Phylogeny of Venturia Species and Population Genetic Structure of V. inaequalis in Iran

Venturia genus includes important species such as Venturia inaequalis and V. pyrina causing scab and black spot on apple and pear, respectively. Eight hundred specimens from infected plants in 18 provinces of Iran were morphologically surveyed. Phylogenetic analysis of 18 isolates from nine host species based on sequence information of five genes (Actin-1, β-tubulin, EF-1α, gapdh, and ITS) showed host-specificity of Venturia with nine species (V. carpophila, V. circinans, V. eriobotryae, V. fraxini, V. geranii, V. inaequalis, V. oleaginea, V. pyracanthae and V. pyrina). V. eriobotryae and V. pyracanthae were two new combinations and V. circinans (Coleroa circinans) grouped with Venturia species. Population genetic structure analysis of 278 isolates of V. inaequalis (dominant species in Iran), from different apple cultivars, with 22 polymorphic microsatellites indicated substantial levels of gene flow among their collection sites. Ninety three percent of the variation was observed among individuals within two structured populations and only 7% variation was observed among the populations. Forty-four genotypes were observed in the North of Iran with significant pathogen population differentiation between wild apple and commercial cultivars. Varying ranges of scab infection were observed on apple cultivars in forests, monoculture and mixed orchards. Wild type apple along the Caspian Sea Coast had the most infection compared to the Iranian endemic and commercial cultivars. Genetic analysis and host tracking of the pathogen hinted Iran as the possible center of origin of V. inaequalis, which requires detailed studies with isolates from different parts of central Asia and world for confirmation.