Genetic structure and historical demography of Malus sieversii in the Yili Valley and the western mountains of the Junggar Basin, Xinjiang, China

Malus sieversii, a wild progenitor of domesticated apple, is distributed in western Xinjiang of China, eastern part of Kazakhstan and Kyrgyzstan in Central Asia. To well understand the genetic structure and the historical demography of this important germplasm resource, we sampled 15 populations with 110 individuals of Malus sieversii from the Yili Valley and the western mountains of the Junggar Basin, Xinjiang, and sequenced two nrDNA fragments for these 110 individuals. Meanwhile, we modeled and compared species distributions under the current and the Last Glacial Maximum climatic conditions. The results showed that populations of M. sieversii from Xinjiang had low levels of genetic diversity and genetic differentiation. During the LGM period, populations of M. sieversii had lost their northern distributions in the western mountains of the Junggar Basin. M. sieversii has experienced a demographic expansion from the south of the Yili Valley to the north of the western mountains of the Junggar Basin during the warm interglacial epochs. Due to the high sensibility of M. sieversii to disturbance, we proposed more attention should be paid to the M. sieversii populations in the western mountains of the Junggar Basin.