Heterosis And Combining Ability Analysis And Heterotic Grouping Among Semi-winter Rapeseed Accessions (Brassica Napus L.)

Brassica napus L. originated from southern Europe and was first introduced to China from the 1930 s to 1940 s from Europe and Japan separately. Nowadays, B. napus is the major cultivar type in China. B. napus exhibited large heterosis and, combining ability and heterosis analysis are two important aspects of heterosis utilization, the magnitude of heterosis and combinig ability determines the utilization of heterosis and helps select good hybrid crosses. Previous studies showed that genetic diversity was the base of heterosis, and the relationship between genetic distance and heterosis should be studied to utilize the heterosis well. With the development of heterosis and breeding theory, hetertic grouping become more and more important in plant breeding programs. In maize, heterotic patterns and heterotic groups have been extensively studied, however, there were few studies of this kind in rapeseed. Therefore, heterotic grouping and the heterotic patterns should be studied in rapeseed to increase efficiency of hybrid breeding.In this study, heterosis and combining ability were analyzied under four different environments using nine parent materils: Zhongshuang no. 9(8C108), Zhongshuang no. 4(8C189)and Jingyou no.1(8D129)came from Hubei provience,Ganza1-F(8C360), Yong1(8D153), Qin7-F(8E001), SH-11(8C343)and 6C(8C272)came from Shaanxi province,KS2185(8E019)came from USA, and five different methods were used to classify the tested inbreds of divise origin in China into heterotic groups, simple sequence repeat and sequence-related amplified polymorphism were used to genotype the parental lines, and the relationship between genetic diversity and heterosis was investigated. The A genome genetic diversity among B. napus, B. rapa and B. juncea accessions was also studied, in order to utilize the specific allele resource among them. The main results were obtained as follows:1. Heterosis and combining ability analysis in B. napusIn this study, all the nine parents and their 36 hybrids resulted from in a diallel mating design were evaluated under four different environments, results showed that more than half of the hybrids outyield than the control variety Qinyou 7, and the highest high-check heterosis(HCK) can reach 24%. The average mid-parent heterosis was 15.79%, the highest value of it was 57.85%. Average high-parent heterosis was 7.79%, the highest reached 54.68%. The parent materials showed obvious heterosis, and highest performance of the three hubrid combinations are 8D129 × 8E001(HCK, 23.56%), 8C189 × 8C272(HCK, 23.31%), and 8D129 × 8C343(HCK, 20.08%),these strong hybrids are expected to be widely used in commercial breeding.Mean squares of both general combining ability(GCA) and specific combining ability(SCA) for all traits reached significant levels. Except for number of primary branches(NB), length of the terminal raceme(LTM), number of siliques of the terminal raceme(NSTR), and number of seeds per silique(NS), other traits all showed significant for the interactions between genotype and environment. Except NB, LTM, NSTR and NS, all other traits showed significant effects for interaction between environment and GCA, and for interaction effects between SCA and environments, only NB, LTM, NSTR, NS and seed yield per plant(SYP) were significant. GCA values were greater than the SCA effect values for all traits. The parental lines 8C343, 8D129, and 8D153 showed positive significant GCA effects for seed yield per plot(SY), and 8C108, 272, and 8E019 positive significant GCA effects for number of siliques per plant(NSP), 8C272, 8D129, 8D153, and 8E019 showed positive significant GCA effects for NS, and 8D129, 8D153 and 8E001 showed positive significant GCA effects for thousand seed weight(TSW). Grifing and SCA Yang's methods were both used to analyze SCA and showed different results.2. Relationships between heterosis, genetic distance and combining abilityThe relationship between parental distances, combining ability and heterosis was assessed and results showed that genetic distance measured by total molecular markers(GDtotal) had little correlation with heterosis. In order to make a better prediction, significant markers and favoring markers were selected from the total molecular markers, and results showed that genetic distance measured by favoring markers(GDfavor) significantly and positively correlated with NS, TSW, SYP, and SY for HCK and GCA. Morphological distance was highly and significantly correlated with HCK for TSW and oil content(OC). Interestingly, high correlations were found between SCA and heterosis, and SCA-Yang showed higher correlations with heterosis than SCA. Moreover, high correlations were found between GCA(f+m) and heterosis, which indicated using the information of GCA(f+m) to predict heterosis appeared an important method in rapeseed.3. Heterotic grouping and the heterotic patternFive different methods, including SCA method, molecular markers method, heterotic group specific and general combining ability(HSGCA), SCA-Yang's and heterotic grouping based on GCA of multiple traits(HGCAMT) methods were firstly used in rapeseed heterotic grouping in this study. Nine elite inbreds were classified into different heterotic groups. Different methods made different results, with regard to grouping of inbreds and breeding efficiency, the SCA-Yang's method was the most promising one, followed by the SCA and molecular marker methods. Using the SCA-Yang's method, three opposing heterotic groups [(8C108, 8C189, and 8D129),(8C343, 8C360, 8E001, and 8E019), and(8C272 and 8D153] were identified across four environments, and three testers(8D129, 8C343, and 8D153) corresponding to three groups were identified across environments. These testers will be used to classify other inbreds into different groups in the future.4. Assessment of the A genome genetic diversity among B. napus, B. rapa and B. juncea accessionsThis investigation was aimed at evaluating the genetic diversity of 127 accessions of B.napus, B. rapa and B. juncea by using 15 the A genome specific simple sequence repeat markers selected from 192 pairs of SSR markers. A total of 58 polymorphic fragments were detected by the selected 15 SSR markers. The average number of polymorphic fragments detected by each primer was 3.87, ranging from 2 to 7. The polymorphism information content value ranged from 0.173 to 0.831, with a mean of 0.567. The result indicated that 36.86% of the variance was due to significant differences among populations of species, which indicated that abundance genetic diversity exsited among the A genome of B. napus, B. rapa and B. juncea accessions. The pairwise Fst values of three species ranged from 0.3491 to 0.4192, which are all significant. The highest pairwise Fst value was observed between the B. juncea accessions and the B. napus accessions, which indicated they have the farthest relationship. Keeping the above in view, B. rapa and B. juncea can be used to broaden the genetic base of B. napus as the aboundent diversity among them.