水稻育成品种遗传基础的宽窄及品种间遗传距离的大小是品种能否在当地有效推广种植的关键因素，同时也是水稻杂交育种中选配亲本的基础。多元统计分析方法常用来测定品种间的遗传差异，了解亲本间的遗传距离。试验以宁夏引黄灌区历年主栽或新选育的水稻品种为材料，分别考查了20个水稻品种的12个主要农艺性状，对均达显著和极显著差异的12个性状进行了主成分分析，由主成分分析中提取的公因子进行聚类分析，并计算各类群主要性状的平均值，得出各类群品种的分类特点。结果表明：20个水稻品种的12个主要农艺性状可归结为5个主成分，经聚类分析，可将20个水稻品种选定合适的阈值后划分为4个类群，表现出遗传距离较近，遗传基础狭窄的特点，并且宁夏水稻品种主要集中在第4类群。因此，在确定水稻育种杂交亲本选配时，要综合考虑主成分互补，且要在类群间进行，并结合米质的选择，则有望选育出农艺性状优良、优质、高产的新品种。但改良品种个别性状时，亲本之一符合育种目标，另一亲本也可选用遗传距离不大的品种。

主成分分析结果表明:第一主成分为产量因子,其贡献率为41.3%;第2主成分为株高因子,其贡献率为20%;第3主成分为外叶数因子,其贡献率为11.8%;第4主成分为叶球横径因子,其贡献率为9.1%;第5主成分为球叶数因子,其贡献率为7.5%,这五个主成分的累积贡献率达89.7%.本试验利用主成分析结果,采用毛重、株高、外叶数、叶球横径、球叶数等5个性状对48个品种进行聚类分析,共将其分为六大类.在优势育种中,双亲应在遗传距离远的类间进行选择,这将有利于提高杂种优势利用的效果.在类内选择亲本,则有利于对目标性状的改良,适合于重组育种,特别是自交系的选育.

The simple sequence repeat (SSR) or microsatellite marker is currently the preferred molecular marker due to its highly desirable properties. The aim of this study was to develop and characterize more SSR markers because the number of SSR markers currently available in tomato is very limited. Five hundred DNA sequences of tomato were searched for SSRs and analyzed for the design of PCR primers. Of the 158 pairs of SSR primers screened against a set of 19 diverse tomato cultivars, 129 pairs produced the expected DNA fragments in their PCR products, and 65 of them were polymorphic with the polymorphism information content (PIC) ranging from 0.09 to 0.67. Among the polymorphic loci, 2-6 SSR alleles were detected for each locus with an average of 2.7 alleles per locus; 49.2% of these loci had two alleles and 33.8% had three alleles. The vast majority (93.8%) of the microsatellite loci contained di- or tri-nucleotide repeats and only 6.2% had tetra- and penta-nucleotide repeats. It was also found that TA/AT was the most frequent type of repeat, and the polymorphism information content (PIC) was positively correlated with the number of repeats. The set of 19 tomato cultivars were clustered based on the banding patterns generated by the 65 polymorphic SSR loci. Since the markers developed in this study are primarily from expressed sequences, they can be used not only for molecular mapping, cultivar identification and marker-assisted selection, but for identifying gene-trait relations in tomato.

Previously isolated tomato ( Lycopersicon esculentum) microsatellite markers were mainly clustered in the centromeric heterochromatin and not located in euchromatic regions. To achieve a more-uniform distribution of microsatellite markers for genome mapping purposes, a set of tomato microsatellite markers containing dinucleotide simple sequence repeats were developed by screening genomic libraries enriched for single-copy sequences, and screening the tomato EST database. The tomato microsatellites isolated in these ways were characterized by combinations of different types of repeated motifs and they were polymorphic in a set of L. esculentum varieties detecting up to four alleles. A total of 20 markers were placed on the genetic map of tomato. Interestingly, all markers isolated from genomic libraries enriched for single-copy sequences by PstI-pre-digestion mapped into the centromeric regions. The majority of markers derived from EST sequences contained predominantly AT microsatellites and were located in euchromatic regions.