荔枝矮化性状鉴定评价及其遗传规律和QTL定位研究

Dwarf culture is an important cultivation model in modern fruit management. Utilization of dwarf varieties is a principal approach to realize the dwarf cultivation, however, there is few dwarf litchi cultivars which have been breeded and used effectively, and the current production of litchi cultivation usually adopts heavy pruning to control the tree height, which not only pay enormous labor costs but also cause more consumption of water-fertilizer. In order to guide the innovation and utilization of dwarf varieties of litchi, the technical standards for the identification and evaluation of litchi dwarf traits would be established and optimized，and the genetic characteristics of dwarfing traits in litchi would be revealed. This research will be carried out in two ways: The first, large scale identification and evaluation of germplasm of litchi dwarf related traits, more than 200 germplasm would be evaluated and classificated, find out and verify the important traits association dwarf phenotype, and establish technical standards for rapid identification of litchi dwarfing traits. The second, the cross-population of 258 F1 hybrid progenies between a dwarf litchi cultivar ‘Ziniangxi’ as female parent and a tall culvivar ‘Feizixiao’ as male parent are used to study and reveal genetic mechanism of dwarf related traits, and the Reduced-representation sequencing approach will be used to build high density of genetic linkage map and location of quantitative trait loci for dwarf traits. The implementation of this research will provide the theoretical support and practical reference for litchi dwarf varieties breeding and application, and also help to enrich the dwarfing mechanism research of fruit trees.

矮化栽培是现代化果园管理的重要栽培模式，矮化品种或砧木的利用是实现矮化栽培的主要途径。然而，荔枝矮化品种尚缺乏有效培育和利用，通常采用重修剪方式以控制株高，往往需投入更多劳动力和肥水药等管理成本。为建立和优化荔枝矮化性状鉴定评价技术标准，揭示矮化性状遗传规律，指导开展荔枝矮化资源发掘、评价和创新利用，本项目拟从两个方面开展研究，一是以常规方法大规模评价荔枝矮化相关性状，对超过200份的种质矮化程度进行评价分级，筛选矮化重要关联性状并进行验证，建立荔枝矮化性状快速准确的鉴定与评价分级新技术；二是以矮化品种‘紫娘喜’和乔化品种‘妃子笑’杂交得到的258份子代为研究材料，基于简化基因组测序技术构建高密度遗传图谱，研究矮化及其关联性状的遗传分离特性，并对矮化性状进行QTL定位，深入揭示矮化性状的遗传机制。该项目的实施，将为荔枝矮化资源利用提供理论基础和实践参考，并有助于丰富果树矮化机理研究成果。

本项目系统开展了荔枝矮化性状鉴定评价、相关基因的筛选、遗传分离规律及QTL定位等工作，获得的主要研究内容及结果如下：.（1）提出了荔枝矮化指数（D值）的概念和计算公式，建立了基于矮化指数判定荔枝矮化级别的标准，并对120份荔枝资源矮化特性进行了评价分级；明确了枝皮率与枝梢直径呈现显著性负相关，相关系数达到了-0.69，在枝梢直径相近的情况下，不同品种之间枝皮率没有显著性差异，认为枝皮率不适宜作为荔枝矮化性状评价的关键指标。.（2）以‘妃子笑’和‘紫娘喜’的叶片和顶芽为材料，通过RNA-Seq测序比较矮化与乔化品种之间相关基因的差异表达情况，重点分析了42个植物激素信号转导途径和69个能量代谢途径中涉及的差异基因，将3个LcGA2oxs转入烟草进行过表达分析，发现LcGA2oxs在烟草中的超表达导致了转基因植株的明显矮化，说明LcGA2oxs具有一定的“致矮”功能，并可能参与到荔枝的矮化形成过程。.（3）以‘紫娘喜’为母本，‘妃子笑’为父本进行杂交，一共得到了325株杂交后代，对后代群体8个矮化相关性状进行鉴定评价，各表型的变异系数为11.50%～23.23%，中亲优势为-7.37%～18.68%，存在较明显的趋中遗传。由此可见，该杂交群体大小适中，目标性状分离显著，符合作图群体构建的相关要求。.（4）基于GBS技术进行简化基因组测序，鉴定得到了8,654,911个SNP标记，筛选出3027个SNP标记上图并分布在15个连锁群上，平均遗传距离为0.57 cM，图谱质量总体较高；检测到了37个QTL位点，可以解释8.0％至14.7％（平均值= 9.7％）的表型变异，在其中的32个QTL区域内发现126个候选基因，并获得了82个候选基因的注释信息以及50个双亲间有显著性差异表达的基因，这些基因在调控荔枝矮化方面的作用和机制还有待于进一步研究。