Mating Type Idiomorphs, Heterothallism, and High Genetic Diversity in , Cause of Peach Scab.

Scab (caused by ) is a major disease affecting peach in the eastern United States. The aims of the study were to characterize the mating-type loci in , determine whether they are in equilibrium, and assess the population genetic diversity and structure of the pathogen. The mating-type gene was identified in isolate JP3-5 in an available genome sequence, and the gene was PCR amplified from isolate PS1-1, thus indicating a heterothallic structure. Mating-type loci structures were consistent with those of other spp. ( and ): the mating-type gene is positioned between encoding a DNA lyase and a gene encoding a Pleckstrin homology domain. Primers designed to each of the mating-type genes and a reference gene were used as a multiplex PCR to screen a population ( = 81) of from various locations in the eastern United States. Mating types in five of the nine populations studied were in equilibrium. Among the 81 isolates, there were 69 multilocus genotypes. A population genetic analysis of the populations with >10 individuals (four populations) showed them to be genetically diverse. Linkage disequilibrium was found in five of nine populations with ≥4 isolates. A discriminant analysis of principal components indicated three genetic clusters, although extensive admixture was observed. Mating-type identification in provides a basis for understanding reproductive methods of the pathogen and can be a basis for further studies of the genetics of the peach scab pathogen.