Genetic diversity assessed by microsatellite markers in sweet corn cultivars

Information on genetic diversity is essential to the characterization and utilization of germplasm. The genetic diversity of twenty-two sweet corn cultivars (seventeen open-pollinated varieties, OPV, and five hybrids, H) was investigated by applying simple sequence repeat markers. A total of 257 primers were tested, of which 160 were found to be usable in terms of high reproducibility for all the samples tested; 45 were polymorphic loci, of which 30 were used to assess the genetic diversity of sweet corn cultivars. We detected a total of 86 alleles using 30 microsatellite primers. The mean polymorphism was 82 %. The highest heterozygosity values (Ho = 0.20) were found in the PR030-Doce Flor da Serra and BR427 III OPVs, whereas the lowest values (0.14) were recorded in the MG161-Branco Doce and Doce Cubano OPVs. The polymorphism information content ranged from 0.19 (Umc2319) to 0.71 (Umc2205). The analysis of molecular variance revealed that most of the genetic variability was concentrated within the cultivars of sweet corn (75 %), with less variability between them (25 %). The consensus tree derived from the neighbor-joining (NJ) algorithm using 1,000 bootstrapping replicates revealed seven genetically different groups. Nei’s diversity values varied between 0.103 (Doce do Hawai × CNPH-1 cultivars) and 0.645 (Amarelo Doce × Lili cultivars), indicating a narrow genetic basis. The Lili hybrid was the most distant cultivar, as revealed by Principal Coordinates Analysis and the NJ tree. This study on genetic diversity will be useful for planning future studies on sweet corn genetic resources and can complement the breeding programs for this crop.遗传多样性信息对于种质资源（germplasm）的鉴定与利用至关重要。本研究采用简单序列重复（simple sequence repeat, SSR）标记，对22个甜玉米品种（17个开放授粉品种（open-pollinated varieties, OPV）与5个杂交品种（hybrid, H））的遗传多样性展开探究。共计测试257对引物，其中160对在所有供试样本中表现出良好的重复性，可用于后续实验；其中45个为多态性位点，最终选取30个位点用于评估甜玉米品种的遗传多样性。通过30对微卫星引物，共检测到86个等位基因，平均多态性比率为82%。PR030-Doce Flor da Serra与BR427 III这两个开放授粉品种的平均杂合度（Ho）最高，达0.20；而MG161-Branco Doce与Doce Cubano两个开放授粉品种的杂合度最低，仅为0.14。多态性信息含量（polymorphism information content, PIC）的取值范围为0.19（Umc2319）至0.71（Umc2205）。分子方差分析（analysis of molecular variance, AMOVA）结果显示，甜玉米的遗传变异主要集中于品种内部（占比75%），品种间的遗传变异仅占25%。基于邻接法（neighbor-joining, NJ）并经1000次自展重复构建的一致性系统发育树，将供试品种划分为7个遗传聚类群。Nei氏遗传多样性指数（Nei’s diversity）的取值范围为0.103（Doce do Hawai × CNPH-1品种组合）至0.645（Amarelo Doce × Lili品种组合），表明供试甜玉米品种的遗传基础较为狭窄。主坐标分析（Principal Coordinates Analysis, PCoA）与邻接系统发育树结果均显示，Lili杂交品种与其他品种的遗传距离最远。本项甜玉米遗传多样性研究，可为未来甜玉米遗传资源的研究规划提供参考，同时可辅助该作物的育种改良工作。