Esculentum Cultivars Research Articles

SUGAR ACCUMULATION IN FRUIT OF CULTIVATED AND WILD SPECIES OF TOMATO

Sugar accumulation throughout fruit development in the cultivated tomato (Lycopersicon esculentum) and a wild green-fruited species (L. peruvianum) are being examined. Results obtained using HPLC demonstrate that the fruit of L. peruvianum accessions accumulate the disaccharide, sucrose, in addition to the monosaccharides, glucose and fructose, common to L. esculentum. When detectable, sucrose in the L. esculentum cultivar FM6203 was present at very low levels throughout development. Analysis of mature fruit of L. esculentum var. cerasiforme, L. pimpinellifolium, and L. cheesmanii accessions indicate glucose and fructose as the primary storage sugars. Similar to L. peruvianum, mature fruit of the green-fruited species, L. hirsutum f. typicum and L. hirsutum f. glabratum, accumulate sucrose in addition to glucose and fructose.

Variation in [75 Se]selenate uptake and partitioning among tomato cultivars and wild species.

Eight Lycopersicon esculentum cultivars and six wild taxa from four Lycopersicon species were tested for their ability to transport and distribute Se under low and high sulphate salinity conditions. Plants were exposed to [75 Se]selenate for 1 h. Significant variation was observed in both morphological and transport characteristics that control the short-term uptake and accumulation of selenate in tomato species. Among L. esculentum cultivars under low salinity, selenate uptake ranged from 126-184 pmol g f. wt root-1 h-1 and shoot 75 Se concentrations ranged from 40-66 pmol g f. wt shoot-1 . Shoot accumulation was affected by both specific root weight (SRW, root fresh weight/total plant fresh weight) and uptake of the cultivar. Distribution of tracer between root accumulation and transport to the shoot, expressed on a root weight basis, was similar in all cultivars. High sulphate salinity reduced uptake to around 22 pmol g f. wt root-1 h-1 in all cultivars and only small differences in shoot 75 Se concentration (7.4-10.5 pmol g f. wt shoot-1 ) were observed, indicating that root uptake rate was the primary determinant of shoot 75 Se concentration under these conditions. In the low-salinity treatment wild accessions showed a wider range of uptake rates (52-190 pmol g f. wt root-1 h-1 ) and shoot Se concentrations (12-79 pmol g f. wt shoot-1 ) than the cultivars. High sulphate salinity had a less inhibitory effect on Se uptake in the wild taxa than in the cultivars, with uptake rates of 18-63 pmol g f. wt root-1 h-1 and shoot concentrations of 7-28 pmol g f. wt shoot-1 measured. Differences in uptake, partitioning and SRW all contributed to the variation in shoot 75 Se uptake in these taxa at both salinity levels. One cultivar (UC82B) was tested under high chloride salinity. Uptake was reduced by 40% relative to the low salt control, compared with the 87% reduction observed under high sulphate salinity. The apparent inhibition in the presence of chloride salinity could be explained by the 40% reduction in selenate activity calculated for this solution relative to the control. Reduced selenate activity was insufficient to account entirely for the reduced uptake observed in this taxon under high sulphate salinity. In contrast, after allowing for reduced selenate activity, uptake by L. pennellii LA716 was little affected by an increase in sulphate from 2.9 and 38 mM, showing that considerable variation in selectivity of the transport system for selenate versus sulphate exists among Lycopersicon species.

Uniconazole controls growth and yield of greenhouse tomato

Tomato ( Lycopersicon esculentum cultivar ‘Summer Flavor’) seedlings received a single uniconazole soil drench at 0, 12.5, 25, 50, 100, 200 or 400 μg per plant at the five-leaf stage. After 2 weeks of growth, plant height, length and area of the fifth leaf, and plant fresh and dry weights progressively decreased with increasing rates of uniconazole. The rate of leaf production was unaffected at low rates of the retardant. Another group of seedlings received soil drenches at the above rates at the onset of flowering. Uniconazole applied at both stages resulted in short final plant height at all rates. Total fruit yield was reduced by uniconazole at the 12.5 μg per plant rate, with further reduction as rates increased. Yields of large fruits (≥ 110 g) increased at the two lower rates of uniconazole. The incidence of blossom-end rot (BER) was nearly eliminated by this retardant at all rates. Foliar application of uniconazole at the flowering stage with rates of 0, 25, 50, 100, 250, 500, 750 or 1000 μg per plant had less control on plant height compared with their respective rates as a soil drench. Total fruit yield was not affected until the rate exceeded 100 μg per plant. The incidence of BER decreased sharply with increasing rates of uniconazole. The number and weight of fruits ≥ 110 g were doubled at rates between 25 and 250 μg per plant. Plant fresh and dry weights were lower as a result of uniconazole foliar spray. Fruit number was reduced regardless of the rate and stage of uniconazole application.

A Chlorophyll Fluorescence Screening Test to Evaluate Chilling Tolerance in Tomato

The chilling tolerance of commercial Lycopersicon esculentum cultivars (H2653, H722), Solanum lycopersicoides, an F1 hybrid of S. lycopersicoides × Sub-Arctic Maxi, and 25 BC2F2 lines of L. hirsutum × H722 (backcrossed twice to H722) was evaluated using a chlorophyll fluorescence assay. The ratio of the initial to the peak fluorescence (Fo: Fp) measured from fully expanded leaves was chosen as an indicator of plant health. Chilling induced an increase in Fo: Fp that was correlated with the sensitivity of the plant to low-temperature stress. Values of Fo: Fp remained low for cold-treated S. lycopersicoides and the F1 hybrid, which showed few symptoms of chilling-related damage, whereas the commercial cultivars, which were essentially intolerant to low temperatures, had large increases in Fo: Fp. A full range of Fo: Fp values was measured in the 25 BC2F2 lines, indicating that some chilling tolerance from the L. hirsutum parent was expressed by plants in these populations.

Relationship Between Trichome Density in Tomato and Parasitism of Heliothis spp. (Lepidoptera: Noctuidae) Eggs by Trichogramma spp. (Hymenoptera: Trichogrammatidae)

During 1984 through 1986, eggs of Heliothis zea (Boddie) and H. virescens (F.) were collected from field-grown tomato accessions varying in levels of glandular trichome-based resistance to Manduca sexta (L.) (Lepidoptera: Sphingidae) and Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). Eggs were subsequently held in the laboratory to determine levels of egg parasitism, mortality, and hatch. Parasitism of eggs by Trichogramma petiosum Riley and T. exiguum (Pinto and Platner) was greatest on the Lycopersicon esculentum (Mill) cultivar susceptible to M. sexta and was lowest on all backcross lines ( L. esculentum × PI 134417) × PI 134417) and the highly resistant L. hirsutum f. glabratum C. H. Muller (PI 134417). Regression analyses indicated that trichome density accounted for the greatest proportion of variance in Trichogramma spp. parasitism of eggs. However, because the methyl ketones 2-tridecanone and 2-undecanone, which contribute to the insect resistance of PI 134417, occur in the glandular trichome tips, their effects on parasitism by Trichogramma could not be separated from the effects of trichome density in this study. Egg density, canopy volume, and number of stem terminals per plot were unrelated to the percentage of parasitism by the Trichogramma studied here.

Screening for Resistance to Tomato Fruitworm and Cabbage Looper among Tomato Accessions

Tomato fruitworm (Heliothis zea Boddie) and cabbage looper (Trichoplusia ni, Hübner) are two destructive insect pests of the cultivated tomato (Lycopersicon esculentum Mill.). The present investigation was conducted to screen wild (L. Hirsutum Hump and Bonpl., L. hirsutum f. glabratum Mull.) and cultivated tomato accessions for resistance to larvae of these insects, and to evaluate accession by environment (greenhouse vs. field grown plants), and by insect pest (polyphagous H. zea, vs. oligophagous T. ni) interactions for resistance. A petri dish bioassay technique was used, with larval survival on fresh foliage measured every 24 h over a 96‐h period. Mean number of larvae surviving 96 h was taken as a measure of susceptibility of an accession. Number of accessions screened for resistance to H. zea and T. ni were 38 and 33, respectively. Mean larval survival on L. esculentum cultivars ranged from 32 to 52% for H. zea and from 25 to 76% for T. ni. In contrast, six field and three greenhouse grown wild accessions had less than 10% survival of H. zea larvae after 96 h. With few exceptions, all wild accessions were resistant to T. ni, with few or no larvae surviving 96 h. More than 50% of larval mortality occurred in the first 24 h, suggesting the toxic action of phytochemicals as a likely mechanism of insect resistance. Accession by plant growth environment and accession by insect species interactions were both significant. In conclusion, resistance of tomato foliage to insect pest larvae was shown, using a petri dish bioassay procedure, to differ significantly with plant genotype, insect species, and the plant growth environment.

Identification of restriction fragment length polymorphisms linked to genes controlling soluble solids content in tomato fruit

Gene(s) conferring high soluble solids (SS) in tomato fruit had been backcrossed previously from a wild tomato species, Lycopersicon chmielewskii LA1028 (∼ 10% SS), into a L. esculentum cultivar, VF36 (∼ 5% SS), to derive a BC5S5 line, LA1563, similar to 'VF 36' but with 7-8% SS. DNAs from these lines and a tomato breeding line, H2038, were screened for restriction fragment length polymorphisms (RFLPs) using four restriction endonucleases and sixty clones chosen at random from a tomato cDNA library. Most of the cDNA clones (56) identified the same RFLP in 'VF 36' and LA1563 and a different RFLP in LA1028. However, two cDNA clones identified the same RFLP in LA1563 and LA1028 and a different RFLP in 'VF36'. To determine whether RFLPs identified by these two cDNA clones were linked to SS genes, a H2038 x LA1563 F2 population was screened for segregation of the RFLPs and for SS content. The segregation ratios of these RFLPs were consistent with ratios expected for codominant alleles at unlinked loci. Analysis of variance of SS content for different RFLP genotypic classes indicated that RFLP alleles at one of the loci were linked to genes controlling SS content. The RFLP allele from the high SS tomato line, LA1563, was associated with significantly higher SS content and, therefore, could be useful in selecting for high SS gene(s) in a tomato breeding program.

THE RESPONSE OF PEPPER AND TOMATO CULTIVARS TO CHALLENGE INOCULATION BY Peronospora tabacina

The host range of Peronospora tabacina, isolated in 1979, was investigated by inoculating seedlings of six pepper (Capsicum annuum) and 13 tomato (Lycopersicon esculentum) cultivars three times 14 days apart. Tomato cultivars were not infected whereas pepper cultivars Sweet Banana, Midway and Staddon’s Select were slightly infected after the second and/or third inoculation. Differences in host range of P. tabacina in various countries may be due to differences in genotypes of cultivars tested as well as in races of the pathogen.Key words: Pepper, tomato, tobacco, Peronspora tabacina, challenge innoculation, blue mold

A method for estimating K + and NO −3 uptake rate in hydroponics by a four-electrode conductivity sensor

A four-electrode conductivity sensor and associated electronics were designed and applied to the continuous monitoring of conductivity and the rate of K + and NO − 3 uptake in a hydroponic system. The new device was successfully used to monitor continuously the depletion rate of K + and NO − 3 in a hydroponic solution in which tomato plants ( Lycopersicon esculentum cultivar ‘Naama’) were cultivated. A model is proposed for estimating the rate of K + and NO − 3 uptake by the plant, and their total concentration, from conductivity measurements. Experimental results verify the proposed mathematical criterion for choosing the initial concentrations of K + and NO − 3, and validate the underlying assumption of the proposed model.

Low temperature seed germination of Lycopersicon species evaluated by survival analysis

Low temperature germination responses were evaluated for 18 high altitude accessions representing five wild Lycopersicon species and 19 accessions of L. esculentum which have reputed ability to germinate in the cold. Survival analysis indicated that one accession of L. chilense germinates better at 10°C than PI 120256, the fastest-germinating L. esculentum genotype, and that PI 120256 germinates as well as PI 126435 (L. peruvianum). Additional wild ecotypes exhibiting rapid germination at 10°C were identified from L. peruvianum and L. hirsutum. These ecotypes may possess genetic potential for introgressing cold germination ability into L. esculentum cultivars.

Survey of the Genus Lycopersicon for Variability in α-Tomatine Content1

Abstract Twenty-seven accessions from 6 species of the genus Lycopersicon and 1 accession of Solanum pennellii were surveyed for content of the glycoalkaloid, α-to-matine. Significant variation in alkaloid content was found to exist among the accessions. L. esculentum cultivars were found to contain much lower concentrations of α-tomatine than accessions of L. esculentum var. cerasiforme, L. pimpinellifolium, and the L. peruvianum accession, LA 462.

Plant Growth Conditions and Yield of Viable Protoplasts Isolated from Leaves of Lycopersicon esculentum and L. peruvianum

Protoplasts were isolated from leaves of the cultivated tomato Lycopersicon esculentum cultivar Rheinlands Ruhm and the wild species L. peruvianum which were grown under different environmental conditions. These conditions included different calcium concentrations in the root medium, treatment with abscisic acid and kinetin, and different temperatures and humidities. No consistent differences in final yields of protoplasts were found between control and plants treated with either calcium, abscisic acid or kinetin. The final yields, however, were significantly higher in plants grown under relatively high humidity (82 % relative humidity) and low temperature (15 °C) as compared with those grown under low humidity (56 %) and high temperature (25 °C). The increase of final yields was greater in the cultivated plants. Greater proportions of spherical as well as viable protoplasts as expressed by their plating efficiency, were isolated from plants grown under the lower temperature and higher humidity. Some of the changes characterize the leaves of plants grown under the different environmental conditions are discussed.

Amino Acid Uptake by Tomato Leaf Tissue Under Chilling Stress: Uptake Conditions and a Comparison of Lycopersicon Species of Different Chilling Resistance

Uptake of [3H]leucine by leaf fragments and roots from Lycopersicon esculentum (domestic tomato) and L. hirsutum (a wild tomato) was compared. Uptake of amino acids was affected by metabolic inhibitors and temperature. The L. esculentum cultivars studied, Rutgers and PI.341985, showed similar uptake rates above 12°C. After preincubation at the uptake temperatures below 12°C, the Q10 for uptake for PI.341985 was about 25 while for Rutgers it was about 125. The temperature response was similar for root and leaf material and for material grown at different temperatures (24/18 and 15/5°C). The temperature response of the uptake by leaf fragments of the wild races of L. hirsutum was related to the altitude of origin. The race from the highest altitude (3100 m) showed little change in slope in a plot of tog uptake rate versus temperature over the range 4-20°C. The race from the lowest altitude (30 m) resembled the cultivars of L. esculentum in its response to temperature and showed an increasing slope below 10°C. The race of L. hirsutum from 1500 m responded to temperature in an intermediate fashion. It is concluded that the decrease in the rate of uptake of amino acids during incubation at chilling temperatures can be related to genetic adaptation to the temperature of the native habitat and chilling resistance of the variety of Lycopersicon used.

Genotypic Responses to Salinity

Four ecotypes of the species Lycopersicon cheesmanii ssp. minor (Hook.) C.H. Mull. from the Galapagos Islands were compared with L. esculentum Mill cv. VF 36 with respect to salt tolerance. The L. cheesmanii ecotype that proved most salt-tolerant was selected for detailed comparison with the L. esculentum cultivar. Plants were grown in modified Hoagland solution salinized with synthetic seawater salt mix. Growth rates under saline conditions were examined and amino acid, sugar, total amino nitrogen, free acidity, and Na and K levels in the tissues of the most and least tolerant plants were measured under salt stress and nonstress conditions. Results indicate that all Galapagos ecotypes were far more salt-tolerant than was the esculentum cultivar. They could survive in full strength seawater nutrient solution while the esculentum cultivar could not in most cases withstand levels higher than 50% seawater. Growth rates were reduced in both species under saline conditions but the esculentum cultivar was more severely affected. High levels of total amino nitrogen, specific amino acids, and free acidity along with low sodium content were found in the salt stressed VF 36 cultivar. The opposite responses were noted in the salt stressed treatments of the Galapagos ecotype. Tissue sugar levels did not appear to be similarly correlated with salt stress in either species. Potassium content fell sharply during salinization in the Galapagos ecotype while in the esculentum cultivar it declined relatively little even at high levels of salinity.

High soluble-solids content in large-fruited tomato lines derived from a wild green-fruited species

An attempt was made to combine the high soluble-solids content of ripe fruits of the small, green-fruited Lycopersicon minutum with the horticulturally desirable characteristics of a standard L. esculentum cultivar. By backcrossing from the former to the latter, and by subsequent pedigree selection, pure-breeding lines in which soluble-solids content was elevated to 7-7.5 per cent—at least 2 percentage points above that of the recurrent parent—were synthesized. The new lines are comparable with the recurrent parent in size, color, and shape of fruit, plant habit, and yield, although they suffer from fruit softness, perishability, and other defects. The recombination of high soluble-solids content and large fruit size was achieved despite a moderately strong negative correlation (r = -0.46 in BC1) between these characters. Genetic linkages between soluble solids and a dominant delta-carotene character (possibly Del) as well as with the uniform ripening of unripe fruit (u) were also detected and broken by the backcross selection procedure. Additionally, soluble solids tended to be associated with several severe fruit-cracking defects. The continuous nature of distributions of soluble solids in the segregating generations, the linkage of solids content with several genetically independent characters, and the recapture of only part of the minutum genotype determining high soluble solids point to a complex, polygenic inheritance of this character. Several of the derived lines carry Ip, a dominant gene for intense fruit pigmentation evidently derived from L. minutum. A foliage variegation character of undetermined inheritance, and rv-4, a gene for reticulated virescence, also appeared de novo in the segregating generations, probably originating from mutation as deduced from genetic criteria. Appropriate genetic tests proved the existence of the r and y fruit pigmentation genes or similar alleles at the same loci in the minutum parent. The genetic difference between the parental species for certain fruit quality characteristics is thereby characterized.

Influence of light on peroxidase activity associated with resistance of tomato cultivars to Septoria lycopersici

Peroxidase activity in leaves of tomato, Lycopersicon esculentum Mill, cultivars Bounty, Campbell 1327, Heinz 1350, and Rutgar, infected by Septoria lycopersici Speg. and exposed to various intensities and wavelengths of light was assayed by means of acrylamide flat gel electrophoresis and 3-amino 9-ethyl carbazole stain. Under controlled environmental conditions noninoculated plants of the four cultivars showed similar peroxidase activity during 11 days. Inoculated plants of cultivars Bounty, Campbell 1327, Heinz 1350, and Rutgar, in order, showed increasing resistance to the early blight disease through increasing peroxidase activity in the host and decreasing numbers of lesions produced by the leaf spot pathogen. In decreasing light intensities the inoculated plants of the four cultivars showed increasing peroxidase activity and increasing resistance to the disease, with a notable exception occurring at a light intensity of 14 200 ergs/cm2 per second. When grown in various wavelengths of light the inoculated plants of the four cultivars also showed increasing peroxidase activity and increasing resistance to the disease, respectively, in green (515 nm), orange (640 nm), red (720 nm), yellow (546–550 nm), and blue (430–436 nm) light. The differences in the peroxidase activity per lesion between the control plants grown at 35 500 ergs/cm2 per second of white light and the inoculated plants grown in various decreasing light intensities and in various wavelengths of light were of a magnitude to be highly significant in the parasite–host interrelationship.