Study On Genetic Diversity And Heterosis In Brassica Napus

Breeding for hybrid is an important way to improve yield in crops. High heterosis was observed in Brassica napus. Many researches showed that hybrids from AsianxEuropean, genetically distinct from each other, had higher yield than hybrids from AsianxAsian or EuropeanxEuropean with similar genetic background. So knowledge of genetic germplasm is helpful for breeding for hybrids with yield potential, and studies on genetic diversity and its relationship to hybrid performance and heterosis would make it possible to predict heterosis and select excellent hybrid efficiently.In this study, genetic diversity in B.napus was analyzed by RAPD technique. Fl performance and heterosis of an incomplete diallel design system (4 CMS lines and 8 restorer lines) in two years (Trial 1,Trial 2) and another incomplete diallel design system (4 CMS lines and 5 restorer lines) in one year (Trial 3) were investigated and analyzed. Genetic diversity among 20 accessions was detected by RAPD and RFLP techniques. Its relationships to hybrid performance and heterosis were also studied. The main results are as followings:1. Analysis of genetic diversity in B.napus1.1 181 polymorphic bands were produced among 50 accessions by 21 strictly selected primers. 50 accessions were divided into three main groups by clustering analysis and principal component analysis. European and Canadian spring type was in one group and European winter type was in another group. All accessions in the third group were from Japan and China. The results indicated that genetic background of many Japanese accessions was similar to Chinese accessions, but were distinguished from Chinese accessions. They could be used to enlarge Chinese germplasm.1.2 190 polymorphic bands were produced among 56 Pol cms maintainers and restorers by 21 random primers. 56 accessions could be clustered in three main group on bootstrap consensus tree. European winter type and European and Canadian spring type were in one group, although they distinguish from each other. This indicated that Pol cms maintainers and restorers had large genetic variance and selection for good quality has not narrowed genetic diversity of Pol cms maintainers and restorers.2. Heterosis, correlation and combination ability analysis of different traits2.1 Combinations in highest yield group or in lowest group were investigated. Combinations in highest yield group usually had high GCA and high SCA, and their average mid-parent heterosis was larger significantly than that in lowest group in Trial 1 and Trial 2. Few combinations in highest yield group had positive special combination ability (SCA) of silique per plant,seeds per silique and weight of 1000 seeds.2.2 Plant yield had highest heterosis, and positive in all combinations. Heterosis of yield and its components was : plant yield > silique per plant > seeds per silique > weight of 1000 seeds. Heterosis was affected easily and different with materials and growing seasons.2.3 Plant yield was positively correlated to silique per plant and seeds per silique, while negatively correlated to weight of 1000 seeds. Three components of plant yield were negatively correlated to each other. Other traits except weight of 1000 seeds were positively correlated in Trial 1 and Trial 2.2.4 Heterosis was significantly (at 1% level) correlated to SCA positively. Plant yield was correlated positively to general combination ability (GCA) at 1% level and to SCA, while closer to GCA than to SCA. GCA was more stable than SCA in two year'trials.2.5 Heterosis in all combinations in two yields was not correlated significantly.3. Genetic diversity and its relationships to heterosis, Fl performance,GCA and SCA3.1 277 amplified and 117 hybridized polymorphic bands were produced by 41 primers and by 11 cDNA probes, respectively. RAPDs detected 21 bands unique to 10 parents, while RFLPs 7 bands to 5 parents (4 of them also had unique RAPDs). Genetic diversity among maintainers and restorers was larger than that within restorers or within maintai...