中国玉米地方品种种族的遗传变异评估

Assessment of Genetic Variation in Different Races of Maize Landraces in China

【目的】通过DNA水平的分子评价,明确中国玉米9个种族的遗传变异,并揭示各种族之间的遗传关系与群体分化特性,为中国玉米种族的形成与演变等相关研究奠定基础,同时也为种族资源的高效利用提供参考。【方法】利用覆盖玉米全基因组的55个SSR标记,对基于中国库存玉米所划分的9个玉米种族的224份代表性材料进行分子鉴定。获得所有标记的片段长度数据后,利用Power Marker软件(V3.25)中的Summary模块计算224份材料的平均等位变异、基因多样性与多态性信息含量(polymorphism information content,PIC),并通过重取样策略,利用Wilcoxon秩和测验分析了9个种族在相同样本容量水平上3个遗传多样性参数的差异水平。利用Power Marker软件中的Phylogeny模块计算了9个种族的欧氏距离,并以此进行种族的聚类分析;利用该软件中的Structure模块对9个种族进行分子变异分析(analysis of molecular variance,AMOVA),并计算各种族的群体分化系数(FST),以此进行各种族群体分化检测。【结果】55个SSR所检测到的中国9个玉米种族的等位变异、基因多样性与PIC等3个多样性参数的幅度分别为4.42—7.64个/位点、0.5788—0.6532与0.5334—0.6117,平均值依次为11.53个/位点、0.6315与0.5953。西南黄色硬粒种族与衍生种族的平均等位变异相对较高,但基于重取样的分析结果表明这9个种族在这3个多样性参数上的差异均不显著(P>0.05)。聚类结果显示,9个种族分成了3个类群,其中爆裂种族形成1个独立类群,3个北方种族形成1个类群,剩下的5个种族(3个西南种族、1个糯质种族、1个衍生种族)形成1个类群。AMOVA分析结果表明,9个种族之间的分子变异程度约为3%,远小于这些种族内部所检测到的分子变异(50%)。9个种族的群体分化系数(FST)为0.29%—7.63%,其中,西南白色硬粒种族与南方糯质种族、西南马齿种族与西南黄色硬粒种族、西南马齿种族与衍生种族之间的FST均相对较小,分别为0.29%、0.70%与0.80%,说明其遗传关系更近。【结论】在长期的人工选择与自然选择过程中,中国玉米9个种族蕴藏丰富的遗传变异。西南白色硬粒种族与糯质种族之间的分化程度远低于其他种族,前者在糯玉米资源的起源进化中可能扮演重要角色;西南黄色硬粒种族和西南马齿种族与衍生种族之间的分化程度很低,表明这2个种族对衍生种族的形成可能有重要作用。

【Objective】Genetic variation of nine races of maize landrace germplasm in China was revealed via DNA markers.Genetic relationships and population differentiation of these races were also discussed. All the results will provide informative reference for the following researches focused on uncovering formation and evolution of races, and efficient utilization of different races.【Method】In the present study, 55 SSRs covering the whole maize genome were used to assess the genetic diversity of 224 landraces that represent the nine maize races classified previously based on the germplasm preserved in China National Gen Bank. Three diversity parameters, including the average alleles per locus, gene diversity, and polymorphism information content（PIC）, of all these 224 landraces were calculated by the Summary Manu of Power Marker V3.25. Statistical differences among these diversity parameters of the nine races were determined via Wilcoxon signed-rank test at the same sample size level through resampling strategy. Euclidean distances of these nine races were calculated by the Phylogeny Manu of Power Marker, and the clustering analysis based on the Euclidean distance was carried out among these races. Analysis of molecular variance（AMOVA） of these nine races was carried out by the Structure Manu, and the FST between the race pairs of these nine races was also estimated. 【Result】The diversity results revealed by 55 SSRs showed that the average alleles per locus, gene diversity and PIC were 11.53, 0.6315, and 0.5953, respectively, ranging from 4.42 to 7.64, 0.5788 to 0.6532, and 0.5334 to 0.6117, correspondingly. Though the two races of Southwestern Yellow Flints and Derived Race possessed relatively higher number of alleles per locus, no statistical differences of these three genetic diversity parameters were detected by the resampling strategy within each pair of races（P〉0.05）. Nine races were assigned into three clusters, and one cluster was consisted of popcorn race, another cluster was consisted of 3 northern races, and the rest five races including Waxy Race, Derived Race and three southwestern races formed the third cluster. Results from the AMOVA indicated that the molecular variance among races was only 3%, far less than that detected among accessions within races（50%）. FST of the race pairs ranged from 0.29% to 7.63%, and the FST of Southwestern White Flints vs Southern Waxy Race（0.29%）, Southwestern Yellow Flints vs Derived Race（0.80%）, and Southwestern Dents vs Derived Race（0.70%） were relatively lower than those of the other race pairs.【Conclusion】A total of 634 alleles were detected by 55 SSRs covered the entire maize genome within the nine races, suggesting that abundant genetic variation exists within the germplasm of these nine maize races formed during the long-term artificial and natural selection in China. In addition, the close relationships and relatively lower FST of the races or race pairs suggested that Southwestern White Flints might act as the fundamental germplasm base of Southern Waxy Race（FST=0.29%）. The lowest FST of Derived Race vs. the other eight races were observed between the race pairs of Derived Race vs Southwestern Yellow Flints（0.80%） and Derived Race vs Southwestern Dents（0.70%）, implying that these two races might play more important roles in the formation and evolution of Derived Race.