Study On The Genetic Diversity And Heterosis In Brassica Napus L. From China, Australia And India

For to avoide simplification of Brassica napus L. genetic base, and to breed or raise more elite B.napus L. varieties (such as wide adaptability, high seed yield, good canola quality, and so on), collecting, evaluating, innovating and utiliziong the germplasm of B.napus L. would have theoretical or practical significance. Up to now, obtaining a strong heterosis cross hybrid from a mass of cross-combinations, it is a numerous, time-consuming process. So, searching a simple and effective way to predict F₁ hybrid preformance and to choose the parental exactly, will improve in the hybrid breeding procedure. In this study, using SRAP markers and SSR makers to evaluate the genetic diversity of 48 B.napus L. germplasm from Australia, India and Chian; based on the result of genetic cluster across varieties, choosing 12 parents and raising 36 F₁ hybrids to carry out a set of heterosis-comparing trials, so as to analyze the relationship between genetic diversity and heterosis performance in B.napus L. in molecular level. Main results are as follow:1. Utilizing 69 SRAP random-combination primers and 144 SSR primers, to amplify genome DNA among 48 Brassica napus L. accessions, gain 204 and 195 polymorphical DNA bands, and the rate of efficient primers were 73.91% and 71.05%, respectively. Each primer can amplify 4 and 2.4 polymorphical DNA bands, respectively.2. The correlation coefficient of molecular genetic distance (GD) among 48 accessions of B.napus L. detected by SRAP markers and SSR markers was 0.6135, but the dicision coefficient was quite small (R² = 0.3764). 48 accessions of B.napus L. were clustering into three groups i, ii and iii at the GD 0.495, using UPGMA method and detected by SRAP markers. Whereas by SSR markers, they were clustering into two groupsâ… ,â…¡at the GD 0.4675.3. Utilizing SRAP and SSR markers, the POPGENE version 1.31 soft analyzing results showed that the genetic differentiation was quite great among the provenances of 48 accessions B.napus L. from Australia, India and China. The variance among provenances accounted for the totle variance of provenances was 27.8%, 28.68%, respectively. Whereas within provenances, it was 72.2%, 71.32%, respectively. So, the variance of totle gene diversity in provenances mainly comes from the inside of provenances.4. Using SRAP and SSR markers to detect the private allele in 12 cross-parents, the results showed that there are 8, 8 and 5 alleles in Chinese, Australian and Indian parents, and account for 4.88%, 4.88% and 3.05% of total alleles detected by SRAP markers, respectively. For SSR markers, there are 12, 8 and 6 alleles, and account for 6.94%, 4.62% and 3.47%, respectively.5. Using agronomical trait, SRAP, SSR and yield-related QTLs markers to calculate the genetic distance among 12 cross parents, and construct the genetic dendrogram. For to calculating the genetic distance among 12 cross parents, different methods having different results. There are having highly similarities among DNA marker systems. Whereas the similar degree reached to significant level between agronomical trait and yield-related QTLs markers methods, this shows that there are having certain conjunctions between them.6. Seedling heterosis-comparing trial indicated that the B.napus L. hybrids already have being shown vegetable growth heterosis when in early growing days, mainly exhibiting on quick elongation taproot and hypocotyl, manifold lateral root. For the relationship between traits, taproot length significant correlated to the number of lateral root (r = 0.5935); Fresh weight highly correlated to dry weight (r = 0.9565), but significant correlated to leaf number (r = 0.5814). For the trait mid-parent heterosis performance, fresh weight and dry weight, fresh weight and leaf number, are highly positive correlation; Dry weight and leaf number, assumes marked pertinency.7. Under the two environments, Wuhan and Lanzhou, the mean value and their range of yield-related traits with heterosis performance among 36 F₁ hybrids are all different. The mean square of yield-related traits of 48 test material (12 parents and 36 F₁ hybrids) are all significant at 0.05 level among genotypes or environments. Moreover, on cross-acting effect of genotype and environment, except seed yield per plant, the mean square of others trait are all reaching highly or markedly difference. This shows that the performance of yield-related traits in B.napus L. is easy suffering the influence of genotype or environment.8. Analyzing the relationship among different yield-related traits. In Wuhan, a highly positive correlation was seen between seed yield per plant and plant height with the efficient height of plant branch, the efficient height of plant branch, silique numbers per main inflorescence, silique numbers per plant, silique length. When in Lanzhou, seed yield per plant and first efficient branch numbers with silique numbers per plant, are markedly positive correlated, but a highly negative correlation was seen between seed yield per plant and main inflorescence length.9. Analyzing the correlations between genetic distance and trait performance with heterosis in B.napus L.. The results indicated that using parental genetic distance estimated by five methods (Agronomical trait value, SSR, SRAP, SRAP & SRR, yield-related trait QTLs markers) was difficult to predicting the performance of seedling trait and yield-related trait with mid-parent heterosis. When classifying 36 F₁ hybrids into different types, the genetic distance and seed yield per plant with its heterosis did not have significant correlations based on agronomical trait or molecular markers.10. Curve simulating the relational trend between genetic distance and mid-parent heterosis for seed yield per plant in B.napus L. hybrids grown in Wuhan and Lanzhou. The results showed that, when parental genetic distance in the two extreme range (minimum or maximum), the heterosis of seed yield per plant did not representing. However, in suitable range, the trait of seed yield per plant would performaned strong heterosis. The cross-combinations that exhibited maximal trait value or heterosis performence had bigger and higher genntic distance and the heterozygosity of alleles than the cross-combinations exhibited minimal trait value or heterosis performence.