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Rebecca S. Boone, Carl E. Sams, and William S. Conway

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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Muhammad S. Hadi, William S. Conway, and Carl E. Sams

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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George F. Kramer, Chien Yi Wang, and William S. Conway

Pressure infiltration of `Golden Delicious' and `McIntosh' apples (Malus domestica Borkh.) with polyamides resulted in an immediate increase in firmness. `Golden Delicious' apples were 2.7 N (0.25 mM spermidine) to 6.7 N (1.0 mM spermine) firmer, while `McIntosh' apples were 2.2 N (0.25 mM spermidine) to 5.3 N (1.0 mM spermine) firmer than the water-treated control. During 28 weeks of storage at 0C, the differences between the polyamine-treated and water-treated apples were even larger. Similar results were observed with a 3% Ca treatment, but the Ca treatment reduced the rate of softening to a greater extent than did the polyamine treatments in `Golden Delicious'. Polyamides increased the endogenous levels of the polyamides infiltrated; however, the levels declined rapidly with time in storage. Both polyamine and Ca inhibited the development of chilling injury symptoms (brown core) in `McIntosh'. The influence of polyamines on ethylene production was negligible in both cultivars. The Ca treatment, however, inhibited ethylene evolution in `Golden Delicious'. Polyamides, thus, may affect apple softening through rigidification of cell walls rather than through interactions with ethylene metabolism.

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Robert A. Saftner, William S. Conway, and Carl E. Sams

The effects of postharvest pressure infiltration of calcium chloride (CaCl2) solutions, fruit coatings and shrink-wrap film treatments of apples (Malus domestica Borkh. `Golden Delicious') on peel injury, quality attributes, respiration and internal atmospheres after storage at 0 °C for 2 to 6 months, and during subsequent ripening at 20 °C were investigated. CaCl2 treatments (0.14 to 0.34 mol·L-1) reduced internal and evolved ethylene and softening of fruits, but they also caused distinctive injury to the fruit surface. Following the CaCl2 treatments with a water rinse and a wax- or shellac-based coating or a shrink-wrap film reduced surface injury in fruits treated with 0.24 or 0.34 mol·L-1 solutions of CaCl2 and eliminated injury resulting from a 0.14 mol·L-1 CaCl2 treatment. The fruit coatings delayed ripening; as indicated by better retention of fresh mass, green peel color, titratable acidity and flesh firmness, and the reduced respiration and ethylene production rates that were observed upon transferring the fruits to 20 °C. Sequential treatments with CaCl2 and a shrink-wrap film also reduced fresh mass loss, respiration and ethylene production rates, but had no effect on other quality characteristics. Internal CO2 levels increased and O2 and ethylene levels decreased in surface coated fruits during storage at 0 °C. Coating fruits without the use of CaCl2 also delayed ripening though not as well as that for fruits sequentially treated with CaCl2 and a surface coating.

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Robert A. Saftner, William S. Conway, and Carl E. Sams

Three polyamine biosynthesis inhibitors, α-difluoromethylornithine (DFMO), α-difluoromethylarginine (DFMA), and α-methylornithine (MeOrn), alone and in combination with CaCl2, were tested for their ability to reduce in vitro growth and soft rot development in apple (Malus domestica Borkh.) fruit caused by Botrytis cinerea Pers.:Fr. and Penicillium expansum Link. All three inhibitors reduced the in vitro growth of the pathogens. Calcium had no effect on fungal growth in vitro. Pressure infiltration of millimolar concentrations of DFMO or DFMA or 25 g·L-1 CaCl2 solutions into apples reduced subsequent soft rot development by B. cinerea and P. expansum >40%. A combination treatment of Ca and DFMO or DFMA reduced decay >67%. Treatment of apples with MeOrn was less effective at inhibiting decay development. None of the inhibitors affected polyamine levels in apple cortical tissues. Some injury to the fruit surface was observed with Ca treatments. Fruit treated with Ca and any of the inhibitors were less firm than those treated with Ca alone. Specific polyamine biosynthesis inhibitors in combination with Ca may prove useful in reducing postharvest decay in apples.

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Bruce D. Whitaker, Joshua D. Klein, and William S. Conway

Postharvest heat treatment of apples maintains fruit firmness and reduces decay during storage. Four days at 38C are beneficial, but 1 or 2 days are detrimental. The cellular basis of these effects may involve changes in cell wall and membrane lipid metabolism. Lipids from hypodermal tissue of `Golden Delicious' apples were analyzed after 0, 1, 2, or 4 days at 38C. Major lipids included phospholipids (PL), free sterols (FS), steryl glycosides (SG), and cerebrosides (CB). Galactolipids (GL) were minor components. PL content fell ?10% after 1 day at 38C, was unchanged after 2 days, and began to rise again after 4 days. PL class composition did not change with heating, but fatty-acid unsaturation declined throughout. FS and CB content and composition changed little, whereas SG content cropped by ≈20% over 4 days. GL fell ≈50% during 1 day at 38C, with no change at days 2 or 4. A burst of PL catabolism followed by recovery of synthesis may in part explain the different effects of 1-, 2-, or 4-day heat treatments. GL loss (in plastids) may be related to the effect of heat on fruit color (yellowing).

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Robert A. Saftner, William S. Conway, and Carl E. Sams

Effects of postharvest pressure infiltration of distilled water, CaCl2 solutions at 0.14 or 0.27 mol·L-1 without and with subsequent fruit coating treatments of preclimacteric `Golden Delicious' [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. `Golden Delicious'] apples on volatile levels, respiration, ethylene production, and internal atmospheres after storage at 0 °C for 1 to 6 months, and during subsequent shelf life at 20 °C were investigated. Over 30 volatiles were detected, most of the identified volatiles were esters; the rest were alcohols, aldehydes, ethers, a ketone, and a sesquiterpene. Pressure infiltration of water and increasing concentrations of CaCl2 resulted progressively in reduced total volatile levels, respiration, ethylene production, and internal O2 levels and increased CO2 levels in fruit following 2 to 4 months storage in air at 0 °C. Total volatile levels, respiration, ethylene production, and internal atmospheres of CaCl2-treated apples at 0.14 mol·L-1 gradually recovered to nontreated control levels following 2 weeks of shelf life at 20 °C and/or storage at 0 °C in air for more than 4 months. Following the calcium treatments with a shellac- or wax-based coating had similar but stronger and more persistent effects on volatile levels, respiration, ethylene production, and internal atmospheres than those found in fruit treated with CaCl2 alone. Calcium infiltration did not change the composition of volatile compounds found in fruit. Results suggest that pressure infiltration of `Golden Delicious' apples with CaCl2 solutions transiently inhibited volatile levels, respiration, and ethylene production, in part, by forming a more-or-less transient barrier to CO2 and O2 exchange between the fruit tissue and the surrounding atmosphere.

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Robert A. Saftner, William S. Conway, and Carl E. Sams

Changes in tissue water relations, cell wall calcium (Ca) levels and physical properties of Ca-treated and untreated `Golden Delicious' apples (Malus×domestica Borkh.) were monitored for up to 8 months after harvest. Pressure infiltration of fruit with CaCl2 solutions at concentrations up to 0.34 mol·L-1 reduced both fruit softening and air space volume of fruit in a concentration-dependent manner. Turgor potential-related stress within the fruit persisted during storage and was higher in Ca-treated than in untreated fruit. Fruit that were pressure infiltrated with CaCl2 solutions between 0.14 and 0.20 mol·L-1 and then waxed to reduce water loss during storage showed no peel injury. Calcium efflux patterns from apple tissue disks indicated two distinct Ca compartments having efflux kinetics consistent with those for cell wall Donnan-phase bound and water free space soluble Ca. At Ca concentrations up to 0.20 mol·L-1, cell wall bound Ca approached saturation whereas soluble Ca showed a linear dependence. At higher external Ca concentrations, only soluble Ca in the tissue increased. During 8 months of cold storage, cell wall Ca-binding capacity increased up to 48%. The osmotic potential of apples harvested over three seasons ranged between-1.32 and -2.33 MPa. In tissue disks, turgor potential changes caused by adjusting the osmolality of the incubation solution with CaCl2 or sorbitol were accompanied by changes in the osmotic and water potentials of the tissue. In CaCl2 solutions up to 0.34 mol·L-1, turgor potential was ≥0.6 MPa in tissue incubated in 0.14 or 0.17 mol·L-1 solutions of CaCl2 and was more than 3 times higher than in tissues incubated in low (≤0.03 mol·L-1) or high (≥0.27 mol·L-1) concentrations of CaCl2. At osmotically equivalent concentrations, turgor potential was up to 40% higher in Ca-than in sorbitol-treated tissue. The results suggest that postharvest treatment with 0.14 to 0.20 mol·L-1 solutions of CaCl2 are best for maintaining fruit water relations and storage life of `Golden Delicious' apples while minimizing the risk of salt-related injuries to the fruit. While higher concentrations of CaCl2 may better maintain firmness, these treatments adversely affect fruit water relations and increase the risk of fruit injury.

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W. Robert Trentham, Carl E. Sams, and William S. Conway

Mature apples (Malus domestica Borkh. cv. Golden Delicious) were immersed for 2 min in 0, 0.14, 0.27, or 0.41 mol·L−1 (0, 2%, 4%, or 6%, respectively) aqueous solutions (w/v) of CaCl2 at 0 or 68.95 kPa, and were stored at 0 °C. Histological samples of peel/cortex were taken at harvest and at four monthly intervals in storage. Paraffin sections were stained with an aqueous mixture of alcian blue 8GX, safaranin 0 and Bismark brown Y, or with the periodic acid-Schiff (PAS) reaction. No histological difference was observed in fruit treated with 2% CaCl2 compared with those pressure-infiltrated with greater amounts of Ca. Fruits pressure-infiltrated with 6% CaCl2 exhibited the greatest amount of flattened epidermal cells and hypodermal cavities. Cuticles were also affected at the higher CaCl2 treatment levels (with regard to staining with Bismark brown), becoming more condensed and uniform. Cuticle and hypodermis were stained differentially with PAS in the 6% CaCl2 treatment. All tissues, including the cuticle, were stained magenta red, indicating a possible chemical alteration of the cuticle and the underlying tissue by Ca.