[Genetic diversity analysis of maize recurrent selection populations by SSR marker]

Two cycles of mass (MS) and half-sib (HS) recurrent selection and one cycle of marker-assisted selection (MAS) for yield were carried out in two synthetic maize populations DC0 and XFC0, respectively. The genetic diversity of five maize (Zea mays L.) populations, including basic population DC0 and its developed populations HSC2, MSC2, and basic population XFC0 and its developed populations XFC1, were evaluated by 49 SSR primers, which are averagely distributed on 10 maize chromosomes. On the 49 SSR loci, a total of 185 alleles had been detected in these populations. At each locus, 1 to 7 alleles could be detected, with an average of 3.8. The proportion of polymorphic sites differed in the five maize populations, which were 90.3%, 85.9%, 84.9%, 85.9%, 80.5% for DC0, HSC2, MSC2, XFC0 and XFC1, respectively. Genotypes can be showed by the difference of the alleles detected on the 49 SSR loci. There were totally 430, 392, 377, 399 and 395 genotypes for DC0, HSC2, MSC2, XFC0 and XFC1, respectively. The mean gene heterozygosity calculated from the 185 alleles were 0.660, 0.644, 0.645, 0.662 and 0.655 for DC0, HSC2, MSC2, XFC0 and XFC1, respectively. All these results mean that after selection the ranges of variance of the populations decreased slightly. And the mean genetic distance calculated from the 185 alleles were 0.4695, 0.4696, 0.4698, 0.4836 and 0.4902 for DC0, HSC2, MSC2, XFC0 and XFC1, respectively. There was nearly no difference after selection in both the basic populations. Analyses on the distribution of genetic distance showed that most of the genetic distances in the developed populations were smaller than in the basic populations. But the ranges of the genetic distance were wider after selection in both populations. This result indicated that heterogeneity between some of the individuals in the developed populations increased after several times of recombination and exchange. All these indexes demonstrated that the genetic diversity of selection populations was similar to their primary populations, and genetic variation was maintained during recurrent selection.