Abstract
Anthropogenic and natural divergence processes in crop-wild fruit tree complexes are less studied than in annual crops, especially in the Caucasus, a pivotal region for plant domestication. We investigated anthropogenic and natural divergence processes in apples in the Caucasus using 26 microsatellite markers amplified in 550 wild and cultivated samples. We found two distinct cultivated populations in Iran, that were both genetically differentiated from Malus domestica, the standard cultivated apple worldwide. Coalescent-based inferences using approximate Bayesian computation showed that these two cultivated populations originated from specific domestication events in Iran. One of the Iranian clusters encompassed both cultivated and forest trees, suggesting that either farmers use of local wild apple for cultivation or that some forest trees represent feral cultivars. We found evidence of substantial wild-to-crop, crop-crop and crop-to-wild gene flow in the Caucasus, as has been previously described in apple in Europe and in fruit trees in general. In the Caucasus, we identified seven genetically differentiated populations of wild apple (Malus orientalis). Niche modeling combined with genetic diversity estimates indicated that these populations likely resulted from range changes during the last glaciation. This study identifies Iran as a key region in the evolution and domestication of apple and further demonstrates the role of wild-to-crop gene flow during fruit tree domestication. Our results support the view that domestication of fruit trees was likely a geographically diffuse and protracted process, involving multiple, geographically disparate, origins of domestication. We also highlight the impact of climate change on the natural divergence of a wild fruit tree and provides a base for apple conservation and breeding programs in the Caucasus.
Competing Interest Statement
The authors have declared no competing interest.
