Evolution of the Eleusine subgroup of Pyricularia oryzae inferred from rearrangement at the Pwl1 locus.

ABSTRACT

Eleusine isolates (members of the Eleusine subgroup) of Pyricularia oryzae are divided into two groups, Ec-I and Ec-II, differentiated by molecular markers. A multilocus phylogenetic analysis and DNA fingerprinting suggested that Ec-I isolates are very close to Eragrostis isolates rather than Ec-II isolates. Infection assays revealed that Ec-II and Eragrostis isolates were exclusively virulent on finger millet and weeping lovegrass, respectively, whereas Ec-I isolates were virulent on both. The avirulence or virulence on weeping lovegrass perfectly corresponded to the presence or absence of an avirulence gene, PWL1; all Ec-II isolates carried an identical, functional PWL1, whereas none of Ec-I isolates or Eragrostis isolates carried it. A comparison of PWL1 flanking regions revealed that Ec-II isolates had a peculiar structure produced by an insertion (or translocation) of a DNA fragment carrying PWL1. Based on these results, a model was constructed which illustrated possible pathways to the establishment of the Eleusine subgroup.