Biochemical affinities between Cucumis hystrix Chakr. and two cultivated Cucumis species (C. sativus L. and C. melo L.) based on isozyme analysis

Isozymes of eight enzymes in Cucumis hystrix Chakr. and two cultivated Cucumis species (C. sativus L. and C. melo L.) were analysed electrophoretically to investigate the biosystematics of these three species. Cluster analysis using data from six enzymes indicated that considerable genetic distance existed between both C. hystrix and melon and between C. hystrix and cucumber. C. hystrix might be a key species for studying the evolution and taxonomy of genus Cucumis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development and Characterization of Microsatellite Markers from an Enriched Genomic Library of Cucumber (Cucumis sativus)

The development, characterization and application of cucumber ( Cucumis sativus L.) microsatellite markers was accomplished using a library-enrichment procedure. Fifty-seven primer pairs flanking the microsatellite repeats were used for DNA amplification. Sixteen C. sativus accessions were assessed for polymorphisms using 45 primer pairs. The average number of alleles per locus was 3.6, and up to seven alleles were found at one locus. The maximum polymorphism information content value was 0.78 with an average of 0.47. The cucumber microsatellite makers could be useful for seed purity control in hybridity testing. Some of these cucumber markers were transferable to other cucurbit species (i.e. melon, watermelon, pumpkin and bitter gourd).     

Diversification and genetic differentiation of cultivated melon inferred from sequence polymorphism in the chloroplast genome

Molecular analysis encouraged discovery of genetic diversity and relationships of cultivated melon (Cucumis melo L.). We sequenced nine inter- and intra-genic regions of the chloroplast genome, about 5500 bp, using 60 melon accessions and six reference accessions of wild species of Cucumis to show intra-specific variation of the chloroplast genome. Sequence polymorphisms were detected among melon accessions and other Cucumis species, indicating intra-specific diversification of the chloroplast genome. Melon accessions were classified into three subclusters by cytoplasm type and then into 12 subgroups. Geographical origin and seed size also differed between the three subclusters. Subcluster Ia contained small-seed melon from Southern Africa and South and East Asia and subcluster Ib mainly consisted of large-seed melon from northern Africa, Europe and USA. Melon accessions of subcluster Ic were only found in West, Central and Southern Africa. Our results indicated that European melon groups and Asian melon groups diversified independently and shared the same maternal lineage with northern African large-seed melon and Southern African small-seed melon, respectively. Cultivated melon of subcluster Ic may have been domesticated independently in Africa. The presence of 11 cytoplasm types in Africa strongly supported African origin of cultivated melon and indicated the importance of germplasm from Africa.     

Incompatibility in diploid and tetraploid crosses of Cucumis sativus and Cucumis metuliferus

The African horned cucumber (Cucumis metuliferus Naud.; 2x = 2n = 24) contains genes that can confer resistance to many important cucumber (C. sativus L.; 2x = 2n = 14) pests [e.g., root-knotnematode, Meloidogyne incognita (Kofoid & White) Chitwood]. Cucumber is highly susceptible to this root-knot nematode species, and a recent screening of C. sativus accessions in the U.S. National Plant Germplasm collection did not identify sources of resistance. Thus,autotetraploids of Cucumis sativus and C. metuliferus were created to recover fertile resistant interspecific progeny. Autotetraploids were obtained at the highest rate when seeds were immersed in 0.5% colchicine for a period of 6 to 8 hrs. Treatment durations less than 6 hrs produced few tetraploids, and durations of 10 hrs or more were lethal to seeds or developing seedlings. Crosses between C. sativus and C. metuliferus were made using diploid and tetraploid lines in all possible combinations, including reciprocals. Fruit development occurred in crosses when diploid and tetraploid C. sativus were used as the female parent. However, seeds developed only in fruit of C. sativus (4n) ×C. metuliferus (2n) crossings. Seeds from these crosses, however,were flat and not viable. No fruit development occurred in crosses whereC. metuliferus was used as the female parent. This revised version was published online in August 2006 with corrections to the Cover Date.     

SSR标记在甜瓜中的研究进展

SSR（simple sequence repeat）标记是建立在PCR基础上的一种新型DNA分子标记。由于SSR具有丰富的多态性,随机分布于甜瓜的整个基因组中,并表现为共显性,所以它是进行甜瓜遗传研究的理想工具。本文就SSR标记在甜瓜遗传多样性分析,构建遗传连锁图谱、标记和定位目的基因及标记辅助选择等方面的研究进展进行了综述。     

Isolation and characterization of microsatellites in Bambusa arundinacea and cross species amplification in other bamboos

Isolation and characterization of microsatellites was analysed in Bambusa arundinacea and cross species amplification studied in other bamboos. Microsatellites, tandem repeats of short nucleotide (1–6 bp) sequences, are the DNA marker of choice because of their highly polymorphic, ubiquitous distribution within the genome, ease of genotyping through Polymerase chain reaction, selectively neutral, co‐dominant and multiallelic nature. Six microsatellites, three polymorphic and three monomorphic have been characterized for the first time in a bamboo species, Bambusa arundinacea belonging to the family Poaceae. The numbers of alleles per locus ranged from 2 to 13. Cross species amplification was tested in 18 other bamboo species. Monomorphic simple sequence repeats (SSRs) were found to be cross amplified in most of the species tested and polymorphic ones in only three to four species. The utility of SSR loci in a genetic diversity study of B. arundinacea and other cross‐amplified bamboo species has been discussed. This study will help in population genetic studies in bamboo species.     

西瓜和黄瓜乙烯受体ETR1基因片段的克隆与序列比较分析

乙烯受体基因ETR1是乙烯信号转导过程中的关键调控基因.研究根据ETR1基因的保守序列设计引物,以西瓜(Citrullus lanatus (Thunb.) Matsum & Nadai var.lanatus)和黄瓜(Cucumis sativus L.)的基因组DNA为模板进行PCR扩增,获得序列长度分别为1 633 bp和1 491 bp的基因片段CLETR1和CSETR1.序列分析表明,CLETR1和CSETR1与Genebank中收录的多条ETR1基因的核苷酸序列同源性在80%～98%,氨基酸序列同源性在75%～98%.西瓜和黄瓜ETR1基因片段的编码序列存在明显的单核苷酸变异,共23个核苷酸位点存在SNPs(Single nucleotide polymorphisms),其中5个SNPs导致4个编码氨基酸的改变.     

Random amplified polymorphic DNA analyses of cytoplasmic male sterile and male fertile Pigeonpea (Cajanus cajan (L.) Millsp.)

Randomly amplified polymorphic DNA (RAPD) markers were used for the identification of two pigeonpea cytoplasmic genic male sterile (CMS) lines derived from crosses between the wild (Cajanus scarabaeoides & C. sericeus) and the cultivated species of Cajanus cajan. The male sterile (A) line and its maintainer (B) line could be easily differentiated with certain random primers. The two male sterile (288 A and 67 A)systems are based on C. scarabaeoidesand the other is based on C. sericeus could also be differentiated. Amplification product of 600bp amplified by primer OPC-11 was observed in both the cytoplasmic male sterile lines (288 A and 67A), which was absent in the maintainer lines (288 B and 67 B) and the putative R-line (TRR 5 and TRR 6). CMS lines, putative R lines, other cultivars and wild species under the study could be easily distinguished with the help of different primers. Dendrogram constructed based on the similarity index showed that considerable genetic variation exist sbetween CMS lines, two putative R line and wild species studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of interspecific somatic hybrid cell lines in cultivated jute and their early characterization using jute chloroplast RFLP marker

A strong sexual incompatibility barrier that exists between the two cultivated jute species, Corchorus capsularis and Corchorus olitorius, limits the scope for improvement through genetic introgression. Protoplast fusion was carried out to generate interspecific hybrid cell lines. Cotyledonary cell protoplasts of C. capsularis and anthocyaninpigmented hypocotyl protoplasts of C. olitorius were used in the fusion experiments, which appeared to be visually useful in the early selection of the fused products. A chloroplast DNA (cpDNA) marker was developed in jute, which showed species‐specific hybridization patterns with EcoRI‐digested total genomic DNA of C. capsularis and C. olitorius. This cpDNA marker was used in the characterization of the somatic hybrid cell lines at their early stages of growth. Evidence for the presence of both types of cpDNA in the hybrid cell lines was obtained when the total genomic DNA of 4‐ to 7‐month‐old hybrid cell lines was challenged with the chloroplast DNA marker through Southern analysis. It was shown that the early segregation of the parental chloroplasts did not occur in jute, although this is common in other plant species. The hybrid nature of the fused cell lines could also be identified through peroxidase isozyme analysis. Isozyme banding patterns were complex and varied among the hybrid cell lines.     

Genetics of resistance to <Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> in <Emphasis Type="Italic">Cucumis sativus</Emphasis> var. <Emphasis Type="Italic">hardwickii</Emphasis> R. Alef

The genetics of resistance to Cucumber mosaic virus (CMV) in Cucumis sativus var. hardwickii R. Alef, the wild progenitor of cultivated cucumber was assessed by challenge inoculation and by natural infection of CMV. Among the 31 genotypes of C. sativus var. hardwickii collected from 21 locations in India the lowest mean percent disease intensity (PDI) was recorded in IC-277048 (6.33%) while the highest PDI was observed in IC-331631 (75.33%). All the four cultivated varieties (DC-1, DC-2, CHC-1 and CHC-2) showed very high PDI and susceptible disease reaction. Based on mean PDI, 8 genotypes were categorized as resistant, 13 as moderately resistant, 9 as moderately susceptible and one as susceptible. A chi-square test of frequency distribution based on mean PDI in F₂ progenies of six resistant × susceptible crosses revealed monogenic recessive Mendelian ratio 1(R):3(S) to be the best fit. This monogenic recessive model was further confirmed by 1(R):1(S) ratio as the best fit for back cross with resistant parent and no fit for either 3:1 or 1:1 in the back cross with the susceptible parent. The results revealed that CMV resistance in C. sativus var. hardwickii was controlled by a single recessive gene. Considering the cross compatibility between C. sativus var. hardwickii and cultivated cucumber, the resistance trait can be easily transferred to cultivated species through simple backcross breeding.     

甜瓜SSR引物在西葫芦中的通用性研究

本文分析了25对甜瓜SSR引物在西葫芦基因组中的可转移性,以期为西葫芦分子遗传育种研究提供分析工具。结果表明,约24%的甜瓜SSR引物可在西葫芦基因组中有效扩增。多态性分析发现6对引物中有4对在34份西葫芦种质中可以检测到多态性,等位变异数从3~6不等,平均为4。UPGMA 聚类分析表明,来自市场主栽F1的纯化材料和双单倍体材料之间多样性较差,说明现有栽培品种基因谱较窄;而从国家蔬菜种质资源库引进的材料多样性比较丰富,对这些材料的整理和重新评价有助于发掘新的基因源,为西葫芦杂交育种提供新材料。     

Effect of mentor pollen on pistil-pollen incongruities among species of Cucumis L.

Summary The merits of mentor pollen in certain interspecific hybridizations in the genus Cucumis L. were evaluated. African wild cucumber species Cucumis metuliferus Naud. and C. africanus L. and Asian species C. sativus var. hardwickii Alef and var. sikkimensis Hook, were reciprocally crossed. Pollen tube growth was arrested halfway down the style in all combinations except in C. sativus × C. africanus. Mentor pollen irradiated with 100 and 200 krad grew through the style and into the ovules in all species. Fruitset was obtained in all cases when mentor pollen was used either alone or in mixtures. Fruits set after self pollination with mentor pollen yielded only seeds without embryos.In several crosses, aided by mentor pollen, a number of relatively large seeds (with enlarged embryosac) were obtained. A sample of these embryosacs contained a globular structure like an embryo. Embryosacs with embryo-like structures were explanted on several different media but no development was obtained.     

Occurrence and chromosome number of Cucumis sativus var. hardwickii (Royle) Alef. in South India and its bearing on the origin of cultivated cucumber

Summary Cucumis sativus var. hardwickii (Royle) Alef., the wild progenitor of cultivated C. sativus is reported for the first time from peninsular India. The South Indian specimens showed n=7 bivalents in PMCs. The discontinous occurrence of the wild taxon in the Himalayan regions and peninsular hills and the existence of cultivars of C. sativus adapted to the tropical and temperate climates suggest polytopic domestication of the cultivated forms. The possibility of utilizing this wild germplasm for crop improvement is indicated.     

Different sex phenotypes of Cucumis sativus L. and C. melo L. and their endogenous gibberellin activity

Summary Gibberellins were extracted from seeds and green plants of different sex types of the closely related species Cucumis sativus L. (cucumber) and C. melo L. (muskmelon). Both seeds and green plants of monoecious and andromonoecious lines of C. sativus contained significantly higher gibberellin levels at all growth stages tested than did a gynoecious line. Gibberellin activity in the monoecious and andromonoecious C. sativus line reached a maximum at the growth stage corresponding to flower differentiation at cotyledonary and first leaf axils. Vernalization of seeds of gynoecious plants resulted in increased male tendency correlated with increased gibberellin activity. In contrast, monoecious and andromonoecious lines of C. melo were gibberellin deficient relative to hermaphroditic and gynoecious lines.Journal Article No 5534 from the Michigan Agricultural Experiment Station. This work was supported by a grant from the Herman Frasch Foundation.     

PCR-RFLP analysis of the whole chloroplast DNA from three cultivated species of cotton (Gossypium L.)

Variations of the chloroplast DNA (cpDNA) from three of the four cultivated species of cotton (Malvaceae); Gossypium barbadense L., Gossypium hirsutum L., Gossypium arboreum L. and its synonym Gossypium nanking Meyen., were analyzed. Using specific set of primers, the whole circular cpDNAs from the four test species were amplified. These were subsequently digested with the use of seven restriction enzymes. The amplified fragments of the whole cpDNAs of the diploid cultivated cotton G. arboreum and its synonym G. nanking did not show any differences. However, the allotetraploid cultivated cottons G. barbadense and G. hirsutum, showed some fragment length differences directly visible after amplification and two types of restriction fragment length polymorphism (RFLP), the first appeared as slightly lengthened bands and the other as gain or loss of a restriction site. The results also showed that the chloroplast genomes of the allotetraploid cultivated cottons are highly similar to the diploid cultivated cottons tested in terms of length and digestion patterns. The detected amplified length differences, RFLPs and the restriction sites can be considered as species specific markers for the allotetraploid cultivated cottons, which could be a useful tool for future studies of the cpDNA of the genus Gossypium L.     

黄瓜育种中"血缘"遗传关系分析研究

采用RAPD技术研究了华北型与欧洲温室型品种的杂交后代的遗传漂移情况，同时根据供试亲本材料差异位点谱带在F2的分离情况，进行了初步的遗传分析以及F2个体的基因型分析，目的是以遗传距离和说带基因型为依据，分析在育种过程中判断血缘成分的可能性及基本方法，以便最终能够进行遗传关系控制。     

Effects of Temperature on Pollen Tube Growth and Fruit Set in Reciprocal Crosses Between Cucumis sativus and C. metuliferus

Interspecific hybridization between Cucumis sativus and C. metuliferus may be used to introduce disease resistance into the cultivated cucumber. Hybrid plant development, however, is restricted by strong barriers to crossing. The present study was undertaken to examine temperature effects on pollen tube growth and fruit set in reciprocal crosses between C. sativus and C. metuliferus. When crossing C. sativus×C. metuliferus, at 20°C, pollen tube growth was arrested in the stylar region of the pistil and no fruits containing embryos were found. However, at 23° and 26°C, C. metuliferus pollen tubes penetrated into the C. sativus ovules. The enhanced pollen tube penetration was correlated with improved embryo development. Although pre-fertilization barriers were overcome, post-fertilization barriers caused abortion of hybrid embryo development at the globular stage. No effects of higher temperatures were found in the cross C. metuliferus×C. sativus; Pollen tubes were generally arrested in the stylar region of the pistil.     

Synthesis and preliminary characterization of a new species (amphidiploid) in Cucumis

A successful interspecific hybridization between cucumber (Cucumis sativus L., 2n = 14) and a wild it Cucumis species, C. hystrix Chakr. (2n = 24) was made via embryo rescue. Hybrid plants (2n = 19; 7 from cucumber and 12 from C. hystrix) were sterile, but morphologically uniform. Self-pollination and backcrossing of F₁ hybrid plants to either parent confirmed presence of both male- and female-sterility that were likely caused by lack of homology and improper pairing during meiosis. While the multiple-branching habit, densely brown hairs (on corolla and pistil), orange-yellow corolla, and ovate fruit of F₁ hybrid plants were similar to that of the C. hystrix parent, the appearance of the first pistillate flower was more similar to that of C. sativus parent. The diameter and internode length of the stem, and the shape and size of leaves and flowers were intermediate when compared to the parents. The chromosome number in the hybrid was doubled through somaclonal variation during embryo culture and regeneration process to restore the fertility. Pollen grains were released and fruits with viable seeds matured on fertile, synthetic amphidiploid plants. The results from flow cytometry indicated that, on average, 7.3% of the morphologically unique regenerants had the 4C DNA content of 2.35 pg relative to the 2C DNA content of the original F₁ hybrid at 1.17 pg and, therefore, were likely chromosome-doubled F₁ hybrids (2n = 38). Nutrition alanalysis indicated that the synthetic species had higher protein (0.78%)and mineral (0.35%) content compared to the normal pickling cucumber(0.62% and 0.27%, respectively), and could be considered a new Cucumis crop having a special place in the future agriculture. Preliminarily evaluation indicates that C. hystrix possesses a high level of root-knot nematode resistance, and that this resistance is partially expressed in the interspecific F₁ and chromosome-doubled F₁. This and the fact that the fruit morphology of the fertile amphidiploid differs during the growing season (e.g., short and long fruit) suggest that it could be useful in broadening the germplasm base of cucumber. This revised version was published online in July 2006 with corrections to the Cover Date.     

甜瓜总RNA快速提取

采用改良的Trizol法对甜瓜叶片的总RNA进行了提取,利用琼脂糖凝胶电泳及Quantity One软件分析、紫外分光光度法、RT-PCR及PCR法进行纯度、浓度、RNA完整性检测.结果表明:所提取的RNA完整性好,纯度高,不含DNA污染,为进行RT-PCR及其他分子生物学实验奠定了良好的基础;新鲜叶片比冷冻叶片的总RNA提取容易,结果更稳定;幼叶比老叶的总RNA含量高.