Genetic Diversity and Conservation Challenges of The European Crab Apple (Malus sylvesrtis (L.) Mill.) in the Northwestern Balkans

Sažetak

This study investigates the genetic diversity and introgression dynamics of European crab apple (Malus sylvestris (L.) Mill., Rosaceae) populations in the northwestern Balkans. A total of 175 trees were analysed, including 157 putative wild individuals from 21 natural populations and 18 domesticated apples (M. ×domestica (Suckow) Borkh.) as out-groups. Genetic variation was assessed using ten nuclear microsatellite loci and Bayesian cluster analysis. The results revealed high allelic richness (average A = 25.2) and high genetic diversity (H_T = 0.76) with moderate population differentiation (F_ST = 0.14). Observed heterozygosity was generally lower than expected, suggesting potential effects of introgression and genetic drift. Bayesian assignment classified 60.58% of all sampled individuals as pure crab apples, 21.71% as hybrids, and 17.71% as domesticated apples. However, when excluding domesticated individuals, the proportion of pure crab apples within natural populations increased to 67.5%. Populations located in densely forested and sparsely populated regions exhibited higher genetic integrity, whereas those in fragmented and human-influenced landscapes showed increased hybridization. These findings highlight the role of human-mediated factors, such as supplemental feeding of wildlife, discarded apples, and the use of non-verified forest reproductive material, in facilitating gene flow from domesticated to wild apples. Conservation strategies should therefore favour genetically verified propagating material, protect populations with high genetic integrity, and mitigate human-induced pressures that promote hybridization between wild and domesticated apples.