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

isolates (members of the pathotype) of 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 isolates. EC-II and 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, . 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 . On the other hand, all EC-I and isolates were noncarriers of and shared a gene structure that should have predated the insertion of the -containing fragment. These results, together with phylogenetic analyses using whole-genome sequences, suggest that the -specific subgroup (EC-II) evolved through a loss of pathogenicity on weeping lovegrass caused by a gain of .