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。

Yang, W., Sacks, E. J., Lewis Ivey, M. L., Miller, S. A., and Francis, D. M. 2005. Resistance in Lycopersicon esculentum intraspecific crosses to race T1 strains of Xanthomonas campestris pv. vesicatoria causing bacterial spot of tomato. Phytopathology 95: 519-527. We used molecular markers to identify quantitative trait loci (QTL) that confer resistance in the field to Xanthomonas campestris pv. vesica-toria race T1, a causal agent of bacterial spot of tomato. An F2 population derived from a cross between Hawaii 7998 (H 7998) and an elite breeding line, Ohio 88119, was used for the initial identification of an association between molecular markers and resistance as measured by bacterial populations in individual plants in the greenhouse. Polymorphism in this cross between a Lycopersicon esculentum donor of resistance and an elite L. esculentum parent was limited. The targeted use of a core set of 148 polymerase chain reaction-based markers that were identified as polymor-phic in L. esculentum × L. esculentum crosses resulted in the identifica-tion of 37 markers that were polymorphic for the cross of interest. Previous studies using an H 7998 × L. pennellii wide cross implicated three loci, Rx1, Rx2, and Rx3, in the hypersensitive response to T1 strains. Markers that we identified were linked to the Rx1 and Rx3 loci, but no markers were identified in the region of chromosome 1 where Rx2 is located. Single marker-trait analysis suggested that chromosome 5, near the Rx3 locus, contributed to reduced bacterial populations in lines carry-ing the locus from H 7998. The locus on chromosome 5 explained 25% of the phenotypic variation in bacterial populations developing in infected plants. An advanced backcross population and subsequent inbred back-cross lines developed using Ohio 88119 as a recurrent parent were used to confirm QTL associations detected in the F2 population. Markers on chromosome 5 explained 41% of the phenotypic variation for resistance in replicated field trials. In contrast, the Rx1 locus on chromosome 1 did not play a role in resistance to X. campestris pv. vesicatoria race T1 strains as measured by bacterial populations in the greenhouse or symp-toms in the field. A locus from H 7998 on chromosome 4 was associated with susceptibility to disease and explained 11% of the total phenotypic variation. Additional variation in resistance was explained by plant matur-ity (6%), with early maturing families expressing lower levels of resis-tance, and plant habit (6%), with indeterminate plants displaying more resistance. The markers linked to Rx3 will be useful in selection for resistance in elite × elite crosses.

试验采用聚乙二醇（PEG）6000溶液模拟水分胁迫条件（0、-0.2、-0.4、-0.6、-0.8 MPa）对包括3份醋栗番茄、4份栽培番茄的变种和2份对照的种子进行萌发试验，结果显示，在-0.4、-0.6、-1.8 MPa水势下，所有材料都不能发芽。在-0.2 MPa水势下，供试材料的发芽能力都比正常水分（0 MPa）下有所下降，且材料间差异显著，NC 84173和LA 4133发芽最差，而PI114490表现最好，可作为耐旱材料用于育种。