Study On Genetic Diversity And Heterosis Of Novel Prematured Spring Rapeseed (Brassica Napus L.)

Heterosis as a common biological phenomenon in nature is an efficient approach to increase crop yield. The study of genetic diversity is the basis of germplasm evaluation and heterosis application. Thus, understanding the genetic diversity of parental lines and partitioning parents to different genetic groups can help to select for combinations with strong heterosis and elevate the efficiency of heterosis breeding. Different methods have been attempted for heterosis prediction over a long period, however, none of them is sufficient. Along with the development of biotechnology, molecular techniques have been widely used in the prediction of heterosis and the study of genentic basis in many crops. However, there are many opinions about the issue of the correlation between genetic distance and heterosis.This study used 60 prematured spring Brassica napus lines and their three parents. SSR and SRAP markers were used to investigate the genetic diversity and genetic groups of these materials, revealing the genetic difference on molecular level. The materials for heterosis study consisted of 3 spective maintainers of sterility lines (S1,S2,S3), ten restorer lines (R1～R10), 30 F1 hybrids from 10 restorer lines and 3 sterility lines. The correlation between genetic distance and heterosis of various agronomic traits was analyzed based on SSR and SRAP markers. The main results are as following:1. 39 SSR primer pairs generated a total of 145 polymorphic bands, which took 97.3% of total amplified bands. 3.7 polymorphic bands in average. The molecular size was between 50～550bp. 30 SRAP primer pairs generated a total of 252 polymorphic bands, which took 61.9% of total amplified bands. 8.3 polymorphic bands in average. The molecular size was between 150～800bp.2. The result of UPGMA analysis to the data of SSR and SRAP indicated that all tested-cultivars can be classified into two groups as A and B at 0.588 similarity index level. Group A was made up with one of parents-HAOYOU11 (B. campestris L.) and one premature spring-planted variety. Group B was made up with 62 premature spring-planted varieties and two other parents (E144 and 039) of B. napus L. In addition, group B was classified six second types at 0.732 similarity index level. The varieties generated from the same combination were in different second types but not in the same one. It showed that the genetic diversity of spring varieties of B. napus L. created by using the method of interspecific cross between the varieties of B .napus L. and B. campestris L. was quietly rich.3. The result of analysis to the genetic ingredient of prematured spring Brassica napus lines indicated that the ingredient of B. campestris L.was transfered into Brassica napus lines. The ratios of being transferred into the ingredient of B. campestris L. were different along with varieties(1.25%～18.84%). The genetic foundation of rapeseed in existence was widened by being transferred into the ingredient of B. campestris L.4. High parent heterosis (HPH) of yield per plant ranged from -17.72%to 97.21%. Among them, there were 28 combinations whose HPH were more than 50% and 22 combinations whose HPH were more than 20%, the ratio of which were 93.3% and 73.3% respectively.In addition, in the 22 combinations above, 14 combinations were new type of varieties( B. napus L.)×new type of varieties( B. napus L.),7 combinations were new type of varieties( B. napus L.)×nature varieties( B. napus L.), which indicated that strong heterosis can be gained both by using the method of cross between the new type of varietie(s B. napus L.) and new type of varieties( B. napus L.)or that between new type of varieties( B. napus L.)and nature varieties( B. napus L.).6. Coefficients between the average of gca and yield per plant or HPH of yield per plant were 0.71** and 0.59** respectively. In addition, coefficients between sca and yield per plant or HPH of yield per plant were 0.64** and 0.52** respectively. Strong heterosi can be gained from the combinations whose average of gca or sca were high. For example, yield per plant was the highest of 30 combinations, the average of general combining ability and SCA of that were both the biggest of 30 combinations.7. Coefficients between genetic distance based on polymorphism of SRAP markers and yield per plant heterosis was 0.56**, which was significant at 0.01 levels. whereas it was 0.12 based on polymorphism of SSR markers, which was not significant. Thus, for the prediction of yield heterosis, SRAP markers were better than SSR markers.