新疆野苹果片段化分布种群遗传特征与保护策略研究

Malus sieversii is precious resource of wild fruit trees. It is fragmentally distributed in mountain ranges of Xinjiang and adjacent Central Asian countries. At present, this species is encountering an unprecedented crisis for survival. It is urgent to take reasonable and feasible actions to protect this important plant resource. Previous studies showed the indexes of genetic diversity can not efficiently identify priority protected areas of M. sieversii. Also, they have not clarified the phylogenetic relationships among these fragmented populations. However, the basis and key for analyzing the causes of fragmented distributions and developing effective conservation strategies is a further investigation on population genetic characteristics across the whole distribution range of M. sieversii. In the current project, we intend to collect 15 M. sieversii populations from Xinjiang and adjacent Central Asian countries. Firstly, based on the genome-wide SNP data, we will estimate demographic history and lineage divergence time. The evolutionary history and the causes of fragmented distributions will be clarified. Secondly, we will compare the differences of genetic diversity and structure among these 15 sampling populations. Status of the whole germplasm resources and conservation units will be identified. Thirdly, based on nSSR data, we will analyze the intra-population genetic structure with large sample size, the relationships between genetic diversity and effective population size and geographical area within six Chinese populations. The optimum size of in-situ conservation area for maintenance of germplasm diversity and ex-situ conservation measures for reserving special germplasm will be determined. These results will provide theoretical basis for establishing conservation network and germplasm resources nursery of M. sieversii. They also can provide new evidence to clarify the evolution of arid Central Asian plants.

珍稀野生果树新疆野苹果片段化分布于我国新疆与周边中亚山地。目前，它正面临着前所未有的生存危机，制定合理可行的保护措施已迫在眉睫。以前研究表明遗传多样性不能作为识别其优先保护种群的有效指标，且片段化种群间的遗传谱系关系尚未厘清。而解析片段化分布成因和制定有效保护策略的基础与关键是进一步探究整个分布区种群遗传特征。本项目拟收集我国及中亚分布15个新疆野苹果种群，基于简化基因组SNP数据，通过计算群体历史动态和谱系分化时间，阐明物种演化历史及片段化分布成因；通过比较种群间遗传多样性和遗传结构的差异，认清种质资源总体现状并确定保护单元；借助分子标记手段基于大样本数据解析我国6个种群内部遗传结构、计算遗传多样性与有效种群大小随空间面积变化趋势，确定维持种质多样性的最优化保护区面积和特殊种质迁地保护措施。预期成果将为规划新疆野苹果保护网络和建设种质资源圃提供依据；并为明晰中亚干旱区植物演化提供新证据。

新疆野苹果与现代栽培苹果具有最近的亲缘关系，是栽培苹果的主要祖先来源。目前，野苹果仅片段化分布在我国新疆和哈萨克斯坦、塔吉克斯坦、吉尔吉斯斯坦等国家的山地地区。野苹果国内外种群间遗传多样性和遗传结构已有研究较少，且该物种进化历史尚不清楚。本项目收集来自我国新疆、哈萨克斯坦、吉尔吉斯斯坦和塔吉克斯坦的15个野苹果种群，测定了简化基因组SNP标记数据，并测定了种群内部样本SSR标记数据。研究结果显示：①野苹果15个片段化种群被分成地理隔离和谱系分化的3个不同地理组。三个地理组之间的遗传分化发生在晚中新世，这一时期在全球变冷和山体隆升作用下中亚山地地区形成了较干旱的环境。中部组经历了有效群体大小增加的历史，其发生在第四纪间冰期时期。②野苹果的遗传变异受到经度梯度和环境异质性的影响。湿润环境地区为野苹果种群提供了避难所，并保留了较大的有效群体大小和高的遗传多样性。建议建立三个跨境保护单元，由于严酷的生境和小的有效群体，分布于边缘的塔城地区种群应该受到特别关注。③生境片段化和海拔梯度变化影响了野苹果种群内部景观遗传格局。对于生境片段化的巩留种群分析发现不同小群体间的遗传多样性存在差异，由于地理隔离效应作用，5个小群体可以划分为东西两个不同的遗传谱系。应当注重这些边缘小群体和不同遗传谱系的保育与保存。对于海拔落差大的额敏种群分析发现不同海拔样品间的遗传多样性存在差异，且呈现了低-高-低的单峰分布格局;低、中、高海拔地带之间的植株样品出现了显著的遗传分化。本项目研究成果可以为解析中亚孑遗落叶阔叶林演化历史提供新证据，并为新疆野苹果保护提供理论依据。