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Shiow Y. Wang and Miklos Faust

Ethylene biosynthesis and polyamine content were determined in normal and watercore-affected apple (Malus domestics Borkh. cv. Delicious). Fruit with watercore produced more ethylene and contained higher amounts of putrescine (PUT), spermidine (SPD), 1-aminocyclopropane-1-carboxylic acid (ACC), and 1-(malonylamino) cyclo-propane-1-carboxylic acid (MACC). The activities of ACC synthase and ethylene-forming enzyme (EFE) in watercore-affected fruit were also higher than in normal fruit. The EFE activity in severely affected flesh was inhibited, resulting in ACC accumulation and low ethylene production. S-adenosylmethionine (AdoMet) was maintained at a steady-state level even when C2 H4 and polyamides were actively synthesized in normal and affected fruit.

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Errol W. Hewett and Christopher B. Watkins

The incidence of external and internal bitter pit in `Cox's Orange Pippin' apple (Malus domestics Borkh.) fruit sprayed with normal therapeutic sprays either with or without Ca salts at 2-week intervals during the growing season was determined after 6 weeks of storage over 7 consecutive years. Following harvest, fruit was either vacuum-infiltrated with CaCI2 or received no further treatment. Although there was a tendency for fruit that had been sprayed and vacuum-infiltrated with Ca to exhibit the greatest degree of bitter pit control, this treatment was not significantly superior to Ca sprays alone. Vacuum infiltration alone reduced the disorder to a lesser extent than Ca sprays and was more effective in reducing external than internal bitter bit. The results suggest that Ca applications over the growing season are superior to postharvest vacuum-infiltration with Ca in the prevention of bitter pit.

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A.P. Medlicott, J.M.M. Sigrist, and O. Sy

The effects of harvest maturity of mangos (Mangifera indica L.) on storage tinder various low-temperature regimes and the influence of storage on quality development during subsequent ripening at higher temperatures were investigated. The capacity for storage of mango fruit depended on harvest maturity, storage temperature, and the time of harvest within the season. Development of peel and pulp color, soluble solids concentration, pH, and softening in `Amelie', `Tommy Atkins', and `Keitt' mangos occurred progressively during storage for up to 21 days at 12C. Based on the level of ripening change that occurred during 12C storage, immature fruit showed superior storage capacity than fruit harvested at more-advanced stages of physiological maturity. On transfer to ripening temperatures (25C); however, immature fruit failed to develop full ripeness characteristics. Mature and half-mature fruit underwent limited ripening during storage at 12C, the extent of which increased with progressive harvests during the season. Ripening changes during storage for 21 days were less at 8 and 10C than at 12C. Chilling injury, as indicated by inhibition of ripening, was found at all harvest stored at 8C, and in early season harvests stored at 10C. Fruit from mid- and late-season harvests stored better at 10 than at 12C, with no apparent signs of chilling injury. Flavor of mangos ripened after low-temperature storage was less acceptable than of those ripened immediately after harvest. Suggestions are made for maximizing storage potential by controlling harvest maturity and storage temperature for progressive harvests throughout the season.

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Jollanda Effendy, Don R. La Bonte, and Niranjan Baisakh

Skinning injury in sweetpotatoes (Ipomoea batatas) is responsible for significant postharvest loss resulting from storage diseases and weight loss. Unfortunately, there is no report on the genes involved in wound healing of sweetpotato and a better understanding will facilitate improved breeding strategies. An annealing control primer (ACP) system was used to identify genes expressed after skinning injury of sweetpotato cultivar LA 07-146 storage roots. Using 20 ACPs, 63 differentially expressed genes (DEGs) were identified. Functional annotation of the DEGs revealed that genes previously shown to respond to dehydration, those involved in wounding response, and the lignin and suberin biosynthesis pathways were induced in response to skinning. Expression analysis of 18 DEGs through quantitative reverse transcription–polymerase chain reaction (PCR) showed that DEGs involved in lignin and suberin pathways were up-regulated after 8 and 12 hours of skinning. Other genes showed up- or down-regulation in their transcript abundance depending on the time the storage root was sampled after intentional skinning. The genes up-regulated in response to skinning may be useful to identify expression markers for screening sweetpotato lines tolerant to skinning injury in breeding programs.

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Allan B. Woolf, Elspeth A. MacRae, Karen J. Spooner, and Robert J. Redgwell

Modifications to solubilized cell wall polyuronides of sweet persimmon (Diospyros kaki L. `Fuyu') were examined during development of chilling injury (CI) during storage and in response to heat treatments that alleviated CI. Storage at 0 °C caused the solubilization of a polyuronide fraction that possessed a higher average molecular mass than polyuronide solubilized during normal ripening. The viscosity of this fraction was 30-times that of normally ripened fruit. Fruit heat-treated before or following storage contained a soluble polyuronide fraction with a markedly lower average molecular mass and decreased viscosity than in chilling injured fruit. Heat treatment also impeded an increase in viscosity of the cell wall material if applied before storage. CI (gelling) was related to the release of polyuronide from the cell wall during storage and its lack of subsequent degradation. Heat treatments retarded polyuronide release but promoted degradation of solubilized polyuronides.

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Sylvia M. Blankenship and Edward C. Sisler

Scatchard plots for ethylene binding in apples (Malus domestica Borkh.), which were harvested weekly for 5 weeks to include the ethylene climacteric rise, showed C50 values (concentration of ethylene needed to occupy 50% of the ethylene binding sites) of 0.10, 0.11, 0.34, 0.40, and 0.57 μl ethylene/liter-1, respectively, for each of the 5 weeks. Higher ethylene concentrations were required to saturate the binding sites during the climacteric rise than at other times. Diffusion of 14C-ethylene from the binding sites was curvilinear and did not show any indication of multiple binding sites. Ethylene was not metabolized by apple tissue.

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Sylvia M. Blankenship and Michael D. Boyette

`Beauregard', `Jewel', `Hernandez', `Carolina Rose', and `White Delight' sweetpotato [Ipomoea batatas (L.) Lam.] roots were placed in chambers for curing at 30 °C and 50%, 70%, or 85% relative humidity (RH) for 1 week. Uncured roots were held at 15 °C and 90% RH. After curing, roots were removed temporarily from the chambers, and chamber conditions were reset for the following storage treatments: 15 °C/85% RH; 18 °C/70% RH; and 18 °C/50% RH. Roots were stored 3 to 4 weeks. Experiments were in factorial arrangements so all combinations of curing and storage conditions were present. Experiments were conducted in two seasons. Roots were subjected to a pressurized water jet and the amount of skinning that occurred was visually rated several times during curing and storage. Weight loss was measured in `Beauregard'. Susceptibility to skinning changed over time and with the temperature and humidity conditions. Curing at 30 °C and any humidity between 50% and 85% generally improved epidermal adhesion, but there were exceptions. Lower humidities promoted greater weight loss. Epidermal adhesion changed during storage, becoming both stronger and weaker, indicating that sweetpotato epidermis is in an active state even after curing. The standard curing and storage conditions of 30 °C/85% RH and 15 °C/85% RH, respectively, are still a reasonable practice.

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C. Fred Deneke, Kathleen B. Evensen, and Richard Craig

The postharvest quality of regal pelargoniums [Pelargonium × domesticum L. H. Bailey] is limited by petal abscission. Cultivars that have diverse postharvest longevities were selected to study ethylene sensitivity and endogenous ethylene production. Petals of both intact and detached inflorescences abscised in response to low dosages of exogenous ethylene (0.5 μl·liter-1 for 1 hour). Ethylene sensitivity varied among cultivars and increased with floret age. Silver thiosulfate reduced ethylene sensitivity and often extended floret longevity beyond that of the controls. A climacteric-like rise in endogenous ethylene production occurred in excised gynoecia (including the receptacle) as floret age increased from 1 to 12 days postanthesis. Ethylene production increased a few days earlier and achieved a higher maximum rate in `Parisienne' than in `Virginia'; `Parisienne' also abscised petals earlier. Relatively low levels of endogenous ethylene may regulate petal abscission, since inflorescences were very sensitive to exogenous ethylene, and increased endogenous ethylene production preceded petal abscission.

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O.L. Lau

Incidence of scald in nontreated and DPA (2000 mg·liter-1)-treated `Delicious' apples (Malus domestics Borkh.) was assessed after 8.5 months in 1.5% or 0.7% O 2 plus 1.5% CO2 at 0.2C, with and without C2H4 scrubbing. Incidence of scald was high in non-DPA fruit held in 1.5% O2, and DPA treatment reduced scald in fruit held in 1.5% or 0.7% O2. Scald control was better with 0.7% O2 and no DPA `treatment than with 1.5% O 2 and a DPA dip. Ethylene scrubbing had no effect on scald in fruit held in 0.7% or 1.5% 02. Susceptibility of fruit to scald-and flesh browning exhibited seasonal variation, which was related to the differences in fruit maturity and the amount of watercore at harvest, respectively. Chemical name used: diphenylamine (DPA).

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D. Gerasopoulos and D.G. Richardson

Pear trees (Pyrus communis L.), cv. d'Anjou, received foliar applications of X-77 surfactant and 32.3 mm CaCl2 at 55, 85, 125, and 137 days after full bloom (DAFB) and fruit were harvested at 147 DAFB. Samples of fruit were stored in air either at 20 °C continuously or at 5 or 10 °C for several periods, then transferred to 20 °C, to determine the effects of storage temperature and CaCl2 treatments on the development of the ethylene climacteric and flesh firmness loss. Control fruits held continuously at 20 °C required 70 days for the onset of climacteric ethylene production, which commenced when firmness had decreased to ≈20 N. Calcium-sprayed fruit required 80 days at 20 °C before the rise in ethylene and resisted softening for ≈50 days. Regardless of calcium treatment, pears stored at 5 or 10 °C required only 40 days to produce climacteric ethylene; fruit softening and internal ethylene concentration after storage at 10 °C were intermediate between those of fruits stored at 5 and 20 °C. Calcium application did not alter the sequence of ripening events.