【作者】 张立武；

【导师】 杨光圣；

【作者基本信息】 华中农业大学 ， 作物遗传育种， 2010， 博士

【摘要】 每角粒数作为甘蓝型油菜产量重要构成因素之一,一直以来受到遗传育种者的重视。我国已选育出一些代表性品种的每角粒数大多在20粒左右。而在育种实践中,华中农业大学油菜育种研究室发现一份每角粒数多且配合力高的品系Y10（6206A）。目前利用该品系已配制出杂交种“圣光86”、“华皖油5号”和“华油杂15号”等多个国家级和省级双低油菜新品种。这些杂交种在大田生产条件下每角粒数可达到23粒以上。尽管Y106在育种中效果显著但其形成及利用的遗传基础不明。对每角粒数的遗传基础进行剖析可为油菜产量的遗传改良提供理论依据。本研究利用甘蓝型油菜每角粒数多的品系Y106和3份不同来源的每角粒数少的品系（HZ396、HZ165和HZ168）为材料,进行了每角粒数的遗传研究和N19连锁群每角粒数主效QTL的定位等工作。主要结果如下:1.通过品系Y106和HZ396配制杂交组合,分析其F₂群体每角粒数的频率分布规律,发现存在多峰,且偏离正态分布,表明可能存在主基因控制该性状。2.为了验证该结果,以3份每角粒数少的品系（HZ396、HZ165、HZ168）为材料,分别与Y106配制正反交F₁。分析亲本与正反交F₁的每角粒数表现,发现:每角粒数在不同年份能较稳定表达,受环境的影响不大;每角粒数受核基因控制,不存在细胞质效应;每角粒数普遍存在不同程度的杂种优势,大值亲本对小值亲本在杂交后代中以显性的方式表现出来。3.通过“主基因+多基因”的遗传分析,发现每角粒数在不同杂交组合中均符合E-0模型,即2对加性-显性-上位性主基因+加性-显性-上位性多基因模型。2对主基因的加性效应值在不同组合间存在差异,变异范围在1.49与3.71之间。杂交组合HZ396×Y106的2对主基因加性效应值明显大于另外两个组合,说明杂交组合HZ396×Y106更有利于2对主基因加性效应的表达,该组合衍生的分离群体更有利于每角粒数主效QTL的检测。主基因的遗传率较大,不同世代（B1, B2和F₂）变化在39%至84%之间,而多基因的遗传率较小,说明主基因发挥着主要作用。4.通过HZ396和其它两份小值材料（HZ165和HZ168）配制杂交组合,分析F₂群体每角粒数的频率分布,发现HZ396和其它两份小值材料不等位。暗示着在不同杂交组合里,不同位点发挥着主要作用。5.为进一步在QTL水平上研究每角粒数的遗传基础,利用品系HZ396与Y106为亲本构建F₁,对F₁进行小孢子培养,得到140份株系的DH群体。利用该DH群体构建了一张包含349个标记（其中SSR标记有151个,其余为AFLP标记）的遗传连锁图,包含19个连锁群,图谱总长1833.9 cM,标记间平均图距5.1cM。与Piquemal等（2005）及Cheng等（2009）国际上已发表的遗传图谱有较好的一致性。6.该DH群体分别在武汉（2007,2008）与甘肃（2009）进行性状的考察。通过QTL元分析,共检测到13个consensus QTL,每角粒数有3个,即cqSS.N8、cqSS.N13和cqSS.N19,千粒重有4个,角果长有6个。其中,有9个consensus QTL表现为主效QTL。不同性状间QTL被整合成6个unique QTL,它们分布在N7、N8、N13和N19连锁群上,都表现出多效性。这些unique QTL在连锁群上的位置和遗传效应方向,在一定程度上可以反映出每角粒数与角果长正相关而与千粒重负相关的关系。其中,位于N19连锁群上unique QTL表现的尤为典型:每角粒数cqSS.N19和角果长cqSL.N19平均解释的表型变异分别为57.77%和29.14%,增效基因来自于Y106,而千粒重cqSW.N19平均解释的表型变异为37.30%,增效基因来自于HZ396。7. QTL cqSS.N19（或简化为qSS.C9）在不同环境中稳定检测到,故作为靶QTL进行定位。考虑到AFLP标记分析基因型的繁琐,期望将两侧的AFLP标记（EA08MC13-150和SA09MC04-220）转化为SCAR标记,结果只有SA09MC04-220成功转化为SCAR标记SCC9-005。进而为了加密该QTL区间的标记,我们利用已发表的Quantum×No2127-17群体（Chen et al., 2007）和Tapidor×Ningyou 7群体（Qiu et al., 2006） N19连锁群上的SSR引物,分析DH群体,新增2个SSR引物（sS2066和sNRG42）。同时利用已公布的白菜公共数据库中A10连锁群上BAC（Bacterial Artificial Chromosomes）末端序列设计SSR引物,新增1个SSR引物SRC9-022。8.采用连续回交的方法,构建了以HZ396为遗传背景的cqSS.N19的近等基因系BC3F₂。区间作图法分析发现,QTL cqSS.N19位于显性的SSR标记SRC9-022和共显性的SCAR标记SCC9-005之间,峰值处为0.60 cM。在BC3F₂群体中,每角粒数解释85.8%的表型变异,加性和显性效应值分别为6.1和5.7粒。这表明,cqSS.N19是Y106在育种中每角粒数效果显著最主要的遗传位点。本研究提出了下面几个进一步研究课题:1.每角粒数主效QTL cqSS.N19的精细定位与克隆,在此基础上,利用重组单株克隆cqSW.N19;2.每角粒数及千粒重和角果长在QTL水平上的相关性进一步深化与拓展,尤其角果籽粒密度（Packing of seed within the silique）;3.每角粒数QTL的聚合效应分析。更多还原

【Abstract】 Seeds per silique （SS） is one of the three important components of yield in oilseed rape （Brassica napus L.） and has always received much attention. By comparing SS in the representive cultivars registered officially in China, it could be inferred that SS was about 20. In the breeding practice, one stable high-SS and high combining ability line‘Y106’（or 206A）, was found by Rapeseed Laboratory of Huazhong Agricultural University. This elite line had been applied to produce many hybrid cultivars, i.e.‘Shengguang 86’,‘Huawanyou No. 5’,‘Huayouza No.15’and so on, registered officially in nation or province trials. And the SS of these hybrids was above 23 in the farmers’fields. Although‘Y106’had remarkable high-SS effect in the breeding programs, the genetic basis of SS remains elusive. Hence, genetic dissection of SS will facilitate formulating breeding strategies for seed yield improvement.The Brassica napus lines,‘Y106’exhibiting high-SS and‘HZ396’,‘HZ165’and‘HZ168’with low to moderate SS, had different genetic backgrounds and were used as parents. We analyzed the genetic studies of SS and mapped the major QTL cqSS.N19 in a B3F₂ population. The main results were as follows.1. The genetic control of SS was primarily studied in the cross of‘HZ396’בY106’. The frequency distribution of the F₂ generation deviated from a normal distribution and appeared to have a multi-modal pattern, indicating the influence of major genes mixed with polygenes.2. To test this hypothesis and uncover the genetic basis of SS in diverse genotypes, three low to moderate SS materials,‘HZ396’,‘HZ165’and‘HZ168’, were selected. An experiment with the orthogonal and reciprocal F₁ generations derived from three crosses,‘HZ396’בY106’,‘HZ165’בY106’and‘HZ168’בY106’, along with their parents was conducted for investigating the heterosis and cytoplasmic effects of this trait. Results revealed that SS more or less unaffected by environments, that SS was controlled by nuclear genes instead of cytoplasmic genes, that there were all levels of dominance from partial to full dominance in the F₁ as the major contributor to heterosis and the higher-SS genotype was almost completely dominant over the lower-SS genotype.3. The major genes and polygenes mixed genetic model was used to analyze SS in rapeseed. The joint segregation analysis revealed that SS was best described by the E-0 genetic model, a case of two additive-dominace-epistasis major genes as well as additive-dominace-epistasis polygenes. The additive effects of the two major genes ranged from 1.49 to 3.71 in the three crosses. And the additive effects of two major genes in the cross of‘HZ396’בY106’were obviously larger than those in the other two crosses, which demonstrated that the two major genes for SS in the cross of‘HZ396’בY106’could easily be detected and passed on to offspring. Significant progress could be made in mapping the two major genes contributing to SS by constructing mapping populations using‘HZ396’and‘Y106’as parental lines. Heritability of the major genes varied from 39% to 84% in diverse generations （B1, B2 and F₂）, which was much larger than that of the polygenes. It meant that SS was mainly controlled by major genes.4. Allelic tests of the three low to moderate SS materials,‘HZ396’,‘HZ165’and‘HZ168’were performed by the frequency distribution of the F₂ generations. Results revealed that the three lines were probably non-allelic, which meant that the major genes varied according to the specific crosses performed.5. To dissect the genetic basis of SS, we used one F1 plant of the cross of‘HZ396’בY106’to develop double haploid （DH） population. The DH population, consisted of 140 lines, was used for map construction and QTL analysis. A linkage map comprising 151 Simple Sequence Repeat （SSR） and 198 Amplified Fragment Length Polymorphism （AFLP） markers covering 1833.9 cM with an average interval of 5.1 cM between adjacent markers was constructed. The order of most markers is consistent with the published linkage maps of Piquemal et al. （2005） and Cheng et al. （2009）.6. In field experiments across three seasons and two locations in China 140 doubled haploid lines and their corresponding parents were evaluated for silique-traits. Quantitative Trait Loci （QTL） meta-analysis revealed that 6, 3 and 4 consensus QTL for silique length （SL）, SS and seed weight （SW） respectively. Of them, 9 QTL showed main effects. And 6 unique QTL were pleiotropic and mapped on linkage groups N7, N8, N13 and N19, which reflected significant correlation of all pairs of the silique-traits by the genomic location and effects of QTL detected. For the unique QTL in the linkage group N19, the additive effects of cqSS.N19, which explained 57.77% of the phenotypic variance of SS, and cqSL.N19 were positive while the additive effect of cqSW.N19 showed a negative effect at the same locus in the linkage group N19, which is a hint for the reason of positive correlation coefficient between SS and SL while negative correlation coefficient between SS and SW.7. Since the major QTL cqSS.N19 （for simplicity, designated as qSS.C9） was stable across various environments, we selected this QTL as a target QTL to map. Given that AFLP has limitations in genotype analysis, we attempted to convert the two AFLP markers EA08MC13-150 and SA09MC04-220 into SCAR markers. And only SA09MC04-220 successfully converted into codominant SCAR marker SCC9-005. To enrich the markers located in the target QTL further, we utilized the SSR markers in the published linkage maps of Chen et al. （2007） and Qiu et al. （2006） and developed SSR markers from the end sequence of BAC in the linkage group A10 in Brassic rapa. Results revealed that 3 SSR markers （sS2066, sNRG42 and SRC9-022） were enriched in the linkage group N19.8. For the consensus QTL, cqSS.N19, we constructed one near isogenic-line （BC3F2） in the HZ396 background by consecutive backcrossing, according to the primary QTL identified in DH lines. QTL analysis based on the BC3F2 population showed that this locus was located between the dominant SSR marker SRC9-022 and co-dominant SCAR marker SCC9-005. The QTL peak was near SRC9-022 marker at a distance of 0.60 cM. Furthermore this locus explained 85.8% of phenotypic variance with additive and dominant effects of 6.1 and 5.7 SS, respectively. The finding suggested that the locus was major for SS of‘Y106’, which had remarkable high-SS effect in the breeding programs.Three aspects of research work in the future are as follows: 1. Fine mapping and cloning of major QTL cqSS.N19; 2. Cloning of cqSW.N19 using recombinants based on cloning of cqSS.N19; 3. Expanding and deepening the correlation of all pairs of the silique-traits at the QTL level, especially packing of seed within the silique; 4. Genetic analysis of pyramiding QTL of SS.更多还原