中国玉米骨干亲本黄早四杂种优势形成的遗传基础解析

【目的】杂种优势利用是实现玉米高产育种的重要途径。解析玉米骨干亲本黄早四杂种优势形成的遗传基础,对指导中国玉米骨干亲本高效利用和高产育种具有重要的理论研究意义与生产利用价值。【方法】以玉米黄改系杂种优势类群的骨干亲本黄早四为共同亲本与11个代表性自交系构建的、包含2 000个重组自交系（recombination inbred line,RIL）的巢式关联分析群体（nested association mapping population,NAM）为试验材料,分别与改良瑞德×黄改系杂优利用模式的代表自交系郑58和昌7-2进行测交,并在全国4个玉米主产区10个试验点开展测交群体的多环境产量及重要农艺性状鉴定。在开展NAM测交群体产量和重要农艺性状相关性分析、各性状在NAM群体及其测交群体之间相关性分析基础上,基于高密度遗传图谱,利用联合逐步回归（Joint stepwise regression）模型进行了NAM及其测交群体QTL定位和产量QTL的复等位遗传分析,并对NAM及其测交群体定位QTL所在区域的遗传重组率进行了比较。【结果】表型分析结果表明,2个测交群体的株高和产量相关性状（主要是行粒数和百粒重）与小区产量均表现出较高的正相关关系。但强优势测交组合（郑58测交群体）的产量表现与NAM群体自身的产量表现相关性较低,表明相对于弱优势测交组合（昌7-2测交群体）,强优势测交组合的产量表现受RIL家系自身的产量影响较小。QTL定位结果表明,与NAM群体相比,利用其测交群体检测到的QTL数目较少,但能解释更高的表型变异。昌7-2和郑58测交群体定位到的QTL中,分别仅有27%和25%的位点与NAM群体定位结果重叠或相邻。主效位点的复等位分析结果表明,对于郑58测交群体（强优势测交组合）,在单穗产量QTL中,68.69%的增产等位变异来自骨干亲本黄早四。但在昌7-2测交群体中（弱优势测交组合）,仅有36.36%的增产等位变异来自黄早四。利用郑58测交群体共鉴定到13个重要的产量相关基因组区段,来自黄早四的等位变异在其中的11个区段表现为增产,这些区段对黄早四杂种优势的形成可能具有重要作用。QTL所在区域的重组率分析结果表明,利用郑58测交群体检测到的QTL所在区域具有较低的遗传重组率,符合杂种优势相关位点更容易分布于低重组区的基因组基本特征。【结论】在强优势测验种郑58遗传背景下,来自黄早四的等位变异对测交组合的产量具有重要遗传贡献,定位到的相关遗传区段与玉米杂种优势形成密切相关。

Genetic Dissection of Heterosis for Huangzaosi,a Foundation Parental Inbred Line of Maize in China

【Objective】The utilization of heterosis is an important approach for high yield breeding in maize. Genetic dissection of heterosis for Huangzaosi (HZS), a foundation parental inbred line of HZS Group, would provide valuable information for its efficient use and high yield maize breeding. 【Method】 A nested association mapping population (NAM), developed from Huangzaosi (HZS) as common parent and 11 diverse inbred lines as other parents and consisting of 2 000 recombinant inbred lines (RILs), were test-crossed with Zheng58 (Z58) and Chang7-2 (CH7), the representative tester in the heterotic pattern of "Improved Reid Group × HZS derived Group" in Chinese maize breeding, respectively. Phenotypic data of two NAM test-cross (NAM-TC) populations were collected at 10 locations across four major corn growing areas of China. Correlations among phenotypic traits and among the NAM and its TC populations, were analyzed. Quantitative trait loci (QTL) mapping of yield and related traits for the NAM and its two TC populations were separately conducted using the model of Joint stepwise regression. Meanwhile, multi-allelic effects of yield related QTL were conducted. Finally, the recombination rates around QTL regions were estimated and compared. 【Result】 Plant height (PH) and yield related traits (mainly refer to kernel number per row, KRPR; kernel weight per hundred, KWPH) simultaneously appeared highly positive correlations with plot yield for both the NAM and its two NAM-TC populations. Compared to the CH7-TC population (with weak heterosis), the lower correlation was observed between the yield performance of the NAM and its Z58-TC population. This meant that the NAM RILs contributed less genetic effects for the yield performance of hybrids in Z58-TC population. A smaller number of QTL were detected for each of the NAM-TC populations. However, the QTL of the NAM-TC populations explained more phenotypic variations than those detected in the NAM per se. Only about 27% of the CH7-TC population QTL and 25% of the Z58-TC population QTL overlapped or neighbored the QTL detected by using the NAM per se. The results of multi-allelic effects of grain yield per ear related QTL showed that HZS contributed about 68.69% of the favorable alleles among those QTL mapped in the Z58-TC population. On the contrary, HZS contributed more adverse alleles among those QTL mapped in the CH7-TC population. A total of 13 yield related genomic regions were identified in the Z58-TC population, whose favorable alleles were mostly contributed by HZS. These genomic regions might play important roles in the formation of yield heterosis of HZS. Moreover, QTL detected in the Z58-TC population tended to locate at the regions with low recombination rate, which was consistent with the feature of heterosis related loci tending to distribute at the genomic regions with low recombination rates. 【Conclusion】 Under the background of Z58, a tester with strong heterosis with HZS, the alleles from HZS greatly contributed to the high yield of hybrids. The QTL detected in the Z58-TC population would tightly associate with the yield heterosis of maize.