Dissection The Genetic Basis Of Combining Ability Of Yield And Yield Components With A Set Of Maize Introgression Lines

Heterosis has significant contribution on the grain yield improvement of crops. In maize hybrid breeding, inbreds with elite traits were usually used to combine hybrids. In breeding practice it is often found that the performance of hybrids was not only related to the inbreds themselves but also related to their combing ability, and combining ability is essential for hybrid breeding in crops. Although application of combing ability in breeding has been carried out more than70years, the study on its genetic basis has been seldom addressed and it remains unclear at present. Identifying molecular markers associated with this complex trait would help to understand its genetic basis and provide useful information for hybrid breeding in maize.In this study, genetic loci for general combining ability (GCA) and specific combining ability (SCA) were identified under multiple environments by using four TC (Testcross) population by crossing a set of Z3/HB522ILs with4testers from different heterotic groups. GCA and SCA of the traits of yield per plant(YP), kernel weight(KW), plant height (PH), ear height (EH), ear length (EL), ear diameter (ED), row number (RN), kernel number per row (KN), days to silking (DS) and days to pollen sheding (DP) were investigated. Genetic correlations analysis and significant loci comparision between combing ability and the corresponding traits of the ILs per se were also conducted. Results are as follow:1. The ILs were genotyped with215evenly distributed SSRs according to the reference genetic map of IBM2008, there are14introgression segments in each line, the length of the introgressed segments is about9.9cM, and84.6%genetic background was recovered into Zong3.2. The GCA or SCA of the yield and yield related traits varied largely, in general all of the traits in the ILs fit to the normal distribution. The GCA of YP was positively and significantly correlated to the GCA of KW, EL, ED and RN in all the environment (0.40≦r≦0.77). In general, the SCA of YP was positively and significantly correlated with the SCA of KW, EL, ED and KN in at least2environments.3. A total of165GCA and210SCA loci were identified, with100GCA and39 SCA loci commonly identified in at least2environments. Totally19GCA loci and25SCA loci for YP,17GCA loci and16SCA loci for KW,10GCA loci and21SCA loci for RN,16GCA loci and18SCA loci for KN,22GCA loci and29SCA loci for PH,9GCA loci and17SCA loci for EH,25GCA loci and35SCA loci for EL,20GCA loci and24SCA loci for ED,11GCA loci and17SCA loci for DS,16GCA loci and8SCA loci for DP were detected. Comparing these GCA and SCA loci,3loci for PH,2loci each for KW, EL, ED and DS,1locus each for RN, KN, EH and DP. This suggesting that the genetic basis of GCA and SCA is generally different.4. For the yield and yield-related traits of the ILs per se, a total of371loci were identified and104of them were detected commonly in at least2environments. In Comparision the GCA loci and the significant loci of the ILs per se, totally26loci,5loci each for PH and DP,4loci each for EH, KN, RN and DS,2loci for EL,1locus for KW, simultaneously controlled GCA and their corresponding traits per se. There were10loci,3loci for EH,2loci each for RN and KN,1locus each for YP, ED and DS were found to be associated with SCA and their corresponding trait per se. Correlationships between the GCA of the traits and their corresponding trait per se were not significant or not strong except for DS, DP, RN, PH and EH (0.22≦r≦0.58), especially for the trait of YP. In addition, SCA was also not significantly or strongly correlated to their corresponding traits per se in the4TC populations (r<0.39). These illustrate that combing ability and their trait per se in the ILs might be genetically controlled by different genetic basis.5. For all of the traits investigated, positive and significant correlation (0.28≦r≦0.69) between the number of significant GCA loci in the ILs and the performance of the corresponding GCA of the ILs were detected, implying that pyramiding GCA loci would have positive effect on increasing the performance of GCA.Results in this study revealed that the genetic basis of combing ability was similar with the agronomic traits, which can be dissected with the method of QTL mapping. In addition, we can pyramid efficient combing ability loci to achieve the goal of improvement of maize inbred lines. Results in this study can provid theoritical support for maize hybrid breeding.