| The innovation of germplasm resource and its genetic research is the material basis of breeding. Improving the efficiency of breeding by the method of early generation selection can faster breed the better maize hybrid, which is significant for the further maize production and the development of rural economy. Therefore, the maize S2and S4lines derived from a basic population of Adan9, and the corresponding combinations that crossed by different testers of widely used inbred lines from different heterotic groups were selected as experimental materials to analyze genetic variation among maize S2and S4lines by using SSR makers, and the correlations of genetic variation with yield SCA and herosis performance in this study, which would provide references for the breeding of early generation lines and the combination selection. The results were as followed:1. The results of genetic variation among S2lines:A total of61alleles were detected by20pairs of core SSR primers among52S2lines,1-7alleles and1-9genotypes of each pair, average was3.1and4.7respectively. Genetic distance among the52inbred lines ranged from0.038to0.481with an average of0.176.52S2lines were classified into7distinct groups by using the UPGMA cluster method with the genetic similarity coefficient0.76as threshold, in which the A9-22and A9-37were gathered into a cluster independently, however, the other groups or subgroups were basically consisted with the available pedigree.2. The results of genetic variation among S4lines:A total of39alleles were detected by20pairs of core SSR primers among22S4lines,1-3alleles of each pair with average of1.95, and1-3genotypes of each pair with average of2.15.Genetic distance among S4lines ranged from0to0.362with an average of0.195. With the genetic similarity coefficient0.85as threshold, all of the S4lines were classified into4distinct groups by using the UPGMA cluster method. The clustering results were consistent with the groups based on the pedigree.3. Analyzing the different alleles number of genetic variation showed that No.of different alleles among52S2lines was ranged from2to37, and the difference of S2lines which derived from the same S1line was much lower than that of different one. The different allele’s number among22S4lines were ranged from0to23and the difference of S4lines which came from the same S2line was as well as lowers than that of different S2line. Of which no difference was detected between A9-5131and A9-5133, and the same as the relevant testcrosses, which was suspected as the stabilization in early generation. We suggested that S2was a rapid segerageting generation, which should be enhanced to select more excellent plants from elit S2lines in breeding practice. The lines was as stable as generation increasing, therefore, we should keep the different original S4excellent lines and decrease suitably the amount of plants selected from the same line. According to the analysis, the S4lines derived from the corresponding S2lines whose the different allele amont were higher showed the higher different amont, however, the S4lines derived from the S2lines whose different allele amont were lower showed much more lower different amont, it seems to exist an accelerated stable trend, which should be utilized pointedly in breeding program.4. Analytical results of variation of plant height and ear height indicated that average plant height and ear height showed significant difference between S2lines which derived from the same S1, the variation maglitude and variation coefficient of most of S2lines were higher, and the uniformity of those was lower. The plant height of part of S4lines derived from the S2showed significant difference, while the ear height of all S4lines showed significant difference, also the variation of plant height and ear height in S4lines were lower than those of S2, suggested that the uniformity of population improved gradually.5. The correlation analysis results indicated that no significant correlation existed in the two generations between the genetic distance of parents and effect of SCA for yield per plant of corresponding combinations combined by different tester, also no significant correlation between the genetic distance of parents and heterosis of corresponding combinations. Therefore, we could not only pursue the size of the genetic differences between parents as an indicator of parent selection in breeding practice. However, the heterosis of the combinations crossed by testers from the different heterotic groups showed a great difference in this study, suggested that the selection of the heterotic pattern was much more important. |
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