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  • Author or Editor: William S. Conway x
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Calcium has been linked to disease resistance in fruits and vegetables. The effects of calcium nutrition on six hydroponically grown tomato cultivars (`Switch', `Match', `Blitz', `Caruso', `Trust', and `Celebrity') were evaluated in the fall of 1996. Disease resistance and yield were measured for plants grown in either perlite or pine bark mulch. Plants were fertilized with a 5N–11P–26K water-soluble fertilizer solution containing micronutrients and either 60, 120, or 185 mg·L–1 calcium. Disease resistance was determined by measuring disease lesion diameters on mature green harvested fruit 3 to 5 days after inoculating with Botrytis cinerea Pers.: Fr. There was no significant difference in disease when evaluated by medium, cultivar, or calcium treatment. Foliar analysis by Inductively Coupled Argon Plasma Atomic Emission Spectrophotometer (ICAP) indicated that leaf calcium content ranged from 27,000 to 54,000 μg·g–1 dry weight (leaf above fifth flower cluster), but was not significantly different when analyzed by medium, cultivar, or calcium treatment. There was no significant difference in marketable yield due to medium or calcium treatment. Among cultivars, `Trust' had the highest marketable yield at 2.7 kg per plant, which was significantly different from `Celebrity' at 1.6 kg per plant. This experiment suggests that a cheaper medium (pine bark) and lower calcium levels can be utilized in fall tomato production.

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An experiment was conducted to investigate the effect of Ca nutrition on yield and incidence of blossom-end rot (BER) in tomato. Three levels of Ca (low = 20 ppm, medium = 200 ppm, and high = 1,000 ppm; selected to represent very deficient, normal, and very high levels of calcium) were applied to three cultivars of tomatoes (`Mountain Supreme', `Celebrity', and `Sunrise'; selected to represent genetic differences in susceptibility to BER) grown in modified Hoagland solutions using a greenhouse hydroponic system. The experiment was constructed in a randomized complete-block design with three blocks, two replications, three cultivars, and three calcium treatments. The source of basic nutrients was a 5–11–26 soluble fertilizer containing micronutrients. The ratio of N–P–K was adjusted to 1.0–1.3–3.0 by adding NH4NO3 (34% N). Calcium was added as CaCl2. Nitrogen concentrations were maintained at 30 (first month), 60 (second month), and 90 ppm (during fruit growth), while the concentration of other nutrients followed proportionally. Cultivars differed significantly in yield and average fruit weight but not in incidence of BER or leaf Ca concentration. There was no cultiva × calcium treatment interaction. Leaf Ca content across cultivars was increased by 34% and 44%, respectively, by the medium and high Ca treatments. Average fruit weight and total yield per plant were not significantly different between the low and medium Ca treatments, however, both were reduced by the high Ca treatment. Incidence of BER was 95% higher in the low rather than in the medium Ca treatment. There was no significant difference in BER between the medium and high Ca treatments.

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`Golden Delicious' apples were pressure-infiltrated (34 kPa) at harvest with 0, 20, 35, or 50 g·L–1 solutions of CaCl2 followed without and with a water rinse, a wax or shellac emulsion treatment, or a shrink-wrap packaging, and stored at 0°C. The CaCl2 treatments delayed senescent breakdown, but also caused superficial injury to the fruit. A water rinse in combination with a wax- or shellac-based coating or shrink wrap packaging reduced the appearance of superficial injury in fruit treated with 35 or 50 g·L–1 solutions of CaCl2 and eliminated it in fruit treated with a 20 g·L–1 solution of CaCl2. While reducing the risk of calcium-related injury to the fruit, the coating and film treatments maintained the beneficial effects of calcium on apples and reduced weight loss of the fruit during cold storage.

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Due to the declining availability of fungicides for use in commercial tomato production, there is a need to investigate alternative disease control methods. Several theories of disease resistance are associated with an increase in plant tissue calcium content, which has increased resistance of tomato seedlings to bacterial wilt and other diseases. Three tomato cultivars (`Mountain Supreme', `Sunrise', and `Celebrity') were grown in a greenhouse hydroponic system to study the role of Ca in reducing decay of fruit by Botrytis cinerea. Calcium treatments of 20, 200, or 1000 ppm were applied in a modified Hoagland's solution. A 3 × 3 factorial randomized complete-block design was used. Mature whole leaves were collected from immediately below the third flower clusters and the calcium content analyzed by inductively coupled plasma emission spectrophotometry. Harvested fruit were inoculated with a 5 × 105 spore/ml conidial suspension of B. cinerea and the decay lesion diameter measured once daily for 7 days. This was repeated for 8 consecutive weeks. Leaf Ca content significantly increased (P < 0.01) as the Ca treatments increased from low to medium (310%) and from medium to high (150%). The medium and high Ca treatments significantly reduced the area of decay caused by gray mold rot (P < 0.01). There were no differences in Ca content or decay among cultivars, and the Ca × cultivar interaction was not significant. It appears that leaf Ca content is negatively associated with resistance of greenhouse-grown tomatoes to gray mold rot, strengthening the hypothesized role of calcium in promoting disease resistance.

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Fruit from five apple (Malus domestica Borkh.) cultivars were pressure-infiltrated at 103 kPa for 6 min with a 0%, 0.73%, 1.46%, 2.91%, or 5.82% (w/v) Ca-equivalent solution of CaCl2, Ca EDTA chelate, or buffered CaCl2 solution (Stopit). The fruit were stored at 0 ± 1C for 18 weeks and then evaluated for Ca content, firmness, and injury. Fruit treated with Ca chelate had no increase in fruit Ca content and were injured at all treatment levels. No significant differences occurred in fruit Ca levels between CaCl2 and Stopit treatments across all cultivars tested. Apples treated with Stopit were firmer than apples treated with CaCl2, when averaged across cultivars. Fruit Ca levels, firmness, and incidence of injury were positively correlated with concentrations of CaCl2 and Stopit for all cultivars.

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Frozen hydrated buds and epicarp of `Golden Delicious' apple (Malus domestica Borkh.) were observed with a low-temperature, field emission scanning electron microscope (SEM). In addition to observing surface features of these specimens, holders were modified to observe fractured specimens. A modified hinged holder retained both halves of a fractured specimen for examination of the complementary faces of frozen hydrated tissues. Low-temperature SEM avoided artifacts, such as extraction, solubilization, and shrinkage, which are normally encountered with chemical fixation, dehydration, and drying, respectively. The technique allowed observations of well-preserved frozen hydrated structures, such as the platelets of epicuticular wax; loosely associated organisms on plant surfaces, such as spider-mite eggs; delicate structures, such as fungal hyphae; and partially hydrated tissues, such as fruit epicarp and winter bud scales.

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`Golden Delicious' and `Red Rome' apples were pressure infiltrated (69 kPa for 2 or 4 min) at harvest with 0, 1, 2, 3 or 4%, and 0, 2, 4, 6 or 8% CaCl2 solutions (w/v), respectively, and placed in 0°C storage. Juice was extracted from the apples after 0, 2, 4 or 6 months in storage. Sensory evaluation of the juice was conducted to determine if CaCl2 concentration affected color, off-flavors, suspended particles or overall acceptability of the juice. Juice color was judged lighter with increased CaCl2 in both cultivars. Detection of off-flavors decreased as CaCl2 was increased in juice from `Red Rome'; whereas, off-flavors increased as CaCl2 was increased in `Golden Delicious' juice. CaCl2 treatments decreased suspended particles in both cultivars. As CaCl2 was increased overall acceptability of juice from `Red Rome' increased, while acceptability of juice from `Golden Delicious' decreased.

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The viability of Penicillium expansum Link conidia in sporulating culture declined rapidly when exposed to 38 °C, and when conidia were exposed to 38 °C prior to inoculation of apple fruits (Malus ×domestica Borkh.), the resulting lesions were smaller than those on fruit inoculated with nonheated conidia. `Gala' apples were heated after harvest (38 °C for 4 days), pressure infiltrated with a 2% solution of CaCl2, or treated with the antagonist Pseudomonas syringae van Hall, alone or in combinations to reduce postharvest decay caused by Penicillium expansum. After up to 6 months in storage at 1 °C, no decay lesions developed on fruit that were heated after inoculation with P. expansum, or any combination of P. expansum, antagonist, or Ca. Parallel lots of heat-treated and nonheated fruit that were either infiltrated or not infiltrated with Ca were stored up to 6 months. They were then inoculated with P. expansum alone, or with the antagonist followed by P. expansum. Prior heat treatment did not influence lesion size. Calcium alone, the antagonist alone, and heat plus Ca all reduced the incidence of decay by ≈25%, whereas heat plus the antagonist reduced it by 70%. Calcium plus the antagonist or Ca plus the antagonist and heat reduced decay incidence by 89% and 91%, respectively. The integrated strategy of heat-treating fruit, followed by Ca infiltration and then treatment with an antagonist, may be a useful alternative to controlling postharvest decay with fungicides.

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Air heat, methyl jasmonate dip, and vapor treatments with the ethylene action inhibitor 1-methylcyclopropene (MCP) were used to evaluate their effects on ripening-related characteristics and susceptibility to fungal decay in `Golden Delicious' apples (Malus ×domestica Borkh.) through 5 months of storage at 0 °C and ripening at 20 °C for 7 days. Preclimacteric fruit were treated with MCP vapor at a concentration of 1 μL•L-1 for 18 h at 20 °C, 38 °C air for 4 days, methyl jasmonate dip at concentrations of 10-5 and 10-4 for 3 min at 20 °C, combinations thereof, or left untreated before storage in air at 0 °C. One set of untreated fruit was stored in a controlled atmosphere of 1.5 O2 and 2.5% CO2 at 0 °C. The MCP treatment and CA storage delayed ripening, as indicated by better retention of green peel color and flesh firmness, and the reduced respiration, ethylene production rates, and volatile (both flavor- and superficial scald-associated) levels that were observed upon transferring the fruit to 20 °C. The MCP treatment followed by air storage delayed ripening more than CA storage. The heat treatment also delayed ripening but hastened skin yellowing. While methyl jasmonate dips had no significant effect on ripening, they were the only treatments used that reduced the incidence of postharvest decay and discolored the surface of some fruit. The results indicate that MCP may provide an effective alternative to CA for maintaining quality during cold storage and ripening. The results also indicate that methyl jasmonate dip treatment may reduce postharvest decay of fruit while maintaining fruit quality.

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