Genetic variability in modern crops is limited due to domestication and breeding. To investigate genetic variation in different populations, 216 tomato (Solanum lycopersicum L.) cultivars, hybrids, and elite breeding lines from four breeding programs were genotyped using single nucleotide polymorphism and simple sequence repeat markers. Of 47 markers analyzed, 72.3% were polymorphic in the whole collection of 216 genotypes and 51.06 59.57% showed polymorphisms in individual populations. However, genetic variation was narrow in all four populations, Nei's genetic distance varied from 0.0422 to 0.1135 between populations and from 0.0085 to 0.3187 between lines in individual populations. Cluster and principal coordinate analysis indicated that the four populations could be grouped into three clades. Lines from Shenyang Agricultural University and China Agricultural University population formed the first clade, lines from Beijing Vegetable Research Center were in the second clade, and lines from Nunhems were in the third clade. This was further supported by population structure analysis using STRUCTURE2.2, and suggested that a lack of germplasm exchange might exist among breeding programs. It rnight be the reason that the progress of developing new varieties with significant improvement of horticultural traits in China is slow in recent years.

Yellow flesh color in tomato is believed to be caused by abnormal transcript of phytoene synthase gene 1 (Psyl). However, our initial work indicated that a yellow fruited line PIll 4490 might have full length of genomic DNA sequence for Psyl. To understand the genetics of flesh color in PI114490, we crossed this line to red fruited lines, 0H9242 and LA3189, to develop F1 and F2 progenies, and sequenced the genomic DNA fragnlent of Psyl from Pll14490 and 0H9242. All F1 plants had red fruits, and F2 populations segregated as 3: 1 for red and yellow, indicating that one single recessive gene controlled the yellow flesh color in PI114490. This gene was allelic to the known r gene based on tests between PI114490 and four r mutants LA2056, LA3003, LA0353, and LA3532. Sequence analysis indicated that Pil14490 had a complete genomic DNA sequence for Psyl gene with only one nucleotide difference in the fourth intron: G in PI114490 and A in 0H9242. This substitution was associated with yellow flesh in the F2 population. There was no detectable or very low lycopene in PI114490 and all yellow fruited F2 individuals. Lycopene in the F1 (9.77 mg/100 g) was higher than the mean (6.52 mg/100g) of two parents, and ranged from O to 11.69 mg/100g in all red fruited F2 individuals. These results suggested that lycopene content was quantitatively inherited.

番茄疮痂病是世界上所有番茄种植地区主要的细菌性病害之一，该病能引起严重的产量损失和品质下降，几十年来一直受到育种界的关注。由于该病病原菌存在多个种和小种以及对该病的抗性呈数量性状遗传，因此通过育种途径来改良抗性进展缓慢。分子标记辅助选择为育种家筛选、聚合或累加对多个小种的抗性提供了一种工具。以前的综述对1997年以前在病害的发生、症状、危害、综合防治、遗传分析和育种等方面的研究进行了较为详尽的总结。近年来，在病原菌种与小种的鉴定、抗源的发掘抗性遗传的分子定位和分子标记辅助选择方面的研究取得了很大进展，传统育种与分子生物学方法有机结合的策略也初见成效。本文将对这些进展进行总结，并对分子标记在番茄疮痂病抗性育种中的应用前景进行讨论。