Population Genetic Structure of Apple Scab (Venturia inaequalis (Cooke) G. Winter) in Iran

The population genetic structure of 278 Venturia inaequalis isolates, collected from different apple cultivars of eighteen different provinces in Iran, was investigated using 22 polymorphic microsatellite markers. Analysis of molecular variation, Bayesian clustering and Nei's genetic distance analyses based on 88 microsatellite alleles indicated substantial levels of gene flow among the collection sites. Ninety three percent of the variation was observed among the individuals within the populations and only 7% variation was observed among the populations. Structure analysis grouped the isolates into two populations. Maximum number of pathogen genotypes (44) was observed in the North of Iran that grows various different apple cultivars. Investigation on the variation of the pathogen on different cultivars in the North of Iran suggested a significant differentiation of the pathogen populations between wild apple and commercial cultivars. During sampling, varying ranges of scab infection were observed on various apple cultivars in forests, monoculture and mix orchards. Wild type apple (Malus orientalis) along the Caspian Sea Coast had the most infection in comparison with the Iranian endemic and commercial cultivars. Based on the genetic analysis and host tracking scenario of the pathogen, it was presumed that Iran could potentially be the center of origin of V. inaequalis, which requires further detailed studies with isolates collected from different parts of central Asia and world for confirmation.