Analysis Of Heterosis And Construction Of Genetic Map In Maize By Using SSR Markers

Among maize(Zea maize L.)breeders, there is a heightened awareness of the necessity for both maintaining genetic diversity for crop improvement and improving the quality of genetic resource management. Restriction fragment length polymorphisms(RFLPs)and isozymes can serve as genetic markers for estimating divergence or diversity; however, the limited number of polymorphic isozyme loci available and the labor intensive and time consuming nature of RFLPs make their use for this purpose prohibitive. Microsatellites, or simple sequence repeats(SSRs), may be a viable and cost-effective alternative to RFLPs and isozymes. Seventeen elite maize inbred lines were assayed for polymorphism at 71 SSR marker loci using polyacrylamide gels. The 384 alleles identified served as raw data for estimating genetic similarities among these lines. The average number of alleles per SSR locus was 5.3 with a range 2 to 12. Polymorphic index content(PIC, a measure of discrimination ability)values varied from 0.278 to 0.896 with an average of 0.672. A cluster analysis place the inbred lines in six clusters that correspond to the heterotic groups determined by their pedigree analysis. The utility of polymerase chain reaction(PCR)-based marker such as SSRs for measuring genetic diversity, for assigning lines to heterotic groups and for genetic finger-printing equals or exceeds that of RFLP markers, a property that may prove a valuable asset for a maize breeding program.The yield and yield heterosis were measured by using 17 inbred lines and 136 hybrids that were produced by 17×17 diallel mating design. Genetic distance was significantly correlated with F1 yield and yield heterosis, the coefficient of correlation was 0.443 and 0.310 respectively. Based on six heterotic groups, the coefficient of correlation between genetic distance and yield increased to 0.682 and that between genetic distance and yield heterosis increased to 0.609. Both are significant at 0.01.Utilizing F₂ population derived from the cross of tall inbred 7922 by dwarf inbred 5003, a molecular genetic linkage map of maize was constructed, on which 85 restriction fragment length polymorphisms(RFLPs)markers and 17 simple sequence repeats(SSRs)markers are distributed among 10 linkage groups and span maize genome about 1854.6 cM with average distance between markers being 20.2cM. 106 F_2:3lines of the population derived from the same cross were grown in a 10×11 simple rectangular lattice design of one-raw plots with two replication and evaluated for plant height(PH). With interval mapping procedure, 5 quantitative trait loci(QTLs)controlling plant height were identified and their genetic effects and gene action were determined. 2 major QTLs with opposite-effect were discovered. One for increasing plant height was ph1 which was located at chromosome 2 and accounted for 51.8ï¼…of the total phenotypic variation, the other for decreasing plant height was ph3 which was located at chromosome 5 and accounted for 38.6ï¼…of the total phenotypic variation. The chromosomal location of ph3 might be same or near to the position of bv1, a dwarf mutant of maize.