Genetic diversity and geographic distribution patterns of Malus landraces from 5 cultivated species under climate change in China

China is the largest center of genetic diversity of apple (Malus Mill.), with rich germplasm resources. In the process of evolution and domestication, a large number of apple landraces appeared, and they played a very important role before the introduction of modern cultivated apple varieties to China. However, the habitat of Malus landraces is under serious threat. In this study, 19 pairs of polymorphic simple sequence repeat primers were used to analyze the genetic structure and genetic relationships of Malus landraces and the potential distribution was predicted according to eight environmental variables using MaxEnt modeling. The results showed that the genetic variation of Malus landraces was high (Ho = 0.728 and He = 0.884), and the genetic differentiation was mainly distributed within respective populations and with almost no differentiation among populations. The five population groups were ranked, from highest genetic diversity level to lowest, as follows: Malus domestica subsp. chinensis > Malus prunifolia > Malus robusta > Malus asiatica > Malus micromalus. The 216 germplasms were divided into five groups based on Nei's genetic distance, whereas the Bayesian structure analysis categorized them into two groups. Population structure and principal coordinate analyses showed that Malus domestica subsp. chinensis, Malus asiatica and Malus prunifolia may be derived from similar genetic sources. In the modeling analysis, the cumulative contribution of temperature to the distribution of Malus landraces in suitable growth areas reached 66.1 %, and BIO4 (temperature seasonality) was identified as the major factor influencing the distribution of Malus landraces. Under four future emission scenarios, the potential distribution range of Malus landraces basically unchanged, but the total potential distribution area is projected to grow greatly over time and will tend to shift to higher latitudes.