Heterosis And Genetic Diversity In Rapeseed (Brassica Napus L.)

Heterosis is a common phenomenon in biological kingdom and plays an important role in increasing crop yield. Many researches of crop breeding suggested the genetic distance (GD) between parents showed positive correlations to heterotic phenotypes in some range, more differences of GD between parents and more heterosis. With developing of molecular marker, it proved to be a better tool in understanding the genetic basis of heterosis, including phylogenetic relationship of parents, genetically divergence of parents, as well as GD among various materials. Furthermore, it is possible to understand the relationship between genetic diversity and hybrid performance by molecular markers.In this study, DNA fingerprints were constructed by using SSR and AFLP techniques in 59 Brassica napus inbredlines. The single plant yield and yield component traits were further investigated among 5 POL male sterility lines, 5 restorer lines and 25 F1, using 5×5 diallel cross design. To determine the potential capacity of ten inbreeding lines, combination ability (CA) was examined according to plant yield and yield component traits observed by ten parents and 25 hybrids. Heterosis prediction was also analyzed by molecular markers indicated GD between parents. The main results are as follows:1. Clustering analysis of 59 materials309 polymorphic bands were produced among 59 accessions by 43 SSR markers and 27 AFLP markers. The results of UPGMA (Un-weighted Pair Group Mathematics Average) clustering suggested that 59 accessions were divided into four main groups in 0.57 of genetic similarity: (1) two male sterility lines and their maintainer lines of black seed, as well two restorer lines, (2) all male sterility lines and their maintainer lines with yellow seed coat, (3) another maintainer line and restorer line, (4) the others of 21 restorer lines. The results indicated all of male sterility lines and their maintainer lines were genetically similar, however, the male sterility lines and their maintainer lines of yellow and black seeds were divided into different groups because of their genetic differences.2. Analysis of the major yield traits in F1The results from field experiments showed that seed yield per plant of 25 hybrids had positive mid-parent heterosis which ranged from 1.81%-128.33% with a mean of 50.50%, also they had in plant height and silique per plant. However, silique/plant which is one of the most important factors in yield component traits, and had the highest heterosis, which ranged from 4.27%—81.41%with a mean of 32.94%.3. Analysis of combination abilities for different traitsThe combination ability of parents was analyzed. The results suggested herterosis differed significantly for general combination ability (GCA) of silique per plant, seeds/silique, weight of 1000 seeds and yields per plant in five male sterility lines. Plant yield of 06-6-60(?), 06-6-652(?), P33 and P29' father had the higher GCA. Heterosis was also different for special combination ability (SCA) of silique/plant and seeds/silique.4. Correlation and combination ability of different traitPlant yield was positively correlated to silique per plant, seeds per silique and weight of 1000 seeds; but silique per plant was negatively correlated to seeds per silique, length of silique and weight of 1000 seeds. Plant yield was positively correlated to plant height, length of main inflorescence, number of branches and so on.The MPHs of plant yield, silique per plant and weight of 1000 seeds were positively correlated to general combining ability (GCA), and the MPHs of plant yield, silique per plant and seeds per silique were significantly (at 1% level) correlated to SCA positively.5. The correlation analysis between genetic distance and heterosisLinearity correlation analysis showed that GD was not significantly correlated to hybrid performance of seeds/silique, weight of 1000 seeds and plant yield, also with SCA. Although MPH of plant yield was significantly related to GD, the determination coefficient was low. In conclusion, more work has to be done if we would like to directly predict heterosis using molecular markers genetic distances according to our research.