基于主-多基因混合遗传模型与遗传图谱解析紫花苜蓿早熟QTL及其与产量性状的关系

Early flowering is an essential trait as it greatly determines biomass yield and quality of alfalfa (Medicago sativa L.). Alfalfa breeding for early flowering cultivar contributes to the farming system regulation, and reducing the loss caused by the meeting of harvesting time and rainy season. It is often supposed that early flowering can limit the potential of yield increase. But there were also recent evidences that some earlier flowering germplasm were with taller height and higher yield. The genetic character and genes regulation mechanism of early flowering traits in alfalfa have not been studied until now. Our research group has bred the early flowering germplasm after years of alfalfa breeding research. And we also constructed the genetic segregation group of earlier flowering which was made with the parents of early flowering and high yield germplasm. It has initially been confirmed that there were great variation in this group and some individuals showed both early flowering and high yield. So we inferred that the target locus for early flowering probably posses the pleiotropic effects. This study is designed to identify the QTL of early flowering traits in alfalfa using mixed major gene plus poly-genes model and linkage mapping. Both methods verifiy each other for testing the major QTL efficiently and accurately. Their pleiotropic effects will be analyzed using the biomass yield data in order to identify the major QTL which accelerate the flowering process but have no negative effects on biomass yield. The prospective results will shed light on genetic characters and molecular mechanisms for early flowering traits of alfalfa. And it can be of practical interest in methods search of improving the trade-off between early flowering and yield, and provides the theoretical guide for genetic improvement of new alfalfa cultivars.

紫花苜蓿的早熟性状与产量、质量等密切相关，培育早熟品种有利于调整耕作制度，减少因雨季与收获期相遇造成的重大损失。通常认为，早开花可能会限制产量的增加，但最近研究发现，部分早熟苜蓿材料的株高与产量较高。关于苜蓿早熟性状的遗传特性和基因作用机理研究迄今国内外尚无报道。本课题组在多年的遗传育种研究中利用典型的早熟原始种质与高产种质杂交，构建了F1代早熟性状分离群体。初步研究表明，该群体存在大量遗传变异，部分单株不仅早熟而且高产，控制早熟的基因位点很可能具有多向性效应。本项目拟在此基础上，综合运用主-多基因混合遗传模型和遗传图谱，解析早熟QTL的数量及效应，二者相互验证，高效精确的获取早熟主效QTL；结合产量性状分析主效QTL的多向性效应，鉴别出既促进早熟又不影响产量的主效QTL；从而明确苜蓿早熟性状的遗传特性和分子机理，探寻协调早熟与产量关系的遗传改良新方法，为培育早熟高产新品种奠定理论基础。

紫花苜蓿的早熟性状与其产量、质量等密切相关，培育早熟品种有利于调整耕作制度，减免因雨季与收获期相遇造成的重大损失。解析苜蓿早熟性状的遗传特性和基因作用机理是有效利用苜蓿种质特性、培育早熟新品种的关键。本课题组利用典型的早熟材料与高产材料杂交构建了F1代早熟性状分离群体，综合运用主-多基因混合遗传模型和遗传图谱研究早熟性状的遗传特性，分析鉴别主效QTL及其效应，二者相互验证，高效精确的获取早熟QTL,并结合产量性状开展早熟QTL的多向性效应分析。研究结果发现，紫花苜蓿早熟性状不符合正态分布规律而呈现出双峰分布的遗传特性，而干重的正态分布曲线和标准正态分布曲线基本重合，表明产量性状服从正态分布。早熟性状主要受两对主效基因控制同时具有加性作用，主基因遗传率在98%以上。构建了高密度四倍体紫花苜蓿遗传连锁图谱，其中父本连锁图共有599个SNP标记，覆盖图距1571.1cM，平均标记间图距2.6cM。母本连锁图共有680个SNP标记，覆盖图距1407.1cM, 平均图距2.1cM。共定位到25个QTL位点，包括产量QTL位点7个、始花期QTL位点6个。其中，位于第8条染色体上的一个产量QTL位点和一个早熟性QTL位点的遗传距离仅为4.513cM，很可能和同一个基因连锁并且存在多向性效应，分别可解释5.9%产量遗传变异和6.1%花期遗传变异。项目成果已发表研究论文2篇，出版专著1部。培养研究生3名，其中1人已获硕士学位。研究结果进一步揭示了紫花苜蓿早熟性状的遗传特性和分子机理，为培育早熟高产苜蓿新品种提供了新的理论支撑。