Search Results
Abstract
Seedlings of 11 genotypes of tomato (Lycopersicon esculentum, Mill.) were inoculated at the first true leaf stage with zoospores of Phytophthora parasitica under controlled conditions and evaluated for resistance based on seedling death. The same lines also were transplanted into two fields naturally infested with P. parasitica and grown to maturity. Disease severity in the field was evaluated based on plant death and canopy collapse prior to harvest. Resistance to P. parasitica was present in both commercial lines and accessions of L. esculentum var. cerasiforme (Dun.) A. Gray. Seedling resistance was generally a good predictor of resistance in mature plants. The relative resistance and susceptibility expressed in seedlings was reflected in 10 of 11 genotypes in the field. One cultivar that was susceptible in the seedling test appeared resistant in the field. Expression of resistance in both the seedling test and field was influenced by environmental factors.
Abstract
Soluble sugar and starch levels were measured in leaf, stem, and petiole tissues of 3 tomato (Lycopersicon esculentum Mill.) cultivars throughout plant development in order to 1) assess the contribution of reserve carbohydrates to final fruit yield and quality and 2) determine whether genotypic variation exists for this trait. In all 3 cultivars — ‘VF145B-7879’ (‘7879’), ‘UC82’ (‘82’), and ‘BL6807’ (‘6807’) — leaf tissue was found to accumulate high levels of both soluble sugars and starch. Stem and petiole tissues, although having high sugar content, accumulated little starch. An estimate of the proportion of fruit dry weight attributable to remobilization of nonstructural carbohydrate (NSC) from vine tissue was made by determining the dry weight of sugars and starch lost from vegetative tissue once the vine had ceased gaining weight and dividing by the final fruit dry weight. Values for ‘6807’ and ‘7879’ were 4.8% and 0.3%, respectively. No remobilization of NSC was apparent in ‘82’. The primary remobilized carbohydrate was leaf starch in both ‘6807’ and ‘7879’. Leaf and stem sugars were also remobilized in ‘6807’. The relatively high degree of remobilization in ‘6807’ was associated with early maturity and a high fruit/leaf ratio.
Abstract
Measurement of respiration rate and ethylene production at the climacteric of fruits of 4 tomato (Lycopersicon esculentum Mill.) cultivars and breeding lines—LA 1563 (1563), ‘VF145B-7879’ (‘7879’), ‘UC 134’ (‘134’), and R982 (982)—showed that fruits of ‘7879’ have lower rates of respiration and ethylene evolution than those of the other 3 genotypes. Analysis of progeny from a cross between 1563 and ‘7879’ suggested that a small number of genes with mostly additive effects control the difference in respiration rate between these 2 lines. A joint scaling test indicated that an additive-dominance model was adequate for analysis of the genetic variation. The number of effective factors was estimated to be 1.28 and the calculated narrow sense heritability was 0.49.
Abstract
Two tomato (Lycopersicon esculentum Mill.) genotypes, LA 1563, a high solids breeding line and ‘VF145B-7879’, an intermediate solids cultivar, were studied in an attempt to determine which morphological characteristics contribute to high solids content in the fruits, and to evaluate 1563 as genetic material for higher solids in processing tomato fruits. A genotypic difference in fruit solids was apparent from as early as 10 days after anthesis, and continued through fruit development. Between 10 and 50 days after anthesis, 1563 and ‘7879’ fruits increased in mean dry weight from 0.057 g to 5.16 g and from 0.101 g to 4.28 g, respectively. A growth analysis showed that lower harvest index, lower fruit yield and larger leaf area were associated with the higher solids of 1563, compared to 7879.
Eight tomato (Lycopersicon esculentum Mill.) genotypes were evaluated based on shoot dry weight for resistance to four isolates of Verticillium dahliae Kleb. race 2 in two greenhouse seedling experiments. The race 2 isolates, obtained from North Carolina, Brazil, and Spain, demonstrated no differences in pathogenicity on the eight lines tested, thus precluding the identification of a third V. dahliae race in this collection. However, highly significant differences in virulence were observed among the isolates. The Brazilian isolate was the most virulent. No tomato genotype showed resistance comparable to that conferred by the single dominant Ve gene to V. dahliae race 1. While all tomato lines were susceptible to all race 2 isolates tested, there were significant differences in susceptibility equal to differences in levels of resistance. IRAT L3, Morden Lac, Okitsu Sozai, and `UC82' significantly outperformed the lowest ranking line XXIV-a. `Earlypak 7', Morden Mel, and Philippine 2 performance was statistically indistinguishable from that of either the highest- or lowest-ranked lines. Genetic diversity in the host and pathogen and environmental conditions favoring the pathogen likely contributed to the genotype × isolate interactions observed in Expt. 1. These results suggest using diverse isolates when screening for improved race 2 resistance.
Abstract
Two parthenocarpic tomato (Lycopersicon esculentum Mill.) lines segregating for male sterility were grown in the field in three plantings. Male-fertile plants produced both seeded (showing more than five seeds when cut in half transversely) and low-seeded (showing 0-5 seeds) fruit, whereas male-sterile plants produced only parthenocarpic fruit. The objective of the experiment was to compare the compositional quality of seeded and low-seeded fruit from male-fertile plants with parthenocarpic fruit from male-sterile plants. Young fruit were thinned from male-fertile plants so that they would have fruit loads similar to the male-sterile plants. Parthenocarpic fruit were found to have higher percent soluble solids than low-seeded fruit, which, in turn, had higher values than seeded fruit. In general, parthenocarpic and low-seeded fruit had higher pH values than seeded fruit. Only seeded and parthenocarpic fruit were used to compare total solids, the ratio of water insoluble solids : total solids (WIS:TS), titratable acidity, and color. Parthenocarpic fruit, in general, had significantly higher total solids than seeded fruit. No consistent differences between fruit types were observed for WIS:TS ratio, titratable acidity, or color.
Abstract
Osmotic priming of seed was evaluated as a means of improving stand establishment, early seedling growth, and yield of processing tomatoes (Lycopersicon esculentum Mill. cvs. UC204 and 6203). Seeds were primed in aerated solutions of 3% KNO3 (w/v) or of polyethylene glycol 8000 (PEG) of equivalent osmotic potential (-1.25 MPa; 314 g-kg−1 of water) at 20°C for 7 days, rinsed, and dried in forced air at 30°. Under laboratory conditions, seeds primed in either osmoticum germinated more rapidly than untreated seeds at 20° and 30°. At 10°, the PEG treatment was of little benefit for either variety, while the KN03 treatment still reduced the time to 50% germination to 60% to 80% of the control value. Priming did not affect the final germination percentage. Seedling emergence in the field was evaluated in March and April planting dates. In both trials, seedlings from primed seeds emerged earlier and more uniformly than seedlings from untreated seeds. Seedlings from primed seeds maintained greater mean plant dry weights, leaf areas, and ground cover percentages than untreated seedlings throughout the preflowering period. This advantage was due entirely to early emergence rather than to an increased relative growth rate. The early growth advantage from seed priming did not improve earliness of maturity, total yield, or soluble solids content of fruit.
Abstract
Mobilization of carbohydrates to fruits of 2 genotypes of tomato (Lycopersicon esculentum Mill.) differing in total fruit solids content, LA 1563 (1563) and ‘VF145B-7879’ (‘7879’), was investigated. On the basis of 2 separate studies, fruits of 1563, the higher solids genotype, appeared to be stronger sinks for assimilates than fruits of ‘7879’. LA 1563 partitioned a significantly larger percentage of 14C to the fruits than ‘7879’. Fruits of 1563 took up more 14C-sucrose from agar medium than ‘7879’ fruits, both on the basis of total uptake and specific activity. Starch was found at higher levels in fruits of 1563 than in those of ‘7879’ from 10–30 days after anthesis. No starch was detectable in either genotype 50 days after anthesis. Fruit sucrose levels tended to be lower in 1563 than in ‘7879’ throughout fruit development. The possible physiological relationships between carbon metabolism and the rate of import of assimilates by fruits are discussed.