不结球白菜（Brassica campestris ssp. chinensis Makino）是十字花科芸薹属中最重要的蔬菜作物之一，原产中国，不仅营养丰富而且具有适应性广及生长迅速等特点，在中国、韩国、日本等东亚国家普遍栽培，近年来欧美等国家也广泛引种逐渐成为世界性的重要蔬菜。其许多重要农艺性状都是由数量性状位点控制，这些数量性状具有较复杂的遗传机制。而遗传连锁图谱的构建和重要农艺性状QTL定位可以为揭示这些复杂机制奠定良好基础。本研究利用双单倍体群体构建了不结球白菜遗传连锁图谱，并在此基础上进行了主要农艺性状的QTL定位研究。研究结果如下： 1．利用DH群体构建不结球白菜遗传图谱 为了将不结球白菜分子遗传图谱和国际上A基因组参考图谱对应起来, 利用国际上发表的大白菜和甘蓝型油菜A基因组特异SSR标记作为锚定标记, 以164个DH株系组成的群体为作图群体进行了分子遗传图谱的构建研究。共筛选到231个在双亲间具有多态性的标记并用于图谱构建，在此基础上构建到一张由10条连锁群组成的图谱，其长度分布在39.44 cM 和126.66 cM之间，共包含了99个SSR标记和47个SRAP标记。图谱全长为678.25 cM，每个连锁群上的标记数目为5-50个，其中A02连锁群上标记数最多为50个，A10连锁群上标记最少只有5个。图上标记间平均距离为4.65 cM，标记间距离为2.53 cM-10.98 cM。A02连锁群上标记密度最大，A07连锁群标记间距离最大为10.98 cM。在A02和A05连锁群上各有一个大于20 cM的空隙。根据芸薹属A基因组遗传连锁群上定位的SSR标记，将各连锁群按A参考图谱的连锁群进行命名, 即A01 – A10, 并与10条染色体对应起来。在本研究结果的基础上可继续增加分子标记数目，最终有利于开发不结球白菜中与重要农艺性状紧密连锁的分子标记，进而为分子标记辅助选择奠定良好基础。 2．光合色素含量的QTL定位与分析 对复杂农艺性状进行QTL定位及分子标记辅助育种是现代育种中非常重要的环节。为揭示出控制光合色素含量的QTL位点并寻找与QTL位点紧密连锁的分子标记，我们利用包含有112个株系的不结球白菜DH群体进行了光合色素含量QTL定位与分析。该群体通过对两个高代自交系材料SW-13和SU-124杂交所得的F1后代‘暑绿’进行游离小孢子培养获得。在‘暑绿’图谱基础上进行增加标记和整合，通过在芸薹属A基因组参照图谱中公共的SSR标记将连锁群与染色体相对应。采用复合区间作图法（CIM）对叶片叶绿素a、叶绿素b、总叶绿素、类胡萝卜素含量、叶绿素a/b进行了QTL 定位和遗传效应分析。共检测到11个QTL位点，分布在3条连锁群上，分别是A02, A08和A10。其中可解释变异率最大值达38.0%。研究结果以期为不结球白菜高光效增产育种分子标记辅助选择提供理论依据并为芸薹属其他作物的相关育种程序提供参考价值。 3．抽薹开花性状的QTL定位与分析 春季生产中，不结球白菜先期抽薹直接导致其产量和商品质量下降。因此选育耐抽薹的品种是实现不结球白菜周年供应的重要途径之一。本研究利用已构建的包括164个株系的DH群体和两年的重复试验结果，采用复合区间作图法对不结球白菜与抽薹开花天数等相关的QTL进行定位及遗传效应的分析。在10个连锁群上共检测到19个QTL，主要分布在A02、A04和A05连锁群上：控制现蕾天数的QTL有5个，控制抽薹天数的QTL有6个，控制开花天数的QTL有6个，控制抽薹指数的QTL有2个；另外估算了单个QTL的遗传贡献率和加性效应，发现各QTL加性效应各不相等，各位点的遗传贡献率介于10.26%-21.19%之间；相关性状QTL的位置往往集中在连锁群上相同或相近的区域。这些定位到的QTL将为不结球白菜抽薹开花时间等性状的分子标记辅助选择提供理论基础。 4．与产量相关的QTL定位与分析 应用SSR和SRAP分子标记构建的146个标记位点的不结球白菜遗传连锁图谱和164个DH株系群体，采用Win QTL Cartographer 2.5软件的复合区间作图法对不结球白菜与产量性状相关的QTL进行定位及遗传效应的分析。在10个连锁群上共检测到26个QTL，主要分布在A02、A05和A07连锁群上：控制叶片叶柄重量比值的有4个，控制叶柄厚度的有5个，控制叶片重量的有3个，控制叶柄重量的有2个，控制单株重的有2个；另外估算了单个QTL的遗传贡献率和加性效应，发现各QTL加性效应各不相等，各位点的遗传贡献率介于5.28%-22.26%之间；一些控制不同性状的QTL位点在连锁群上共连锁。这些定位到的QTL将为不结球白菜产量等性状的分子标记辅助选择提供理论基础。

Non-heading Chinese cabbage (Brassica campestris syn. rapa ssp. chinensis Makino) is one of the most important vegetable crops in the Brassica genus. Non-heading Chinese cabbage, known as Pak Choi, originated in China, is among the most popular vegetables crops in eastern Asia like China, Korea and Japan and is now common in Europe and America. Like the other Brassicas, non-heading Chinese cabbage is a good source of nutrients and has the characteristics of extensive adaptability and fast growth. Many important agronomic traits are quantitative in nature and have a complex genetic basis. The identification of quantitative trait loci (QTL) represents a first step towards dissecting the molecular basis of such complex traits. A pre-requisite for QTL mapping studies is the availability of genetic maps. Its molecular marker-based linkage map construction and QTL mapping will provide an available reference to genomic structural study and genetic breeding in non-heading Chinese cabbage. In this study, several doubled haploid (DH) populations of non-heading Chinese cabbage were obtained through isolated microspore culture, and then used for molecular genetic linkage map construction, and mapping QTL for several important agronomic traits. The results are as follows: 1．Construction of a Genetic Linkage Map Using DH Population in Non-heading Chinese Cabbage In this chapter, a DH population including 164 lines was used to construct a detailed genetic map to establish the identity of linkage groups corresponding to reference map of Brassica A genome. A set of simple sequence repeats (SSR) markers provided anchors to previously published linkage maps for B. campestris and B. napus, and was used to designate linkage groups. Our selection of primer pairs corresponded to 231 genetic loci that we were able to map. The resulting consensus map presented 10 linkage groups ranging from 39.44 to 126.66 cM, including 99 SSR markers, 47 sequence-related amplified polymorphism (SRAP) markers. The total length of the map was 678.25 cM and the average interval distance of the linkage map was 4.65 cM. The number of markers on the 10 linkage groups ranged from 5 (A10) to 50 (A02), with an average interval distance from 2.53 cM (A02) to 10.98 cM (A07). A map interval with the markers separated more than 20 cM was observed on A02 and A05, respectively. Accordingly, these linkage groups were named following the A01 to A10 of reference map, and were assigned to corresponding chromosomes. This map could be used to identify more markers, which would eventually be linked to genes controlling important agronomic characters in non-heading Chinese cabbage. Furthermore, considering the good genome coverage we obtained, together with an observed homogenous distribution of the loci across the genome, this map is a powerful tool to be used in marker assisted breeding. 2．Quantitative Trait Loci for Photosynthetic Pigment Concentration Quantitative trait loci (QTL) mapping and marker development are essential steps in any molecular breeding programme. In this study, QTL for photosynthetic pigment concentration were identified using a DH population of 112 lines derived from an F1 hybrid of non-heading Chinese cabbage, ‘Shulv’, obtained from a cross between Brassica campestris lines SW-13 and SU-124 through microspore culture. QTL mapping was carried out using a modification to the map of ‘Shulv’. Alignment of the linkage groups was carried out with those of reference B. campestris maps, allowing the assignment of these groups as A01 – A10. QTLs underlying photosynthetic pigment concentration in leaf were mapped with composite interval mapping (CIM) method, the numbers, location, explained variation and additive effect of QTLs were determined. In total, 11 QTL were associated with photosynthetic pigment concentration and identified on linkage groups A02, A08, and A10.The maximum phenotypic variance for a single QTL was 38.0%. Markers closely linked to these QTL could assist in the development of non-heading Chinese cabbage cultivars with increased yield, due to having improved photosynthetic capabilities. The objectives in this study were to investigate QTL underlying photosynthetic pigments concentration and to facilitate breeding for high photosynthetic efficiency through marker assisted selection (MAS) in non-heading Chinese cabbage and, through homology based approaches other Brassica crops. 3．Mapping QTL for Bolting and Flowering Time Traits Early bolting of non-heading Chinese cabbage during spring cultivation often has detrimental effects on the yield and quality of the harvested products. Breeding late bolting or flowering is a major objective to enable year-round production for the non-heading Chinese cabbage. With CIM method, a genetic linkage map of non-heading Chinese cabbage were adopted to map and analyse QTL controlling the days of bolting and flowering. This study was based on a DH population with 164 lines in two years. The results as follows: 19 putative QTLs, including 5 for days of squaring, 6 for days of bolting, 6 for days of flowering, 2 for bolting index were major mapped on A02, A04 and A05 linkage groups. There were unequal gene effects on the traits and unequal variation explained on the expression of the bolting and flowering time traits. These QTLs individually explained between 10.26% and 21.19% of the phenotypic variation. The QTL of associated traits often located on the same loci or near region of a linkage group. These mapped QTL could be used to marker assisted selection program for the bolting and flowering time traits in non-heading Chinese cabbage in the future. 4．Mapping and Analysis of QTL Controlling Yield Components A SSR and SRAP genetic linkage map with 146 markers and a DH population with 164 lines were employed in mapping and analysis quantitative trait loci. The number, location, variation explained and additive effect of QTL underlying yield trait were determined by using CIM method with software Win QTL Cartographer 2.5. The results as follows: 26 putative QTLs, including 4 for ratio of blade and petiole, 5 for petiole thickness, 3 for blade weight, 2 for petiole weight, 2 for plant weight were major mapped on A02, A05 and A07 linkage groups. There were unequal gene effects on the traits and unequal variation explained on the expression of the yield trait. These QTLs individually explained between 5.28% and 22.26% of the phenotypic variation. Co-location of QTL for different traits was found in many cases, which might suggest pleiotropy or tight linkage. These mapped QTL could be used to marker assisted selection programme for the yield trait in non-heading Chinese cabbage in the future.