Abstract: 【Objective】The biparental mass selection was used to improve the tropical population Pop. 32 for 5 cycles for photoperiod sensitivity in Sichuan Povince, China.【Method】Phenotype analysis and SSR molecular markers were used in this research.【Result】Results showeds that the traits of flowering were significantly improved after 5 cycles of mass selection. The phenotypic variation coefficients of most of the traits decreased with the advances of generation of selection. With the 40 pairs of SSR markers used, a high level of genetic diversity was in C0 population, a total of 418 alleles were detected in the populations. Some 88.5% of the genetic diversity were estimated intra-populations and 11.5% were estimated inter-populations. The inter-population's genetic diversity was much more than the intra-population's, and the genetic diversity within populations declined with the advances of generation of the selection. The number of polymorphic loci of per population and the ratio of polymorphic loci were also declined as selection. The genotypic numbers of Pop32.C0 was 418, which was the most but the frequency was dispersed. The genotype of Pop32 C4 and Pop32.C5 were small and the frequencies were concentrated. 【Conclusion】The results suggest that the genetic variation declined slowly is possible due to the continuous artificially selection for the early silking and the genetic drift induced by selection intensity or smaller effective population size.

Key words: Maize, Mass selection, Response to selection, SSR markers, Traits