利用MAGIC群体解析陆地棉重要经济性状的遗传基础

Cotton is one of the important economic crops in China. Among the four cultivated species, upland cotton cultivars are widely cultivated because of its wide adaptability and high yield production. However, our country is not the origin place of cotton, the upland cotton cultivars are mainly derived from some basic cultivars introduced from the United States, which resulted in the narrow genetic diversity. Long-term directional selection makes genetic basis of upland cotton cultivars in our country very narrow; the further promotion space of cultivar traits is very limited. DNA marker research results on the genetic diversity also confirmed this phenomenon. Upland cotton breeding are now facing with serious "bottleneck effect" in China. The genetic dissection of important traits in upland cotton cultivars is very important to genetic improvement of this crop. However, the recent studies are mainly focused on populations derivred from biparents or few parents. The low polymorphism and the few alleles restrict the studies of genetic dissection of upland cotton. In order to better understand the genetic basis of important traits in upland cotton, our project team members developed a MAGIC (Multi-parent Advanced Generation Inter-Cross) population with 12 parents through several years of efforts. These parents include varieties with high yield, good fiber quality, resistance to fusarium wilt and verticillium wilt, and resistance to insects, which is an ideal population of study quantative traits in cotton. Based on this MAGIC population, our researches will focus the following contents: (1) with the aid of the high-density cotton genetic map constructed in our lab, and the RAD-seq sequencing, the genotype composition of the MAGIC population will be studied to understand the different parent's chromosome distribution; (2) combined with phenotype identified in multi enviroments, the genetic basis of different trait architecture will be analyzed; the effect of different alleles will be especially studied; (3) polymorphic molecular markers that can be directly used by other researchers will be provided; elite verities with many good trait characters will be identified through the field test and molecular marker assisted selection, which will be applied to breeding research.

陆地棉因其适应性广、产量高而被广泛种植。然而，我国不是棉花的起源地，我国培育的品种血缘非常狭窄。长期的定向选择使得我国陆地棉品种遗传基础很狭窄，品种性状进一步提升的空间非常有限，DNA标记的研究结果也验证了这一现象。陆地棉性状遗传基础的解析对于陆地棉的改良具有重要意义。然而，目前的研究多采用两亲本的作图群体。多态性低和等位基因少限制了陆地棉性状遗传基础的解析。为了更好的解析陆地棉性状的遗传基础，本项目组成员通过多年的努力，创造了12亲本的MAGIC群体。这些亲本包括高产、优质、抗枯萎病、耐黄萎病及抗虫性状优良的材料。本研究拟以该群体为研究对象，开展以下研究：（1）借助本课题组构建的高密度图谱和RAD-seq测序，研究该群体的基因型构成；（2）结合多环境的表型鉴定，剖析优良性状形成的遗传基础，着重解析不同等位基因的效应；（3）筛选公共多态性标记和综合性状好的优良品系，应用于育种研究。

棉花是我国重要的经济作物，为纺织业提供了纤维原料。陆地棉作为棉花的一个栽培种，因其适应性广、产量高而被广泛种植。通过分子生物学手段去解析陆地棉重要经济形状的遗传基础，对陆地棉的改良育种具有重要指导意义。传统方法中主要应用连锁分析和关联分析去定位相关性状的QTL（quantitative trait loci）。其中连锁分析主要基于双亲本的作图群体，而我国陆地棉品种遗传基础狭窄，多态性低、等位基因少，限制了其QTL检测效率。而关联分析则主要利用自然群体，在作图定位中，受到群体结构和LD（Linkage disequilibrium）衰减慢等因素影响，限制了其作图精度和准确度。为了更好地解析陆地棉性状的遗传基础，本研究挑选了8个遗传和表型丰富的亲本构建陆地棉MAGIC群体，群体包含960个株系。首先，设置合理的实验对该群体进行基因分型和表型鉴定。将MAGIC群体种植于三个地点两年共6个环境中考察了共14个重要的农艺性状，分析发现MAGIC群体具有丰富的表型变异。利用亲本从本实验室构建的高密度海岛棉-陆地棉种间遗传图谱上筛选多态性的SSR（simple sequence repeat）标记，总共获得并完成284对高质量的SSR标记对MAGIC群体的基因分型，利用基因分型的数据分析MAGIC群体的遗传构成，发现该MAGIC群体在亲本的基础上产生了更广泛的重组变异，遗传多样性高，没有明显的群体结构，而且LD衰减较快。然后，利用关联分析混合线性模型将表型与标记关联，14个性状共检测到139个显著关联的位点，共覆盖96个SSR标记，其中有31个SSR标记控制多个性状，表现出位点或基因的多效性。此外，结合多年多点的表型数据，在MAGIC群体中筛选获得了18份优良的品系，其中优质棉材料3份、高产棉7份、高衣分材料5份、早熟性材料3份。本研究利用构建的MAGIC群体，较全面解析了陆地棉的遗传基础，检测获得了可用于辅助选择的分子标记以及优良的品系，为陆地棉遗传和育种研究奠定了基础。