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

Scab (caused by Venturia carpophila) is a major disease affecting peach in the eastern United States. The aims of the study were to characterize the mating-type loci in V. carpophila, determine whether they are in equilibrium, and assess the population genetic diversity and structure of the pathogen. The mating-type gene MAT1-1-1 was identified in isolate JP3-5 in an available genome sequence, and the MAT1-2-1 gene was PCR amplified from isolate PS1-1, thus indicating a heterothallic structure. Mating-type loci structures were consistent with those of other Venturia spp. (V. effusa and V. inaequalis): the mating-type gene is positioned between APN2 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 TUB2 were used as a multiplex PCR to screen a population (n = 81) of V. carpophila 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 V. carpophila 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.