黄瓜果皮蜡粉量遗传分析及QTL定位

【目的】黄瓜是世界上一种重要的蔬菜，2012年产量已超6.5亿吨。黄瓜果实品质一直备受育种者关注，尤其是果实风味、营养和外观品质。前人对影响黄瓜果实外观品质的相关性状已有深入的研究，但对黄瓜果皮蜡粉量性状长期未得到足够关注。黄瓜果皮蜡粉量作为黄瓜重要的外观品质性状之一，对其进行遗传分析和QTL定位将有助于了解果皮蜡粉形成的分子机制，为黄瓜果皮蜡粉量基因的精细定位及克隆奠定基础，同时也为利用分子标记辅助选育少蜡粉的黄瓜新品种提供理论依据和技术支撑。【方法】利用黄瓜多蜡粉品系‘PI183697’和少蜡粉品系‘1101’构建六家系世代群体，并于海南和北京不同环境条件下种植。在商品瓜成熟时期，采用分光测色计（CM-700d）对六家系世代群体各单株上商品瓜的蜡粉量进行定量测量，每个单株选取2-3个商品瓜，每个商品瓜上选取五处进行测定，然后计算平均数，根据计算结果进行黄瓜蜡粉性状的遗传分析。利用2个亲本对1 288对SSR引物进行筛选，从中挑选出128对多态性较好的标记，对F₂群体进行分析，取最小阈值LOD3.0采用JoinMap4.0软件进行遗传图谱构建。利用MapQTL4.0软件，结合构建的遗传图谱进行果皮蜡粉量QTL定位。【结果】在黄瓜野生品系‘PI183697’中，黄瓜果皮蜡粉量的遗传符合数量性状的特征，采用植物数量性状主基因+多基因混合遗传模型对六家系世代的黄瓜果皮蜡粉量进行分析，得出黄瓜果实果皮蜡粉量的遗传符合1对加性主基因+加性-显性多基因（D-2）模型。利用2个F₂群体分别构建了两张包含7条染色体、128对SSR标记的遗传图谱。2次共检测到7个与蜡粉量相关的QTL位点，在第1、3、5染色体上各检测到1个位点，分别为WP1.1、WP3.1和WP5.1，在第6染色体上检测到4个位点，分别为WP6.1、WP6.2、WP6.3和WP6.4，其中WP5.1和WP6.2 2个QTL位点在两季中均被检测到，LOD值分别为7.70、4.81和4.21、6.69，贡献率分别为14.9%、12.4%和8.0%、16.7%。 【结论】黄瓜果皮蜡粉量的遗传符合数量性状特征，由1对加性主基因+加性-显性多基因控制（D-2）。第5染色体上的WP5.1和第6染色体上的WP6.2均可重复检测到，因此，推断控制蜡粉含量的主效候选位点可能位于第5或第6染色体上。

Genetic Analysis and QTL Mapping of Wax Powder on the Surface of Cucumber Fruit

【Objective】Cucumber (Cucumis sativus L.) is an important world vegetable in the world and its output was over65 000 million kilos in 2012. For many years, plant breeders have focused their attentions on improving fruit quality, especially in flavor, nutrition, and appearance of cucumber. Several researches on the traits to affecting the appearance quality of cucumber fruit have been reported. However, up to now the amount of wax on the surface of the fruit has received little attention. Wax powder is one of the important fruit appearance quality traits in cucumber. The inheritance and QTL mapping will help to understand the molecular mechanism of wax powder formation, lay a foundation for the fine mapping and gene cloning, and provide a theoretical basis for selecting cucumber lines with little wax powder.【Method】In this study, six generations were developed from the cross between cucumber lines with heavy wax powder ‘PI183697’ and light wax powder ‘1101’ under different environmental conditions of Hainan and Beijing. The amount of wax powder on the fruit surface was measured quantitatively with colour meter (CM-700 d).2-3 cucumbers in each individual and five parts on each cucumber were selected for measurement, and then the calculated average values were used to estimate the inheritance. For the genetic analysis, 1 288 SSR markers were tested and 128 that were found to be polymorphic between ‘PI183697’ and ‘1101’ were used for linkage analysis of F₂ populations. A linkage group was constructed by using JoinMap4.0 with minimum LOD 3.0, and QTL detection for wax powder was conducted with MapQTL4.0.【Result】Genetic analysis showed that the trait of wax powder in ‘PI183697’ was inherited quantitatively. The mixed major gene plus polygene inheritance model of plant quantitative traits was applied to the six generations for genetic analysis. The result showed that the trait of wax powder on cucumber fruit surface was controlled by one additive major gene plus additive-dominant polygene (D-2 model) in the joint analysis of six generations. Linkage maps from two F₂ populations containing seven chromosomes and 128 SSR markers were constructed and seven QTLs relating to wax powder were identified. One QTL locus on Chr.1, Chr.3 and Chr.5, respectively, and four loci on Chr.6 were detected, which were WP1.1, WP3.1, WP5.1, WP6.1, WP6.2, WP6.3 and WP6.4. The QTL loci WP5.1 and WP6.2 were detected in two seasons, having LOD scores of 7.70, 4.81, 4.21, and 6.69, and R² of 14.9%, 12.4%, 8.0% and 16.7%, respectively. 【Conclusion】The inheritance of wax powder is quantitative and controlled by one additive major gene plus additive-dominant polygene (D-2 model). According to QTL mapping, the QTL loci WP5.1 and WP6.2 were repeatedly detected. Thus it was predicted that the major QTL loci may be located on Chr.5 and Chr.6.