Evolution of an Eleusine-Specific Subgroup of Pyricularia oryzae Through a Gain of an Avirulence Gene.

Eleusine isolates (members of the Eleusine pathotype) of Pyricularia oryzae are divided into two subgroups, EC-I and EC-II, differentiated by molecular markers. A multilocus phylogenetic analysis revealed that these subgroups are very close to Eragrostis isolates. EC-II and Eragrostis isolates were exclusively virulent on finger millet and weeping lovegrass, respectively, while EC-I isolates were virulent on both. The avirulence of EC-II on weeping lovegrass was conditioned by an avirulence gene, PWL1. All EC-II isolates shared a peculiar structure (P structure) that was considered to be produced by an insertion (or translocation) of a DNA fragment carrying PWL1. On the other hand, all EC-I and Eragrostis isolates were noncarriers of PWL1 and shared a gene structure that should have predated the insertion of the PWL1-containing fragment. These results, together with phylogenetic analyses using whole-genome sequences, suggest that the Eleusine-specific subgroup (EC-II) evolved through a loss of pathogenicity on weeping lovegrass caused by a gain of PWL1.