Sorghum {Sorghum bicolor L. Moench. } is one of the world's most important cereals. There are a-bout 19 000 seed accessions of sorghum in national genebank of China now. One of the main challenges for gene-banks is the maintenance of the genetic integrity of seed accessions. The study of genetic integrity of sorghum as often cross-pollinated crops has not been reported yet. In order to assess genetic integrity of sorghum correctly, firstly, it is supposed to determine the sample size. Molecular markers are supposed to be the most effective genetic tools for the actual estimate of genetic integrity and microsatellites or simple sequence repeats (SSRs) are one of the most commonly used markers in genetic diversity assessment, population structure studies and marker-assisted selection. To determine the optimal sample sizes of genetic integrity of sorghum , in our study, ten groups of different sample sizes of sorghum (10,20,30,40,50,60,70,80,90,100 individuals per group) were set by random selections and 25 polymorphic microsatellite primers were used to assess the genetic diversity indexes (the average number of alleles, effective number of alleles ,Shannon index,observed heterozygosity .expected heterozygosity, percentage of polymorphic loci and the frequency of rare alleles). Correlation between genetic diversity indexes and sample sizes were analyzed and the results demonstrated that the number of alleles, effective number of alleles, Shannon index increased dramatically with the increase of sample sizes within 40 individuals, and they increased slowly and reached a plateau when more than 40 individuals analyzed. Forty individuals represented 98. 5% of total numbers of alleles,99. 1% of total effective numbers of alleles and 98. 5% of total Shannon indexes of 100 individuals. With the number of alleles, effective number of alleles, Shannon index and the frequency of rare alleles as genetic diversity indexes in the study of sorghum genetic integrity, determination of the sample sizes reached consistency. Therefore, we suggest that the optimal sample size for the study of sorghum integrity with microsatellites analysis is 40 individuals. This study will facilitate the study of genetic integrity of sorghum.%采用微卫星分析高粱不同样本量对遗传多样性指数的影响,从而确定最佳样本量,为遗传完整性研究奠定基础.试验设置了10个样本量梯度,对群体的等位基因数目、有效等位基因数目、香农指数、观察杂合度、预期杂合度、多态位点百分数和稀有等位基因频率的变化趋势进行了分析.结果表明,10～40个样本量范围内,等位基因数目、有效等位基因数目、香农指数、多态位点百分数随着样本量的增大而增大；在40个样本量时,等位基因数目、有效等位基因数目和香农指数达到较高值,分别代表了100个群体98.5％的等位基因数、99.1％的有效等位基因数和98.5％的香农指数,之后样本量继续增加,各指标变化不显著.稀有等位基因频率在40个样本量以上,随着样本量的增加数值变化很小.以稀有等位基因频率、等位基因数、有效等位基因数和香农指数为多样性指标,在高粱遗传完整性研究中样本量大小的确定上达到一致性.因此,建议在用SSR技术对高粱进行遗传完整性分析时,样本量要选择40个单株以上.
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