Genetic Effects Analysis And QTL Mapping Of Major Plant-type Traits In Brassica Napus L.

Oilseed rape is one of the most important oil crops in China. The increased crop yields as well as mechanized production have been the primary task in breeding and cultivations. The completion of this task requires theoretical basis which could be provided by thorough research in genetics and QTL mapping of plant-type traits. In this study, F2hybrids from combination of the loose-type S33B and the compact-type86-5-10-17Brassica napus were used as target population, in which we discussed the growth dynamic and genetic rule of four traits that strongly associated with mechanized harvest---plant height, branch height, branch count and branch angle. Furthermore, QTL mapping was accomplished after linkage map construction. Our results were as follows:1. According to the branch angle, Brassica napus L. could be divided into three categories:compact-type, medium-type and loose-type. These three types have different growth dynamics in plant height, branch height and branch count. However, same tendencies for growth were observed. Oilseed rapes grew rapidly from initial-bloom stage to full-bloom stage in aspects of plant height, branch height and branch count. Growth speed of plant height and branch count ranking from higher to lower was:medium-type> loose-type> compact-type while one for branch height was:loose-type> medium-type> compact-type.2. In compact-type plants, the1st and3rd branch angle symbolized as a slow decrease-increase-rapid decrease model; the2nd branch angle symbolized as an increase-decrease model; the4th branch angle symbolized as a constant decrease model throughout the growing season. In medium-type plant, the tendency of2nd and4th branch angle is identical which symbolized as decrease-increase model; the1st branch angle symbolized as a decrease-increase-decrease model; the3rd branch angle symbolized as a constant increase model. In loose-type, the symbolized models for1st,2nd,3rd and4th branch angle were constant increase, decrease-increase, slow decrease-increase and decrease-increase respectively. 3. The height and branch count of F1population had higher orthogonal&reciprocal phenotypic values than its F0population, which indicated these two traits in F1had remarkable heterosis; The branch angle of F1population had phenotypic value between ones of the Fo population and was much closer to the value of parental S33B, which indicated the existence of major additive effect and partial dominant effect (loose-type to compact-type) in branch angle-control genes. The branch height of F1population had higher orthogonal phenotypic values than its Fo population while its reciprocal phenotypic value between the Fo population’s and much closer to the value of parental86-5-10-17, indicated the probably existence of cytoplasmic effect.4. Plant height of Brassica napus was in correspondence with two pairs of major genes model (B-6model) and these two genes had identical additive effects and dominant effects respectively with no epistasic effect. Branch height was in correspondence with additive effect and partial dominant/overdominance effect model (A-1model) of one pair of major genes. Branch count was in correspondence with identical addictive effect model of two pairs of major genes (B-4model) with no dominant effect and epistasic effect. Branch angle average was best described by additive-dominance-epistasis inheritance model (B-1model). The major gene heritability of four traits (Plant height, branch height, branch count and branch angle) which controlled by two major genes were44.71%,4.43%,4.55%and60.52%respectively. While the corresponding polygenes heritability were1.36%,8.34%,0.56%,0.95%), much lower than their major gene heritability.5. Having selected223pairs SSR markers to construct a genetic linkage map of F2population which contained13linkage groups of163effective markers, while60marker locus which accounted for26.9%of the total number did not appeared in any linkage group. The genetic distance and the average distance were906.986cM and12.286cM respectively and range for maker number within groups was2to63. Genetic distances of three groups:LG1, LG2and LG8exceeded100cM. LG1being the longest---177.222cM, while LG13as the shortest---9.481cM. The range of average distance was between LG11and LG1,30.968cM and2.858cM separately.6. Eleven QTLs with comparatively larger heritability were detected with LOD score greater than2.0in plant-type traits of F2populations, locating in linkage group LG1, LG2, LG3, LG5and LG8. Among them, four QTLs of plant height which located in linkage group LG1and LG2, accounting for8.54%to17.04%of the phenotype variation; Five QTLs of branch height which located in LG3, LG5and LG8, accounting for3.92%to21.82%of the phenotype variation; One QTL of branch number in LG3, accounting for11.08%of the phenotype variation while another QTL of branch angle in LG1accounts for14.16%of the variation. Only one QTL in branch height sourced, branch number and branch angle’s QTL from loose-type parental S33B totally, while others came from compact-type parental86-5-10-17. The QTL mapping of plant type laid solid foundation for further fine mapping and marker-assist breeding as well as function study by gene clone.