利用SSR分子标记分析控制双亲混合选择改良玉米窄基群体的遗传多样性

Using SSR Markers to Analysis the Genetic Diversity of Descendants from a Narrow Base Maize Population Developed by Biparental Mass Selection

以玉米群体P4C0及其经过5轮控制双亲混合选择的改良群体为材料，利用SSR分子标记分析其遗传多样性变化。结果表明，经2-3轮选择后，从总体上看，群体多态位点数、多态位点比例、群体内单株间遗传距离、基因杂合度和遗传多样性指数等遗传多样性参数并未发生明显的变化，而进行5轮改良后，虽然每轮减小幅度较小，但累计减少较多。群体基因型数总体上是减小的趋势，但不同地点改良群体基因型数表现减少与增加交替出现的现象。以上结果表明，在改良低代，群体遗传多样性得到了较好的保持，而多代改良则可能会导致群体遗传多样性的下降；在不同生态条件下进行穿梭式群体改良，对加快改良进程，保持群体遗传多样性和提高选择效率都有一定的作用。

Five cycles of biparental mass selection （ MS ） were carried out in a narrow base synthetic maize population namely P4C0. The genetic diversity of 6 maize populations,including the basic population and the devel-oped populations,were evaluated by 51 SSR markers. The results showed that the number of polymorphic loci,the percentage of polymorphic loci,the mean genetic distance,the expected heterozygosity （ He） and the Shannon ge-netic diversity index （ I） displayed a descending trend with the advance of selection,while the change after 2 to 3 cycles were not significant. After 5 cycles,the cumulative reduction is larger although the decrease were slight for per cycle. The number of genotypes selected also decreases with selection presented the trend of declining with the advance of selection and related to the location where the populations were developed. It concluded that the genetic diversity maintained in early generations,especially in the 1st and 2nd cycles,while it declined in advance cycles of MS. The alternative improvement of population in different ecological environments was advantageous to the selection of favorable genes.