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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.

Postharvest heat treatments were applied to three apple (Malus domestica Borkh.) cultivars: `Anna', `Golden Delicious', and `Jonathan'. The temperatures ranged from 38 to 50 °C and from 5 to 96 hours. The temperatures of 50 °C for 5 or 10 hours and 46 °C for 10 hours controlled all developmental stages of San Jose scale on `Golden Delicious' and `Jonathan' fruit. Blue mold germination was prevented by 46, 42, and 38 °C after 28, 34, and 42 hours, respectively. The time needed to control the fungus was longer than that required to kill the insect. Apples were damaged by a 50 °C treatment but could withstand at least 12 hours at 46 °C and at least 24 hours at 42 °C. At 38 °C no damage was found on preclimacteric apples even after 96 hours, but if postclimacteric fruit were heated at 38 °C heat damage occurred. The treatments that did not cause damage maintained the fruit firmness during post storage ripening. The results are discussed in the context of developing integrated postharvest heat treatments.

`Golden Delicious' apples (Malus domestica Borkh.) were treated after harvest with heat (air at 38 °C for 4 days or 42 °C for 1 day) or 2% CaCl2 (w/v; applied as a dip or pressure-infiltrated) or a combination of the two and stored at 0 °C for ≤6 months. Decay caused by Botrytis cinerea Pers.:Fr. after inoculation to a depth of 2 mm with a conidial suspension virtually was eliminated in stored fruit heated at 38 °C, regardless of Ca treatment. Apples punctured to a depth of 0.5 mm (but not 2 mm) and inoculated with B. cinerea on removal from storage were almost completely protected from poststorage decay if they had previously been pressure-infiltrated with 2% CaCl2, regardless of the heat regime. Heating fruit at 42 °C and dipping in 2% CaCl2 were only partially effective in preventing decay from either pre- or poststorage inoculations. Fruit firmness was not related to resistance to decay.

Commercial, ecological, and agrotechnical considerations have recently renewed interest in the use of physical rather than chemical means to maintain postharvest quality of horticultural crops. This review discusses prestorage heat treatments that protect against physiological disorders, enhance natural resistance to pathogen infection, reversibly inhibit fruit ripening, and permit flexibility in storage temperatures.

Apples (Malus domestica Borkh. cv. Anna) were treated at harvest by a dip in 3% CaCI2 solution, heated for 4 days at 38C, or the two treatments combined, before being placed in OC storage. After removal of the apples from storage and holding them for 1 week at 20C, the combined treatment maintained fruit quality best. The fruit remained firmer than with either treatment separately, and peel yellowing and decreased titratable acidity caused by the heat treatment were less pronounced. Heat treatment alone maintained fruit firmness, while CaCI2 alone had no effect on fruit quality, although it raised the fruit calcium level more than the combined treatment in most experiments. Altering the temperature (0, 20, or 38C) of the CaCl2 dip did not change its efficacy. There was less soluble and more insoluble pectin in cell wall extracts of apples from the combined treatment than from other treatments. In addition, proportionally less Ca was present in the water-soluble pectin fraction of the combined treatment compared to other treatments, indicating different binding properties in the cell wall.

Mature-green tomato (Lycopersicon esculentum Mill.) fruit, when kept for 3 days at 36, 38, or 40C before being kept at 2C for 3 weeks, did not develop chilling injury, while unheated fruit placed at 2C immediately after harvest did. When removed from 2 to 20C, the heated tomatoes had lower levels of K+ leakage and a higher phospholipid content than unheated fruit. Sterol levels were similar in heated and unheated fruit while malonaldehyde concentration was higher in heated fruit at transfer to 20C. The unheated tomatoes remained green, and brown areas developed under the peel; their rate of CO2 evolution was high and decreased sharply, while ethylene evolution was low and increased at 20C. In contrast, the heat-treated tomatoes ripened normally although more slowly than freshly harvested tomatoes: color developed normally, chlorophyll disappeared, and lycopene content increased, CO2, and ethylene evolution increased to a climacteric peak and K+ leakage increased with time. During prestorage heating, heat-stress ethylene production was inhibited, protein synthesis was depressed, and heat-shock proteins accumulated. There appears to be a relationship between the “heat shock response” and the protection of tomato fruit from low-temperature injury.

Anna' and 'Granny Smith' apples (Malus domestics Borkh.) that were held at 38C for 4 days before storage at 0C not only were firmer than controls upon removal from storage, but also softened more slowly during shelf life at 17C. Skin yellowing and loss of acidity attendant upon the heat treatment were not prevented by dipping fruit in 2% CaCl2 before heating. Both heat-treated and control fruit softened at the same rate upon exposure to ethylene at 100 µl·liter -1 upon removal from storage. The insoluble pectin content of cortical tissues was higher in heat-treated fruit than in controls after 10 days at 17C, while soluble pectin levels were lower. Arabinose and xylose levels were lower in cell walls from heat-treated cortical tissue, but the treatment had no effect on loss of galactose residues during shelf life. Previous researchers have noted that heating apples at 38C for 4 to 6 days after harvest retarded or inhibited fruit softening while maintaining most other aspects of storage quality (Liu, 1978; Porritt and Lidster, 1978). The exception was a slight yellowing of the skin and a decrease in titratable acidity in comparison with unheated fruit. Calcium treatments also extend the storage life of apples, primarily by reducing the rate of metabolic activity (Bangerth et al., 1972}, thus reducing senes- cence phenomena such as fruit softening, yellowing, and loss of acidity (Ferguson; 1984; Glenn et al., 1988). Since uptake of Ca by pear cells was specifically enhanced by heating cells at 38C (Klein and Ferguson, 1987), we endeavored to determine if heating Ca-treated apples could synergistically inhibit loss of fruit firmness in storage, without associated problems of acid loss and skin yellowing. The specific objectives of this research were to increase the effectiveness of postharvest Ca dips by use of a heat treatment, while simultaneously counteracting the disadvantages of heat treatment alone (loss of acidity and yellowing). Since heat treat- ment inhibits ethylene production by apples (Klein, 1989), we investigated whether softening could be reinduced by exposing heat-treated fruit to ethylene at 100 µl·liter -1 upon removal from storage. We also studied whether the decrease in apple fruit softening after a prestorage heat treatment is due to changes in the neutral sugar and pectin composition of the cell wall in cortical tissue.

Additional index words. Malus domestics, color, firmness, acidity, soluble solids concentration, ethylene, respiration Abstract. The benefits conferred by a prestorage heat treatment on poststorage quality of apples (Malus domestics Borkh.) were measured on 'Anna', a non-storing early cultivar, and 'Granny Smith', a long-storing late cultivar. The major benefit was a decrease in rate of apple softening, both during OC storage and during simulated shelf life at 20C. Soluble solids concentration was not affected by heat treatment, but titratable acidity was reduced. Ethylene production after heat treatment and storage was similar to or higher than that of control apples, but respiration was lower. The optimum temperature and time combination for prestorage treatment of both cultivars was 4 days at 38C. High temperatures have been reported to inhibit ripening of many-fruits "(Mitchell, 1986). If held for too long above 35C, fruit will fail to ripen normally when returned to lower temper- atures. However, pears and apples have been reported to ripen normally if held at 40C for up to 6 days and then returned to 20C (Maxie et al., 1974; Liu, 1978). Liu examined ripeness indices of four cultivars of apples after 2 or 4 days at 40C and found that, compared to control, the heat treatment lowered titratable acidity, retained firmness, and had no effect on soluble solids concentration (SSC). Porritt and Lidster (1978) reported similar changes after storage of heat-treated apples. We have examined this prestorage treatment on 'Anna' apples, a non- scoring early cultivar, and 'Granny Smith,' a long-storing late cultivar. We determined how long the effects persisted in stored apples by examining their rate of ripening, ethylene production, and respiration after various durations of storage. We also de

`Anna' and `Granny Smith' apples (Malus domestics Borkh.) that were kept at 46C for 12 hours or at 42C for 24 hours before storage at 0C were firmer at the end of storage and had a higher soluble solids: acid ratio and a lower incidence of superficial scald than unheated fruit. These heat regimes produced results similar to those obtained by keeping fruit at 38C for 72 or 96 hours before storage. Prestorage regimes of 46C for 24 hours or 42C for 48 hours resulted in fruit damage after storage.

Compounds that modulate the synthesis of gibberellin (GA) can also enhance resistance to abiotic stress in treated plants. Seed treatments of 600 ppm trinexapac-ethyl (TE), which inhibits GA synthesis by blocking the transformation of GA20 to GA1 and foliar applications of 15 ppm paclobutrazol (Paclo), which inhibits the oxidation of ent-kaurene to kaurenoic acid, were applied separately or together to three varieties of hot pepper (Capsicum annuum L.) that are popular in Thailand. Greenhouse-grown plants were subjected to 7-10 days of drought, and then rewatered before transfer to a screenhouse. Khee Noo (an upright “bird type” pepper) was most sensitive to drought, compared to Bang Chang and Hot (“cayenne type”). In all varieties, both Paclo and TE treatments reduced the height of irrigated plants, but led to the retention of both plant size and pepper yield in droughted plants, compared to either irrigated plants or to untreated droughted plants. Treatment with Paclo provided the greatest retention of leaf relative water content (RWC) under drought conditions, with no advantage to the combination Paclo+TE treatment. Only Paclo treatment increased leaf thickness in Bang Chan and Hot, whereas both Paclo and TE had similar effects on increasing leaf thickness in Khee Noo. Khee Noo was the variety most responsive to Paclo or TE treatments, with increases in leaf thickness, epicuticular wax, and leaf pigments, all of which may better allow the plants to survive stress by storing leaf moisture, enhancing photosynthesis (chlorophyll), and preventing oxidative injury (carotenoids). Electrolyte leakage, indicative of membrane permeability and thus of susceptibility to stress, was diminished by 25% to 33% in leaves from plants treated with Paclo or TE.

Apple (Malus domestica Borkh. `Grand Alexander') fruit were stored immediately at 0C after harvest or after being held at 38,42, or 46C for 72,24, or 12 h, respectively. Half of each fruit lot was dipped in 1.5 % CaCl before storage. Heating did not appreciably affect Ca uptake into epidermal or cortical tissue. Calcium and heat treatments acted synergistically in reducing the severity of superficial scald and in retaining fruit firmness after 5 months of storage, relative to nontreated or nonheated Ca-dipped fruit.

Prestorage heating of apples lead to enhanced retention of fruit firmness of as much as 10 N upon removal from storage, compared to unheated fruit. Further enhancement of firmness retention was obtained by dipping fruit in 2-3% calcium chloride after heating prior to storage. Cortical tissue of heated fruit had more insoluble and less water soluble pectin than unheated fruit, although the total pectin content was similar in both treatmenats. During the heat treatment neutral sugars were lost from the pectic fractions, with no accompanying decrease in galacturonic acid. No effect of heat treatment on degree of methyl esterification was observed in pectic fractions or in critical-dried whole tissues, using colorimetric and NMR techniques, respectively. Treatment differences in dissolution of the middle lamella were not observable in electron micrographs. We suggest that loss of neutral sugar side chains during the heat treatment may have lead to closer packing of the pectin strands and in turn hindered enzymatic cleavage during and after storage.

A prestorage heat treatment of 38C for 4 days applied to `Granny Smith' apples (Malus domestics Borkh.) before regular air storage at 0C inhibited the development of superficial scald. Heat-treated apples stored for 3 months had superficial scald levels similar to diphenylamine (DPA)-dipped apples, while all nontreated control apples had scald. After 5 or 6 months of storage, this inhibition of scald development by prestorage heat treatment declined. The prestorage heat treatment inhibited the accumulation of α-farnesene and conjugated trienes in apple cuticle during storage, while DPA inhibited only α-farnesene oxidation. This treatment may be a substitute for chemical treatments against scald not only for short-term storage of `Granny Smith' but possibly also for other scald-susceptible apple cultivars.

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).

Susceptibility of apples (Malus domestica Borkh. ‘Gala’ and ‘Granny Smith’) to impact damage increased from early to late harvest time and decreased during storage at 1°C. Impact damage was quantified as bruise depth, diameter, volume, or weight. Bruise weight calculated as a percentage of fruit weight was the least variable measurement of bruising that was also proportional to height to impact of the fruit. Although a range of 22 New Zealand-grown apple cultivars differed in susceptibility to bruising, the variation was not correlated with fruit density, fruit firmness, or polyphenol content and polyphenoloxidase (PPO) activity in epidermal and cortical fruit tissues.

A rapid sampling technique was developed to determine ethylene content of wood and buds of ‘Golden Delicious’ apple (Malus domestica Borkh.). The technique involves the use of a glass vial and 2 syringes per sample. One syringe was used to create a partial vacuum in a vial containing the sample tissue for a period of time, a second to remove a gas sample after the atmospheric pressure had returned to normal. On a n1/g basis, spur buds contained more ethylene than 1 or 2-year-old wood. Ethylene content of shoot bases remaining on the tree increased between 24 and 60 hours after pruning. Ethylene content of tissues sprayed with ethephon rose, then returned to normal after 9 days. The ethylene content of atmosphere in the Beltsville area fluctuated daily and should be considered in estimating absolute levels of ethylene generated by the tissue.

Detectable calcium accumulation of the tissue started at 10−3M of the bathing solution and increased with increasing concentrations thereafter. Calcium solutions of 10−3 to 10−1M were effective in inducing metabolic changes in tissue: they decreased respiration and increased protein synthesis. Much of the accumulated Ca (90%) could be exchanged from the tissue with Mg without changing the metabolic effect of the Ca. Although high concentration of Ca was needed to move metabolically active Ca into the site of its action, most of the Ca accumulated on exchange sites was metabolically inactive.