A Comparative Research Of Combining Ability Of Main Characters And Yield Heterosis On Maize S₂and S₄Lines

Maize is a major cereal and forage crop, and the fine variety of maize has vital significance in the development of maize production and the increace of grains and farmers’income. The long period and low efficiency of conventional maize breeding method cannot meet the needs of the update varieties in modern corn production. The generation progress can be speed up, and the maize breeding efficiency can be improved through early generation test and directional selection.Therefore,108S2testcrosses and44S4testcrosses, combined with54S2lines,22S4lines derived from Adan9and the testers Zheng58, Chang72and P178selected according to heterotic pattern respectively, were selected as experimental materials in this study. The experiments were conducted in Shuangliu and Yaan respectively, to analyze the combining ability of main characters, yield heterosis and the variation rules in different generations, discuss the correlation between heterosis and SCA of yield, and provide the evidence for directive breeding of the combinations and inbred lines in early generations. The main results were as follows:1. The analyses of specific combining ability (SCA) effects estimated by3kinds of methods in different generations showed that, there were differences of the yield SCA effect size and the positive or negative direction among different combinations combined with the same tester and different S2and S4lines, in which the SCA variation range of yield and100-kernel weight of S4combinations were larger than that of S2calculated by Yang’s simple method with single tester, while SCA of the other characters that estimated by different methods showed difference. According to the SCA effect values of yield calculated by3methods, the SCA effects of most combinations, which calculated by Yang’s simple method with single tester were larger, followed by Yang’s simple method, and then Sprague method.The SCA effects changed regularly between generations calculated by Yang’s simple method with single tester, in which, the higher yield SCA of combinations for S2generation, the bigger probabilities of producing of that of derivative S4, while the lower yield SCA of combinations for S2generation, the smaller probabilities of producing the higher one of corresponding S4, suggested that SCA effect value estimated by Yang’s simple method with single tester could be used as a target in early combination selection. 2. The analytical results of yield heterosis over CK in different generations indicated that the yield heterosis of different combinations, which combined with the different S2and S4lines and2testers respectively were different. In the S2combinations which come from different S1lines, the average heterosis of Zheng58series combinations was-4.02-9.60, and that of Chang72was-6.21-14.74. Generally, the S2lines derived A9-5were the best, followed by the A9-2, then the A9-4were worst. In the S4combinations, the average heterosis of Zheng58series combinations was lower with the range of-7.63-10.04, and that of P178was higher with the range of10.62-28.12, suggested that there might be a better heterotic pattern between A9series lines and the inbred lines of PN heterotic group with PI78as a representative. In addition, the higher yield heterosis of combinations for S2generation, the bigger probabilities of breeding that of derivative S4, and vice versa.3. The variation analysis of plant height and ear height showed that CV of plant height and ear height in the most of S4combinations were lower than that of corresponding S2combinations. In this study, only CV of1plant height and4ear heights out of22S4combinations were larger than that of corresponding S2combinations, that means the population uniformity of the early combination increased with the increasing of generation. Moreover, the uniformity of population influenced on the heterosis of S2combinations significantly, but non-significantly on S4; the similar results were obtained from the yield SCA effect values calculated by2kinds of Yang’s simple methods.4. The result of correlation analysis indicated that there was extremely significant positive correlation between yield SCA and heterosis of combinations in the same generation.Between different generations, it existed extremely significant positive correlation of yield heterosis of the corresponding combinations crossed with the same tester; while the yield SCA effect values calculated only by Yang’s simple method with single tester existed the significant positive correlation, and no significant correlation by other kinds of methods. We suggested that was the most reliable in the early combination selection using the yeild heterosis as a critreia, followed by the SCA effect value calculated by Yang’s simple method with single tester.