Comparative mapping of ZYMV resistances in cucumber (Cucumis sativus L.) and melon (Cucumis melo L.)

Zucchini yellow mosaic virus (ZYMV) routinely causes significant losses in cucumber (Cucumis sativus L.) and melon (Cucumis melo L.). ZYMV resistances from the cucumber population TMG1 and the melon plant introduction (PI) 414723 show different modes of inheritance and their genetic relationships are unknown. We used molecular markers tightly linked to ZYMV resistances from cucumber and melon for comparative mapping. A 5-kb genomic region (YCZ-5) cosegregating with the zym locus of cucumber was cloned and sequenced to reveal single nucleotide polymorphisms and indels distinguishing alleles from ZYMV-resistant (TMG1) and susceptible (Straight 8) cucumbers. A low-copy region of the YCZ-5 clone was hybridized to bacterial artificial chromosome (BAC) clones of melon and a 180-kb contig assembled. One end of this melon contig was mapped in cucumber and cosegregated with ZYMV resistance, demonstrating that physically linked regions in melon show genetic linkage in cucumber. However the YCZ-5 region segregated independently of ZYMV resistance loci in two melon families. These results establish that these sources of ZYMV resistances from cucumber TMG1 and melon PI414723 are likely non-syntenic.     

Comparative analysis of marker-assisted and phenotypic selection for yield components in cucumber

Theoretical studies suggest that marker-assisted selection (MAS) has case-specific advantages over phenotypic selection (PHE) for selection of quantitative traits. However, few studies have been conducted that empirically compare these selection methods in the context of a plant breeding program. For direct comparison of the effectiveness of MAS and PHE, four cucumber (Cucumis sativus L.; 2n = 2x = 14) inbred lines were intermated and then maternal bulks were used to create four base populations for recurrent mass selection. Each of these populations then underwent three cycles of PHE (open-field evaluations), MAS (genotyping at 18 marker loci), and random mating without selection. Both MAS and PHE were practiced for yield indirectly by selecting for four yield-component traits that are quantitatively inherited with 2–6 quantitative trait loci per trait. These traits were multiple lateral branching, gynoecious sex expression (gynoecy), earliness, and fruit length to diameter ratio. Both MAS and PHE were useful for multi-trait improvement, but their effectiveness depended upon the traits and populations under selection. Both MAS and PHE provided improvements in all traits under selection in at least one population, except for earliness, which did not respond to MAS. The populations with maternal parents that were inferior for a trait responded favorably to both MAS and PHE, while those with maternal parents of superior trait values either did not change or decreased during selection. Generally, PHE was most effective for gynoecy, earliness, and fruit length to diameter ratio, while MAS was most effective for multiple lateral branching and provided the only increase in yield (fruit per plant). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

QTL analysis of powdery mildew resistance in cucumber (Cucumis sativus L.)

A population of F₇ recombinant inbred lines (RILs) was made from a cross between susceptible (‘Santou’) and resistant (PI197088-1) lines of cucumber in order to study powdery mildew resistance loci. Susceptibility to powdery mildew in the F₇ RIL individuals showed a continuous distribution from susceptible to resistant, suggesting that powdery mildew resistance is controlled by quantitative trait loci (QTLs). A QTL analysis identified two and three loci for powdery mildew resistance under 26 and 20°C conditions, respectively. One QTL was found in the same position under both temperature conditions. Therefore, it is more likely that one major QTL acts under both temperature conditions and that other QTLs are specific to the two temperature conditions. The above results suggest that the four QTLs are controlled in a different temperature manner, and that their combination played an important role in expressing a high level of resistance to powdery mildew in this cucumber population. Sequence-tagged site (STS) markers associated with each QTL were developed and would be useful for breeding a cucumber line with a high level of powdery mildew resistance. Y. Sakata and N. Kubo contributed equally to this work and are considered as first authors.     

Expression analysis of defense-related genes in cucumber (Cucumis sativus L.) against Phytophthora melonis

Molecular Biology Reports - Phytophthora melonis is one of the most destructive cucumber disease, causing severe economic losses in the globe. Despite intense research efforts made in the past...     

Transformation of cucumber (Cucumis sativus L.) plants with Agrobacterium rhizogenes

Summary Transgenic cucumber plants (Cucumis sativus L., cv. Straight Eight) were regenerated from roots induced by inoculation of inverted hypocotyl sections with Agrobacterium rhizogenes containing the vector pARC8 in addition to the resident Ri-plasmid. The DNA transferred to the plant from the vector (T-DNA) included a gene which encoded the enzyme neomycin phosphotransferase II, and thus conferred on the plant cells resistance to kanamycin. The transgenic plants looked normal and were positive for the neomycin phosphotransferase II. Southern blot analysis of the transgenic plants revealed that all plants contained vector DNA, but only some of them contained DNA from the Ri plasmid.     

Ploidy instability of embryogenic cucumber (Cucumis sativus L.) callus culture

Embryogenic callus cultures were established from immature cucumber(Cucumis sativus L.) embryos on E20A (Dumas de Vaulxet al. 1981) or MS (Murashige and Skoog 1962) media supplemented with 6-benzylaminopurine (BAP), α-naphthylacetic acid (NAA) and/or 2,4-dichlorophenoxyacetic acid (2,4-D). Regeneration of plants was observed after a transfer to culture media either without growth regulators or supplemented with kinetin and NAA. Flow cytometry was employed to estimate DNA ploidy levels. Most of cell nuclei in young leaf tissues were found in G₁ phase with 2C DNA content. Callus cultures were mixoploid with DNA content ranging from 2C to 32C. The frequency of polyploid cells was increasing with the age of culture and the polyploidization was accompanied by a gradual loss of regeneration ability. Plants regenerated from callus cultures were classified as diploid (57 %), tetraploid (18 %), octoploid (4 %) and mixoploid (2n/4n, 4 %) and (4n/8n, 17 %). The results of this study confirmed a close link between the polyploidization and the loss of totipotencyin vitro. Tetraploid plants obtained in this study have a potential to be used in interspecific crosses where their tetraploid status could help in overcoming existing breeding barriers due to differences in chromosome number.     

黄瓜性型分化的分子机制

黄瓜(Cucumis sativus)是雌雄异花植物性型分化研究的重要模式植物,近年来虽然其性型分化的分子机制研究取得了一定的成果,但其性型分化的调控机制尚未完全阐明。该文综合花器官发育基因、性别决定基因、内源激素、环境因子、性型分化假说,在分子水平构建了黄瓜性型分化的表达调控网络。同时对激素和性别决定基因协控的黄瓜单性花器官凋亡机制进行了阐述,并就miRNA在黄瓜性型分化调控中的作用进行了探讨。     

Quantitative trait locus analysis of lateral branch– related traits in cucumber (Cucumis sativus L.) using recombinant inbred lines

A group of 224 recombinant inbred lines (RILs) was derived from a narrow cross between 2 cucumber (Cucumis sativus L.) lines, namely, S94 (Northern China type with weak lateral branch growth potential and early lateral branch sprouting time) and S06 (Northern European type with strong lateral branch growth potential and late lateral branch sprouting time). These lines were then used for investigating lateral branch-related traits. A total of 36 quantitative trait loci (QTLs) were detected for the following 4 lateral branch-related traits: lateral branch average length (LBAL), lateral branch total length (LBTL), lateral branch number (LBN), and first lateral branch node (FLBN). Further, each QTL explained 3.1% (lbtl2.1, spring) to 32.3% (lbn2.3, spring) of the observed phenotypic variance. Eleven QTLs (lbal1.1, lbtl1.1, lbn1.2, flbn1.2, etc.) for different traits were found to be clustered on the e23m18d-ME23EM6c section (7.4 cM) of linkage group (LG) 1; further, 15 QTLs (lbal2.1, lbtl2.1, lbn2.1, flbn2.1, etc.) were found to be clustered on the S94A1-ME4SA4a section (13.9 cM) of LG2. Twenty-one QTLs explained more than 10% of the phenotypic variance. Moreover, lbtl1.3 (autumn, 26.2%, logarithm of odds (LOD) = 17.4; spring, 26.9%, LOD = 17.9) had stable position and contribution in both seasons. Several se-quence-anchor markers (CMBR40, F, CS30, S94A1, CSWTA11B, etc.) were closely linked with some QTLs for LBAL, LBTL, LBN, and FLBN, which can be used for the marker-assisted selection to improve the plant architecture in cucumber breeding.     

A novel role for cyanide in the control of cucumber (Cucumis sativus L.) seedlings response to environmental stress

The effects of potassium cyanide (KCN) pretreatment on the response of cucumber (Cucumis sativus L.) plants to salt, polyethylene glycol (PEG) and cold stress were investigated in the present study. Here, we found that KCN pretreatment improved cucumber seedlings tolerance to stress conditions with maximum efficiency at a concentration of 20 µM. The results showed that pretreatment with 20 µM KCN alleviated stress‐induced oxidative damage in plant cells and clearly induced the activity of alternative oxidase (AOX) and the ethylene production. Furthermore, the structures of thylakoids and mitochondria in the KCN‐pretreated seedlings were less damaged by the stress conditions, which maintained higher total chlorophyll content, photosynthetic rate and photosystem II (PSII) proteins levels than the control. Importantly, the addition of the AOX inhibitor salicylhydroxamic acid (1 mm ; SHAM) decreased plant resistance to environmental stress and even compromised the cyanide (CN)‐enhanced stress tolerance. Therefore, our findings provide a novel role of CN in plant against environmental stress and indicate that the CN‐enhanced AOX might contribute to the reactive oxygen species (ROS) scavenging and the protection of photosystem by maintaining energy charge homoeostasis from chloroplast to mitochondria.     

Acclimation of chlorophyll biosynthetic reactions to temperature stress in cucumber (Cucumis sativus L.)

The adaptive responses of the greening process of plants to temperature stress were studied in cucumber (Cucumis sativus L. cv. Poinsette) seedlings grown at ambient (25 °C), low (7 °C) and high (42 °C) temperatures. Plastids isolated from these seedlings were incubated at different temperatures and the net syntheses of various tetrapyrroles were monitored. In plastids isolated from control seedlings grown at 25 °C, the optimum temperature for synthesis of Mg-protoporphyrin IX monoester or protochlorophyllide was 35 °C. Temperature maxima for Mg-protoporphyrin IX monoester and protochlorophyllide syntheses were shifted to 30 °C in chill-stressed seedlings. The net synthesis of total tetrapyrroles was severely reduced in heat-stressed seedlings and the optimum temperature for Mg-protoporphyrin IX monoester or protochlorophyllide synthesis shifted slightly towards higher temperatures, i.e. a broader peak was observed. To further study the temperature acclimation of seedlings with respect to the greening process, tetrapyrrole biosynthesis was monitored at 25 °C after pre-heating the plastids (28–70 °C) isolated from control, chill- and heat-stressed seedlings. In comparison to 28 °C-pre-heated plastids the percent inhibition of protochlorophyllide synthesis in 40 °C-pre-heated plastids was higher than for the control (25 °C-grown) in chill-stressed seedlings and lower than for the control in heat-stressed seedlings. Maximum synthesis of total tetrapyrroles and protoporphyrin IX was observed when chloroplasts were heated at 50 °C, which was probably due to heat-induced activation of the enzymes involved in protoporphyrin IX synthesis. Prominent shoulders towards lower or higher temperatures were seen in chill-stressed or heat-stressed seedlings, respectively. The shift in optimum temperature for tetrapyrrole biosynthesis in chill- and heat-stressed seedlings was probably due to acclimation of membranes possibly undergoing desaturation or saturation of membrane lipids. Proteins synthesized in response to temperature-stress may also play an important role in conferring stress-tolerance in plants. Received: 8 October 1998 / Accepted: 19 November 1998     

Tissue-culture-responsive and autotetraploidy-responsive changes in metabolic profiles of cucumber (Cucumis sativus L.)

Somaclonal variation commonly occurs during in vitro plant regeneration and may introduce unintended changes in numerous plant characters. In order to assess the range of tissue-culture-responsive changes on the biochemical level, the metabolic profiles of diploid and tetraploid cucumber R1 plants regenerated from leaf-derived callus were determined. Gas chromatography and mass spectrometry were used for monitoring of 48 metabolites and many significant changes were found in metabolic profiles of these plants as compared to a seed-derived control. Most of the changes were common to diploids and tetraploids and were effects of tissue culture. However, tetraploids showed quantitative changes in 14 metabolites, as compared to regenerated diploids. These changes include increases in serine, glucose-6P, fructose-6P, oleic acid and shikimic acid levels. Basing on this study we conclude that the variation in metabolic profiles does not correlate directly with the range of genome changes in tetraploids.     

Virus particles in guttate and xylem of infected cucumber (Cucumis sativus L.)

Particles of plant viruses representing ten genera were visualised by electron microscopy in samples of guttate from systemically infected cucumber (Cucumis sativus L.) plants. For the majority of viruses tested, guttation samples tested positively by ELISA and infectivity was also demonstrated. Virus particles of zucchini yellow mosaic potyvirus were also observed in xylem in sections of infected root tissue. Since guttate originates from xylem exudate, this study demonstrates the potential for xylem tissue to act as a conduit for a diverse group of plant viruses in planta     

Inheritance and linkage relationships of isozyme loci in cucumber (Cucumis sativus L.)

Summary Genetic analyses were conducted among 18 provisionary isozyme loci in Cucumis sativus L. Fourteen loci demonstrated simple Mendelian inheritance while observed variation at four loci (Gpi2, Gr2, Pgm3, Skdh2) was determined not to have a predictable genetic basis. Joint segregation analyses among the 14 genetically predictable polymorphic loci resulted in the assignment of 12 loci to four linkage groups. Linkage groups contain the following loci: (1) Gr1, Pgm1, Idh, Pgd1; (2) Pep-pap, Mdh2, Mdh3, Gpi1; (3) Pep-la, Per4; (4) Pgd2, G2dh. Mpi2 and Mdh1 segregated independently. Recombination fractions for linked loci ranged between 0.051 (Pgm1-Idh) to 0.385 (Pep-la-Per4). Some practical applications of isozyme marker loci for cucumer improvement are discussed.     

Aluminium effect on nitrate assimilation in cucumber (Cucumis sativus L.) roots

In vivo effect of aluminium on nitrate uptake and reduction by cucumber seedlings was investigated. The high-performance liquid chromatography was used to analyse the rate of nitrate uptake. Low (0.5 mM) concentration of AlCl₃ in the nutrient solution stimulated nitrate uptake during the first 3 h. On the other hand, 6 h exposure of the cucumber seedlings to 1 or 5 mM of AlCl₃ resulted in inhibition of nitrate uptake and at 5 mM concentration of AlCl₃ the efflux of nitrate was observed. Furthermore, the amount of nitrate accumulated in cucumber roots after aluminium treatment was decreased. The noteworthy fact was observed, that at all concentrations of aluminium tested on increase of the nitrate reductase activity. This stimulation was concentration depended, but independent of the source of the enzyme. The activity of both the cytosolic and the plasma membrane bound nitrate reductase activity was enhanced in vivo. On the other hand, AlCl₃ applied in vitro only slighty decreased nitrate reductase activity.     

Intercropping cucumber with amaranth (Amaranthus cruentus L.) to suppress populations of major insect pests of cucumber (Cucumis sativus L.)

A study was conducted in 2007 and 2008 to investigate the effectiveness of grain amaranth (Amaranthus cruentus L.) planted at different times in an amaranth/cucumber intercrop to reduce the density of cucumber insect pests. Cucumber varieties, Marketmore and hybrid F_1, were established from seed as a monocrop or intercropped with amaranth, and with amaranth established at two weeks before cucumber (2 WBC) on the same day as cucumber (SDC) or two weeks after cucumber (2 WAC). The population of cucumber beetles and fruit flies was lower with amaranth established 2 WBC and SDC than with 2 WAC. Populations of the insects were influenced by cropping system and time of introducing amaranth. Fruit damage by cucumber beetles and fruit flies was lower with 2 WBC and SDC than with 2 WAC. However, the damage was reduced in the intercrop compared with the monocropped cucumber. With SDC, the reduction was about 75 and 50% in 2007 and 2008, respectively. In intercrops and monocrops, cucumber fruit yield was influenced by the time of inter-cropping; in the mono- and inter-crop, the highest yield was with SDC. The highest land equivalent ratios for cucumber were 1.0 and 0.7 in 2007 and 2008, respectively, with SDC. Planting amaranth and cucumber on the same day (SDC) achieved effective control of cucumber insect pests.