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Ruth S. Kobayashi, Stephen L. Sinden, and John R. Stommel

Incorporation of genes from wild species has been a major contributor to tomato improvement in recent years. Solanum ochranthum, a woody non-tuber bearing species, is a potential source of resistance against tomato diseases and insect pests but is genetically isolated from tomato. Somatic hybridization methods were developed to facilitate the use of S. ochranthum for tomato germplasm improvement. Leaf mesophyll protoplasts of S. ochranthum and a Lycopersicon esculentum hybrid were chemically fused with polyethylene glycol. The protoplasts were initially cultured in Shepard's CL, a MS based medium, containing 1 mg·1-1 NAA, 0.5 mg·1-1 BAP and 0.5 mg·1-1 2,4-D. Hybrid regenerants and regenerants of the L. esculentum parent were recovered; S. ochranthum did not regenerate. Hybridity was established by morphological characters, peroxidase isozyme and RAPD markers. Use of these somatic hybrids for tomato improvement was evaluated.

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Toshihiko Ikenaga, Seiji Kikuta, Miyuki Kistuki, Midori Yamada, and Kenichiro Nakashima

Solarium aculeatissimum Jacq. contains the steroid saponins aculeatiside A and aculeatiside B at high levels in the root, whereas they are lacking in all organs of tomatoes (Lycopersicon esculentum Mill). We examined the site of synthesis of these steroid saponins by using grafts between S. aculeatissimum and tomato plants. When S. aculeatissimum was grafted onto a stock of tomato (S.a./Tom.), a small amount of steroid saponin was found in the leaves and the stem of S. aculeatissimum but not in the roots of the tomato. However, when tomato was grafted onto stocks of S. aculeatissimum (Tom. /S.a.), steroid saponin occurred only in the roots of S. aculeatissimum. These results suggest that the steroid saponins are mainly synthesized in the roots of S. aculeatissimum. The lack of transport of steroid saponins from the roots of S. aculeatissirnum to the leaves and stem of the tomato remains unexplained.

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John R. Stommel and Kathleen G. Haynes

Fruit of the cultivated tomato (Lycopersicon esculentum Mill.) store predominantly glucose and fructose whereas fruit of the wild species L. hirsutum Humb. & Bonpl. characteristically accumulate sucrose. Reducing sugar and sucrose concentrations were measured in mature fruit of parental, F1, F2, and backcross (BC1) populations derived from an initial cross of L. esculentum `Floradade' × L. hirsutum PI 390514. Generational means analysis demonstrated that additive effects were equal to dominance effects for percentage of reducing sugar. It was determined that a single major gene, dominant for a high percentage of reducing sugar, regulates the percentage of reducing sugar in tomatoes. We propose that this gene be designated sucr. Only additive effects were demonstrated to be important for glucose: fructose ratios. Using L. hirsutum as a donor parent for increasing total soluble solids concentration in the cultivated tomato is discussed.

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Md. Shahidul Islam, S. Khan, and T. Matsui

Sucrose metabolism was followed in developing fruit of domesticated cherry tomato (Lycopersicon esculentum var. cerasiforme Alef.). The high amounts of reducing sugars were consistently linked to high soluble acid invertase (EC 3.2.1.26), whereas sucrose synthase (EC 2.4.1.13) followed the same pattern of sucrose levels and reached a peak of activity during early stage of maturation and then decreased to near nil. In comparison, sucrose phosphate synthase (EC 2.4.1.14) activity remain relatively constant throughout development. Thus, sucrose synthase and acid invertase, rather than sucrose phosphate synthase, are the critical enzymes regulating sucrose accumulation in tomatoes. Cultivated cherry tomato sucrose synthase (UDP-glucose: D-fructose 2-glucosyltransferase) was purified to homogeneity by ammonium sulfate precipitation, anion exchange chromatography on DEAE-Toyopreal 650, and gel filtration on Sephadex G-200. Further purification to homogeneity resulted from a single band from SDS-PAGE. The enzyme was identified as a homotetramer with a total molecular mass of 370 kDa and subunits of 92 kDa. The enzyme showed maximum activity for the cleavage and synthesis of sucrose was at pH 7.0 and 8.0, respectively, and the optimum temperature was 40°C in both directions for HEPES-KOH buffer. The enzymatic reaction followed typical Michaelis–Menten kinetics, with the following parameters: Km (fructose),7.4; Km (UDP-glucose), 0.2612; Km (sucrose), 33.24; Km (UDP), 0.0946. The enzyme was very sensitive to inhibition by heavy metals.

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Marcelino Bazan Tene, Juan Manuel González Gonzalez, Francisco Radillo Juarez, and Pablo Enrique Ramírez Castillo

The tomato (Lycopersicon esculentum Mill.), is native to South America. It occupies the second place in worldwide vegetable consumption. Because of this, the evaluation of tomato varieties for the fresh consumption is important. The Mexican production is 1,908,607 tons of fresh product (SAGARPA, 2004). In the state of Colima, production has a mean efficiency of 18.13 t·ha-1 (INEGI, 2000). The following genotypes were evaluated `Peralta', `Montijo', Pavia', `Grande River', and `Yaqui' (control). A randomized experimental block was used, with five treatments and four repetitions. The obtained results indicate that `Yaqui' (control) had the better yield of fresh fruit, with 37.5 t·ha-1, followed by `Peralta' (27.2t·ha-1), and `Montijo' (12.6 t·ha-1), respectively. The height of plant in `Yaqui' was 68.8 cm and 60.26 cm in `Pavia'. In the days to flowering, after showing a homogenous behavior, pronouncing itself up to 27 days after the transplant; whereas the variety `Grande River' was pronounced up to 40 days. With respect to the number of total fruits by plant, a highly significant difference was observed. `Yaqui' produced 91 fruits, with `Pavia' and `Peralta' producing 50 and 37 fruits per plant, respectively. In conclusion, `Yaqui' was the genotype with greater yield and vigor.

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James Nienhuis, Julie Rodriguez, Wilber Phillips, Peter Hanson, and Liliway Engle

Worldwide, there are cuurently more than 60 germplasm banks that contain tomato (Lycopersicon esculentum) collections ranging is size from a few dozen to several thousands of accessions. In the utilization of these genetic resources sampling from only one germplasm bank may result in limiting available genetic diversity, whereas sampling from several germplasm banks may result in unnecessary redundancy. The current lack of knowledge regarding the relative magnitudes of genetic diversity contained within different collections makes it difficult to develop a core collection that maximizes genetic diversity. Two large tomato collections are housed at the Asian Vegetable Research and Development Center (AVRDC), Sanhua, Taiwan, R.O.C., and the Centro Agronomico Tropical de Investigacion y Enseoanza (CATIE), Turrialba, Costa Rica. Ninety-six accessions from CATIE and 102 accessions from AVRDC were randomly sampled from each base collection. The total of 198 accessions were charcterized for 103 polymorphic RAPD molecular marker bands. The results indicated that the two germplam banks sampled different genetic diversity. In addition, the magnitude of genetic diversity was greater in the AVRDC collection compared to CATIE.

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John R. Stommel and Kathleen G. Haynes

Anthracnose, caused by Colletotrichum coccodes, is a serious ripe tomato fruit rot disease. Genetic resistance to anthracnose is not available in commercial tomato cultivars, but has been reported in small-fruited Plant Introductions (P.I.), and with lesser intensity in a number of breeding lines. Transfer of high levels of resistance from these breeding lines or P.I.s to elite materials has proven difficult. Inheritance of resistance has been described as complex with at least six loci influencing resistance reactions. Segregating populations originating from a cross between a susceptible tomato breeding line and a large-fruited breeding line (88B147) with resistance derived from Lycopersicon esculentum var. cerasiforme P.I. 272636, were evaluated for anthracnose resistance. Analysis of anthracnose resistance in puncture-inoculated fruit indicated small, but significant, additive genetic effects for resistance. Additional populations were developed from crosses of a susceptible inbred processing tomato cultivar with: 1) the resistant P.I. 272636, 2) an unadapted small-fruited resistant line developed from P.I. 272636, and 3) the large-fruited breeding line 88B147, also with resistance derived from P.I. 272636. Small additive effects identified in large-fruited material, in comparison to the resistant P.I., suggests that resistance loci have been lost during germplasm development. This is consistent with the relatively larger lesions observed in large-fruited lines derived from P.I. 272636. Positive correlations were noted between small fruit size and high levels of anthracnose resistance. Identification of molecular markers linked to resistance genes in the respective populations will be discussed.

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Essaid Ait Barka, Siamak Kalantari, and Joseph Arul

Fresh fruit and vegetables are highly perishable because of their active metabolism during the postharvest phase. Previous studies showed that hormic dose of UV cause a delay in the senescence of tomato fruit by about 7 days. The objective of this study was to elucidate whether UV acts on the cell membrane in producing the phenomenon of delayed senescence, since it is known that UV radiation can provoke photooxidation of membrane lipids. Membrane lipid peroxidation was studied in tomato fruit (Lycopersicon esculentum Mill cv. Trust) treated by hormic UV dose, and was followed by assaying products of lipid oxidation during the storage period. We observed the production of lipofuscin-like compounds, malondialdehyde, aldehydes, pentane, ethane, and hydrogen peroxide within few days of the treatment. An increase in the efflux of electrolytes (total, potassium, and calcium) was also observed. An immediate increase in the level of these products of oxidation supports the hypothesis that UV radiation induces membrane lipid peroxidation. However, beyond 5 to 7 days after treatment, the production of oxidation products and electrolyte leakage were lower than the control fruits. Thereafter, the level of products of lipid oxidation associated with senescence was higher in control fruits than in treated ones. Results suggest that the initial oxidation stress by the exposure to UV led to biochemical reactions inducing the production of stress compounds, such as polyamines, which are non specific antioxidants. Consequently, a delay in the senescence was observed.

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Raymond Fung*, Chien Wang, David Smith, Kenneth Gross, Yang Tao, and Meisheng Tian

Methyl salicylate (MeSA) and Methyl jasmonate (MeJA) treatments increased chilling resistance of light red tomato (Lycopersicon esculentum cv. Beefsteak) and extended shelf life and fresh-cut quality. We previously showed induction of AOX expression by low temperature and that induction of AOX transcript by MeSA and MeJA is correlated with resistance against chilling injury in peppers. Here, we investigate tomato, which is genetically closely related to peppers and belongs to the same Solanaceae family. In particular, we used four EST tomato clones of AOX from the public database that belong to two distinctly related families, 1 and 2 defined in plants. Three clones designated as LeAOX1a, 1b and 1c and the fourth clone as LeAOX2. Probes for these four genes were designed and Southern blotting done to confirm that they do not cross-hybridize. We will present data from Southern, Northern hybridization and RT-PCR to show: (1) gene copy number of each of these AOX members in the tomato genome; (2) gene-specific expression profiles in response to MeSA and MeJA in cold stored tomato; and (3) the relative transcript abundance of these four AOX genes.

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Francisco Radillo-Juárez*

In the world horticultural production, the tomato (Lycopersicon esculentum Mill.) contributes with the 47% of the destined area. In Mexico, 10% of the area is cultivated under intensive systems, where is used one or more technologies for obtaining higher productivity and quality; however, the environmental conditions are determinant factors to produce red tomato in the dry tropic, influencing the adaptation and persistence in the market. The aim of this research was to evaluate the adaptation and yield performance of tomato hybrids in fresh production under mulching, fertilization and irrigation. The tomato cultivars used were: `Access', `Centurion', `Bishop', `Dean', and `Yaqui' (control). They were distributed under a Completely randomized blocks design with four replications. The experiment was carried out in Villa de Alvarez, Colima, México. `Yaqui' exhibited the highest plant height 98.8 cm, as web as the highest fruit diameter with 4.61 cm; `Bishop' produced the highest number with 154.5 fruits per plant, followed by `Yaqui', and `Centurion', with 91 fresh fruits. In the variable fruit weight, `Yaqui' showed 93.44 g. In total fresh fruit yield per plant, `Yaqui' produced the highest yield with 8.46 kg, followed by `Bishop' with 4.91 kg; and total yield of 117.5, and 68.2 t·ha-1, respectively. Yaqui' was the genotype with best adaptation and agronomic characteristics. We speculate that environment conditions in field are determinant factors in the introduction of new tomato introductions.