采用表型性状分析、SSR标记和系谱分析对186个区试及引种试验玉米组合进行遗传多样性分析。结果表明，各组合间20个表型性状都变异在一个较小的范围内；利用筛选出的60对扩增条带清晰、具明显多态性的SSR引物，共检测到608个等位基因，每对引物检测到3~23个等位基因，平均为10.1个；SSR多态信息量（PIC）分布范围为0.5179~0.9256，平均值为0.7826；186个组合的遗传相似系数变幅在0.6067~0.9162之间，平均值为0.7722，相似系数在0.7000以上的组合有16 499对，占96.9%，供试材料分为10类，且88.2%的组合集中在第4、8、10类；51个系谱清楚的组合中有36个（占70.58%）与美国的PN种质有密切关系。以上结果均表明，供试组合相似程度较高，遗传差异较小，遗传基础相对单一，进一步拓展玉米种质遗传基础仍然显得十分必要。
Many maize breeders have been paying attention and efforts to solve the problem of narrow genetic diversity in maize. In order to broaden the genetic basis in maize breeding, it is necessary to know the genetic diversity in the current maize hybrids. There may be two ways to study the genetic diversity in maize hybrids. One is to analyze the hybrids which have been widely applied in production and those in regional tests. Another is to analyze the parents of maize hybrids. Most former studies were directed to evaluate the genetic diversity of the parents and few directed to study the hybrids. In present study, analyses of phenotypic characters, SSR molecular markers and pedigrees were made to study the genetic diversity in 186 maize hybrids that were tested in the regional trials of Sichuan and Southwest China.
The results showed that the variation coefficients of plant height, ear height, days to silking, pollen shedding, ASI, ear length, fertile kernel, kernel depth, cob diameter, ear diameter, rows per ear, kernels per row, ear weight, cob weight, yield per plant, fresh weight per ear, water content, kernel rate, 100-kernel weight and test weight among 186 hybrids were 5.74%, 12.06%, 2.63%, 2.36%, 8.50%, 9.68%, 5.80%, 10.57%, 9.32%, 6.02%, 7.90%, 10.54%, 15.95%, 21.51%, 16.19%, 13.85%, 10.35%, 2.46%, 10.92%, and 4.93%, respectively. There were differences in the variation coefficients of different character, but all of the variation coefficients changed in a small range. Sixty pairs of SSR primer distributed on the ten chromosomes of maize produced stable amplified bands and 608 alleles were detected among the hybrids. The average number of alleles per locus was 10.1 with a range from 3 to 23. The values of polymorphism information content (PIC) for each SSR locus varied from 0.5179 to 0.9256 with an average of 0.7826. The genetic similarities of SSR marker pattern among the 186 hybrids ranged from 0.6067 to 0.9162, with an average of 0.7722. There were 16499 pairs of genetic similarity, in which 96.9% were 0.7000 to 0.9256. The cluster analysis showed that the hybrids could be classified into ten clusters, with 88.2% of the hybrids included in Cluster 4, Cluster 8 and Cluster 10. The analysis of pedigree sources of 51 hybrids showed that 36 hybrids had close genetic relationships with the hybrids of Pioneer Company developed in late 1980s and early 1990s in the United States, such as “Y78599”, “Y7865”, “Y78698”, accounting for 70.58%. Meanwhile 13 hybrids had close genetic relationship with “Y78599", accounting for 8.66%. The genetic similarities of SSR marker pattern among the 51 hybrids ranged from 0.661 92 to 0.8799, with an average of 0.7686. There were 1 196 pairs of genetic similarities ranged between 0.7000 and 0.8796, accounting for 93.80% of all the genetic similarity pairs. The cluster analysis showed that 88.2% of the 51 hybrids were in Cluster 4, Cluster 8, and Cluster 10. It was indicated that the similarity was high and the genetic diversity was narrow among the 186 hybrids. It is necessary to broaden the genetic basis of breeding germplasm in maize.
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