利用连锁作图与全基因组关联分析解析龙眼重要果实品质性状的等位变异

Longan (Dimocarpus longan Lour.) is an important tropical fruit in China. However, the lack of new longan varieties of high quality severely weakens Chinese trade competitiveness of the longan industry in the world. It is important to shorten longan breeding cycle when cultivating new varieties. An F1 mapping population of ‘Fengliduo’ בDawuyuan’ was created in 2002, and QTL mapping for some fruit quality traits of longan were studied, but these results cannot be applied directly in longan breeding. In this project, dissection of allelic variation of single fruit weight and soluble solids content of longan will be carried out based on linkage map and genome-wide association analysis. There are two parts in this project: (1) A high-density and high-precision genetic map will be constructed with SSR and SNP makers by using single fruit weight and soluble solids content widely separated cross population (190 sexual progenies) as the mapping population. This genetic map will be applied for QTL analysis; (2) Genome-wide association analysis will be employed to dissect single fruit weight and soluble solids content and identify the excellent allelic variation through utilizing a series of longan variety resource (220 varieties). Finally, the molecular mechanisms underlying allelic variation will be illustrated based on the QTL mapping and genome-wide association analysis results. The results will lay foundation for marker assisted selection (MAS) for longan quality improvement and provide potential breeding materials for cultivating new varieties.

优质龙眼新品种的缺乏严重削弱了我国龙眼产业在国内外贸易中的竞争力，如何快速培育优质新品种是当今我国龙眼育种中面临的重要问题。项目组2002年创建了‘凤梨朵’ב大乌圆’F1作图群体，对部分品质性状进行了QTL作图，但这些成果还不能直接应用于龙眼品质育种实践中。本项目拟采用连锁作图与全基因组关联分析相结合的策略，深入解析龙眼单果重与可溶性固形物含量的等位变异，项目分两部分进行：(1) 以190份F1分离群体为材料，利用SSR和SNP标记构建高密度、高精度遗传图谱，对龙眼单果重和可溶性固形物含量进行QTL分析；（2）以220份品种资源群体为材料，对单果重和可溶性固形物含量进行全基因组关联分析，确定优异的等位变异。整合连锁分析和全基因组关联分析的结果，获得准确丰富的信息，进一步揭示龙眼单果重和可溶性固形物含量的遗传基础，研究结果将为开展龙眼分子辅助选择加快优质龙眼培育提供材料基础和科学依据。

优质龙眼新品种的缺乏严重削弱了我国龙眼产业在国内外贸易中的竞争力，如何快速培育优质新品种是当今我国龙眼育种中面临的重要问题。本项目采用连锁作图与全基因组关联分析相结合的策略，对龙眼单果重与可溶性固形物含量的等位变异进行了解析。(1) 以190份‘凤梨朵’ב大乌圆’F1群体为材料，构建了高密度的遗传图谱，15条连锁群上包含8014个上图标记，总长度为2873.39cM，平均遗传距离为0.36cM。利用该图谱，采用MapQTL软件对单果重和可溶性固形物含量性状进行QTL定位。在LOD>3.0的阈值下，基于2017和2018年数据，鉴定出了20个QTL位点（区间），单果重的有16个，可溶性固形物含量的有4个,可解释表型变异率为 10.10-21.00%。（2）以220份品种资源群体为材料，对单果重和可溶性固形物含量进行全基因组关联分析。在阈值-log10p>5.01条件下检测到2个SNP位点与可溶性固形物含量显著关联，根据龙眼参考基因组信息，在SNPs上下游20kb范围内注释到有12个候选基因，整合QTL分析结果，结合龙眼参考基因组的注释信息及相关基因研究报道，最终找到3个参与调控龙眼可溶性固形物含量的关键基因。在阈值-log10p>6.01条件下共检测到24个SNP位点与单果重显著关联，根据龙眼基因组信息，在关联区段内共注释到有58个候选基因。整合QTL分析结果，找到了5个与龙眼单果重极显著相关的SNP位点。该项目将连锁作图的高效性和关联分析的精确性有机结合，解析了龙眼单果重和可溶性固形物含量的等位变异，为建立龙眼基因标记辅助选择育种技术快速培育优质龙眼新品种奠定了基础，同时也为其他木本植物的复杂性状研究提了供参考。