Effects Of Population Improvement By Mass Selection On The Different Synthesized Maize Groups

Development is mainly restricted by lack of germplasm resources in China in maize breeding.Many maize breeders have been paying attention and efforts to solve the problem of narrow genetic diversity in maize.This experiment was made with 3 synthesized corn populations and 63 combinations derived form crosses to 7 testers based on an incomplete diallel design.These materials were provided by Sichuan Agricultural University Corn Research Institute and Sichuan Academy of Agricultural sciences,Which were analyzed with SSR markers and field experiments.The incomplete diallel crosses were used to study the major agronomic traits and combing ability.SSR markers were used to study the genetic diversity.The main results were summarized as follows:1.Variance was significant in many obviously traits in the different populations and different cycles.Populations had significant interactions with cycles.The multiple comparison showed that many traits' mean of GP3 and GP5 were significantly higher than GP4,and the mean of cycle 4 populations(C4)were much higher than original populations(C0).2.Variance of the derivatives of GP3,GP4 and GP5 in kernel depth and rows/ear traits were significant at 0.01 level.After 4cycle mass selection,the mean kernel depth and rows/ear were higher in P3C4,P4C4 and P5C4.Genetic gain of kernel depth and rows/ear were2.83%,4.81%,3.67%and8.95%,4.76%,6.30%for GP3,GP4 and GP5,respectively.Plant height and ear height exhibited an increase,and the amplification of GP4 was significantly higher than GP3 and GP5.Significantly correlated responses were found in other traits such as,ear diameter,ear weight,kernel numbers per row,axis diameter,axis weight,and yield per plant.The GP4 genetic gain of yield per plant and ear diameter were higher than GP3 and GP4.GCA variances were significant in all the observed traits except plant height and ear height.The GCA effects of many yield traits were increasing and turned negative to positive with the selection,then they were significant at 0.01 level.It displayed significant indirect responses to mass selection.The magnitude on effect of yield GCA in turn was GP5,GP3,GP4.And then GP4 had excellent GCA on axis diameter and ear weight.There were 17 hybrid combinations which were superiority over CK 8%in yield/plant,13 of the total were three test-crosses(P3C4/P4C4/P5C4×tester) and the other were two test-crosses(P3C2/P5C2×tester).In addition,it can indicated that yield/plant GCA were significant improved by bi-parental mass selection for 4cycles.3.Using 40 SSR loci distributed on 10 chromosomes of maize,287 alleles were detected among the groups.At each locus,the number of alleles varied from 4 to 12,with an average of 7.18.The polymorphic alleles in group GP3 and its derivative P3C4 were a little higher than those of GP4,GP5 as well as their derivatives,respectively.The polymorphic alleles in the derivatives of GP3 and GP5 exhibited an increase.For the genetic similarity coefficients of intrapopulation,the derivatives of GP3 and GP4 increased gradually and there existed no change in those of GP5.The genotypic numbers in the derivatives of GP3 and GP4 showed a decreasing tendency while a little increase was found in those of GP5.With higher mean value,the gene heterozygosities of GP3,GP4 and GP5 varied in a large range,and no obvious changes were observed in those of their derivative.In comparison with their primary group,the genetic diversity indexes in the derivatives of GP3decreased while those of GP4and GP5increased gradually.Considerable genetic variation revealed within rather than among the group.The distribution of within and among the population on GP3,GP4 and GP5 were 96.81%and 3.19%,94.44%and 5.56%,96.07%and 3.93%,respectively.4.The effective allelic number 'Ae' in the derivatives of GP3 decreased,and then increased.Gradually increased and decreased'Ae'were found in GP4 and GPS,respectively. For estimates of the observed heterozygosity 'Ho' and expected heterozygosity 'He',the derivatives of GP3 and GP5 showed no differences and those of GP4 exhibited a little decrease.The 'F' mean of P3C0,P3C2 and P3C4 were -0.24,-0.25,-0.29;P4C0,P4C2and P4C4 were-0.28,-0.29,-0.28;P5C0,P5C2 and P5C4 were -0.25,-0.30,-0.26,respectively.An obvious genetic deviation from Hardy-Weinberg expectation was observed both within and among all the groups with their 'F' being smaller than 0.5.In general,the results above indicated that direct,correlate and indirect response were significant on kernel depth and rows/ear.The traits and combining ability of 3 populations derivatives were available improved by mass selection.The derivatives of GP5 achieved higher genetic variation,and the genetic diversity of the derivatives of GP3 and GP4 had no significant difference.In addition,it can conclude that there existed the different effects of genetic improvement on different maize groups improved by the same method.