Analysis Of Genetic Effects For Traits Related To Cold Tolerance In Winter Rape(Brassica Rapa L.)

In order to understand combining ability and genetic mechanism for traits related to cold resistance and agronomic traits in winter rape(Brassica rapa L.). In this study, six winter rape cultivars with different cold resistance were used as parent materials to make complete diallel cross combinations and analyzed genetic effects of physiologic and biochemical, agronomic traits by the method of GriffingⅠ. Estimated genetic distance between six parents through using SSR molecular marker and analyzed relationship between genetic distance and cold resistance traits or special combining ability of F1. All mentioned above can provide theoretical basis for breeding good varieties. The main results were as follows:1. Under cold resistance condition, measured CAT activity, POD activity, SOD activity, soluble protein content, MDA content, soluble sugar content and over wintering rate of parents and F1, and analyzed genetic mechanism of general combining ability(GC A) for these traits. The results showed that general combining ability was significantly different among the seven traits. General combining ability of these traits on Longyou7 were highest expect the GCA of MDA content, and additive effects were positive. Therefore, Longyou7 was the preferred parent to improve cold resistance in winter rape by evaluating on parents.2. Genetic effects of physiologic and biochemical traits related to cold resistance in winter rape were analyzed by QGAStation software of additive-dominance genetic models. The results showed that over wintering rate, POD activity, SOD activity, SS content, relative electrolytic leakage, Chlorophyll content, transpiration rate and stomatal conductance were mainly controlled by additive effects, and CAT activity, MDA content, SP content and net photosynthetic rate were mainly affected by dominant effects. Narrow heritability and broad heritability surpass 50% on over wintering rate, SOD activity, relative electrolytic leakage and transpiration rate, so these 4 traits should be selected in early generation.3. Analysis of 11 agronomic traits in winter rape, the results showed that plant height, branch height, secondary branch number, length of main florescence, pods number of main florescence, pods number per plant, length per pod and yield per plant were greater influence of additive effects than non-additive effects, and primary branch number, seeds per pod and thousand seed weight were largely controlled by non-additive effects. GY performed quite well on general combining ability(GC A), can be used as an important parent when breeding new cultivar with high yield.4. It had detected 16 pairs of primers equipped with polymorphism among 158 pairs of primers, found 39 alleles mutations, got the range of variation in Shannon index: 0.4506~1.3580 and also calculated the range of variation in genetic similarity coefficients: 0.4634~0.7083. According to the method of UPGMA cluster analysis, we can classified six winter rape materials into 4 categories when GS values is 0.63. The range of genetic distance is 0.2868~0.6921 and the average genetic distance is 0.4559. Genetic distance and MDA content, SP content and net photosynthetic rate of specific combining ability were significant and extremely significant level, and other traits were not significant. Between genetic distance and POD activity, the chlorophyll content of F1 generation were not significant, but significant with F1genaration’s other traits. Therefore, we obtained the conclusion: genetic distance can predict cold resistance traits in F1 generation, but it cannot predict special combining ability.