Genetic diversity and spatial genetic structure of Caucasian apple (Malus orientalis Uglitzk.) populations based on microsatellite markers for conservation strategy

An important tree in Eurasia, Malus orientalis Uglitzk. (Caucasian apple) provides ecological and economic benefits. To evaluate the genetic diversity of this species, we sampled 167 individuals from 20 populations across the Zagros Mountains (6 populations) and Hyrcanian forests (14 populations). We assessed six quantitative morphological traits and employed 26 microsatellite (SSR) markers, which revealed a total of 455 alleles in the wild apple populations, all of which were polymorphic. The markers revealed mean values for genetic diversity indices, including allelic richness (Ar = 0.21), private alleles (Ap = 0.65), expected heterozygosity (H_E = 0.74), and observed heterozygosity (H_O = 0.71). Our analyses identified three major genetic clusters and two significant genetic barriers among the studied populations. Estimations of gene flow indicated limited connectivity among M. orientalis populations in the Caucasus region, suggesting habitat fragmentation as a key factor shaping genetic structure. Based on genetic diversity assessments, two areas within the Hyrcanian forest (Siamarzkoh region, Tokestan region, Abesk region, Asalem region) and one in the Zagros forest (Sepedkoh region) were identified as priority regions for conservation efforts to protect this valuable species.