Genetic Diversity Analysis Of Maize Populations 'YuSyn5' Based On SSR Marker

In china,the narrow genetic base is one of the major limitative factors for the germplam devemlopment in maize breeding.germplasm enhancement,impovement and innovation is the only way to save the problem.To study the genetic structure and diversity of different populations,even and genetic relation between populations is significantly for the impovement,innovationand rational utilization of germplasm..In our study ,we used six generations Materials by recurrent selection of YuSyn5 as the basic materials,we analized the proportion of polymorphic loci, the average locus heterozygosity, genetic distance, and the types of gene frequencies and genotypes of YuSyn5 by method of SSR. The results showed that YuSyn5 by Comprehensive improved still has a wealth of genetic diversity.The main findings are as follows:1. 115 alleles loci were detected in six generations of YuSyn5 population which improved by recurrent selection by using 35 pairs of SSR primers. Each site have an average of 3.29, the number of C0, C1, C2, C3, C4, M5 alleles are as follows: 90,97,110,103,95,102.Based on the allelic strap and allelic combined strap of 35 pairs of SSR primers, The polymorphic loci and proportion of polymorphic loci of six groups were not same.2/3 of the primers at the six groups the proportion of polymorphic loci were reached to 100%.there are many difference on different groups. Based on the polymorphic loci and the proportion of polymorphic loci ,,Groups after improved such as C1, C2, C3, C4, M5 were still have a wealth of genetic diversity.2. The number and frequency of Round improvement in different cycle groups analysis results show:through recurrent selection, the number and genotypes of the five groups have improved all increase slightly, due to the reasons such as genetic recombination may have a number of new genotypes.3. The results indicate that: There are some differences in heterozygosity of genes that detected by the same primer in different populations.That means the gene frequency of same loci in different populations is unequal ,so it induced that have differences in the speciess and proportion of all kinds of gene types.The average gene heterozygosity of C1,C2,C3 population which were improved by half-Sib recurrent selection are 0.334,0.316,0.314 respectively. There have no significant difference in three cycles. The average gene heterozygosity of C4 population which was improved by half-Sib reciprocal recurrent selection is 0.258, it are a little lower comparing with the frontal round population C3.The average gene heterozygosity of M5 which was improved by mass selection popution is 0.266 , it are a little higher comparing with the frontal round population C4.All the results indicated that that mass selection can keep the genetic diversity of the population , half-Sib recurrent selection Second,and half-Sib reciprocal recurrent selection is lowest relatively.The aerage expect heterozygosity of C0,C1,C2,C3,C4,M5 are 0.4,0.445,0.441,0.45,0.419,0.435, respectively.There are little difference in the average heterozygosity observed and the average heterozygosity expected .It is indicated the YuSyn5 population which improved by recurent selection,has not reached Hardy-Weinberg genetic balance state.It is likely due to the filter of population'recurrent selection and choiceness germplasms.4. The genetic distance is an vital guide line to the measurement of individual in the population .Due to the genetic distance between two neighbored markers in the 90 individual of each populations,the genetic distance is increasing and the Standard deviation,extremum are higher ,comparing the improved populations to the base populations. It is likely due to the filter of the choiceness germplasms in the recurrent selection.They enlarge the genetic distance of much indivedual of the improved populations. Parts of individual'heterozygosity is increasing through time after time's recombine and exchange of the improved populations.the analysis of genetic distance between different cycles of samepopulations showed that,the relation of C0 and C4 is closest,the genetic distance between them is 0.0870, and the relation of C0 and C1 is second,the genetic distance between them is 0.0909,and the genetic distances with C3 and M5 are 0.1099,0.1146 ,respectively.the relation of C0 and C2 are farthest,the genetic distance between them is 0.1357. The possible reason for this result is that in the course of recurrent selection the improvement groups of different rounds we have gained in accordance with the phenotype and the standard of combining ability,and the choose of the groups result in the gene locus which we have checked in this experiment partly changed.The genetic distance is relatively far showed that the same gene locus associated with on the basis of the phenotype and the selection of combining ability are little, genetic distance is relatively near, showed that are more.