Heterotic Grouping For North China Major Maize Inbreds By SSR Markers

Classifying inbred lines into heterotic groups is an important issue in hybrid maize (Zea mays L.) development. It is not only the basis for utilization of heterosis, but the foundation for establishing corresponding heterotic patterns to enhance the efficiency of hybrid maize breeding. In this research, simple sequence repeats (SSRs) were assigned to investigate the genetic diversity among 99 inbred lines, which were widely utilized in maize breeding program in north China. All these lines were divided into several heterotic groups. It would be helpful to enhance the efficiency of maize breeding in north China. The main results of the study were summarized as follows.(1) Seventy-one SSR primers selected from 79 SSR primers (based on CIMMYT-AMBIONET Service Lab) were used in the genetic diversity investigation of the 99 inbred lines in north China. In total, the seventy-one primers produced 313 polymorphic amplified fragments. The number of alleles per SSR locus averaged to 4.41 with the range from 2 to 9. The polymorphism information content (PIC) for all the SSR primers varied from 0.224 to 0.844 with an average of 0.61. (2) In order to assign the classification results to heterotic groups and combine all the relevant data with those from other labs, 6 domestic common testers and another 6 testers from CIMMYT were adopted in the experiment. The 99 inbred lines were classified into seven groups by UPGMA (unweightied pair group method agrithmetic average) based on GS (genetic similarity) from SSR fingerprinting data, i.e. Lancaster, Ried, Luda red cob and PA, Sipingtou, PB, and Tropical germplasm. The classification accorded with the heterrotic groups determined by the pedigree analysis. Consequently, SSR was proved to be a powerful tool in measuring genetic variation and assigning some pedigree-anonymous inbred lines into the current heterotic groups.(3) Seventy-eight inbred lines used in North-eastern China breeding program were classified into three groups and five sub-groups, Lancaster, Ried, Luda red cob and PA, Sipingtou, PB, and the others. Therefore, the genetic framework of maize breeding program in the North-eastern China and its relationship to the domestic and exotic germplasm were revealed.(4) Through the comparison of the grouping result based on different alleles, it was found that the number of polymorphic locus and the number of SSR primers in the genetic diversity analysis were the most critical factors to the classification. It was recommended as 220 and 50 respectively for the least number of polymorphyic loci and the number of SSR primers to classify heterotic groups.