic sequence of the PsMLO1 gene revealed one single nucleotide mutation in each mutant line that leads to either a transversion or a transition, respectively, resulting in premature stop codons that drastically truncate the protein product of this gene in these two mutant lines. These results confirm the previous findings that PsMLO1 is the powdery mildew resistance gene er1. Only one additional mutation (transition) was observed in the S(er1mut1), downstream of the protein-truncating stop codon. Mutations were not identified in the intron regions of the gene. Specific molecular markers (cleaved amplified polymorphic sequences and sequence-tagged sites) were generated for the protein-truncating mutations, and these provide breeders with very efficient tools for marker-assisted selection when either of the two mutated lines are used in plant breeding programmes.