Studies On Heredity And Heterosis Of Plant-type Traits In Compact Rapeseed Lines

In this study, 36 crosses were made by Griffing methodⅠwith 6 compact and loose rapeseed lines of Brassica napus L. which have different genetic background. Analysis of variance, genetic effects, correlation analysis and heterosis analysis were firstly made on 17 plant-type traits by ADM model and MINQUE(1); Genetic decision analysis was also performed on aim yield traits and plant-type traits by decision-coefficient. The main results were obtained: 1 The estimated proportion between components of genetic variance and phenotypic variance indicated that plant height, effective branch height, pods of primary branches, pods of main raceme, pods per plant, seeds per pod, 1000-seed weight, length of pod, angle between stem and primary branch were controlled with both additive and dominant effect, and dominant effect is stronger than additive effect for plant height, on the contrary, additive effect is stronger than dominant effect for other characters. Length of main raceme, No.of primary branches, width of pod and length of primary branch were mainly controlled by additive effect. Pods per plant, seeds per pod, 1000-seed weigth and length of pod were controlled not only by additive effect and dominant effect, but also affected by female parent. 2 The analysis of dominant trend of plant-type traits showed that dominant genes have reduced-action for angle of between stem and primary branch,but have synergism for plant height, effective branch height, pods per plant, branch–end height,seed per pod,1000-seed weight and length of pod. 3 Genetic correlation analysis showed that length of main raceme, pods of primary branches, pods of main raceme, pods per plant, relative length of primary branch and length of primary branch were significantly positive additive correlated with yield per plant; but effective branch height, branch-end height, No.of primary branches, 1000-seed weight and length of pod were significantly negative additive correlated with yield of per plant; however, plant height, relative length of branch in stem, density of pod and angle between stem and primary branch were no significantly additive correlated with yield per plant . 4 Path analysis indicated that pods per plant had great directly and totally effects for yield per plant, 1000-seed weight and seeds per pod had great directly effect on yield per plant, however they have also great indirectly negative effect through other traits on yield per plant, as a result, they have not great total effect on yield per plant. Directed effect of plant-type traits on yield per plant are not great, but some of them such as effective branch height, length of main raceme, pods of primary branch, pods of main raceme, width of pod and length of primary branch have great indirectly effect on yield per plant. 5 Genetic decision analysis showed that pods per plant and pods of primary branch are principal decisive traits and No.of primary branch, length of main raceme, width of pod, density of pod, length of pod, branch-end height, angle between stem and primary branch and plant height are secondary decisive traits for yield per plant. 1000-seed weight, effective branch height, pods of main raceme, seeds per pod are principal restricted traits and relative length of primary branch, length of primary branch and relative length of branch in stem are secondary restricted traits . 6 Heterosis analysises showed that heterosis of yield per plant is the best, its mid-parent heterosis and better-parent heterosis in F1 generation are 35.1% and 29.5% respectively, and its mid-parent heterosis and better-parent heterosis in F2 generation are 17.6% and 12.0%. In components of yield per plant, the mid-heterosis for pods per plant is very weak (1.4%), Heterosis of 1000-seed weight and seeds per pod in F1 generation are 6.5% and 5.3% respectively. Significant positive mid-heterosis in F1 generation for effective branch height, plant height, length of main raceme, pods of main raceme, length of pod and width of pod were observed. At the same time, significant negative mid-parent heterosis and better parent heterosis for angle between stem and primary branch were also observed, which suggested that it need only one compact parent for compact F1 cross. This study has important theory significance in breeding compact rapeseed variety and using parents.