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C.B. Watkins, J.E. Manzano-Mendez, J.F. Nock, J. Zhang, and K.E. Maloney

The tolerances of strawberry fruit to postharvest CO2 treatments is an important factor in assessing their potential for extended storage and marketing, but little information on variation among cultivars is available. We have assessed differences in responses of seven strawberry cultivars (`Annapolis', `Earliglow', `Kent', `Honeoye', `Cavendish', `Jewel', and `Governor Simcoe') to high-CO2 atmospheres. Fruit were harvested at the orange or white tip stage of ripeness, kept in air, or 20% CO2 (in air), and sampled after 1, 2, or 7 days for analysis of firmness, color, and volatile concentrations. Berries from each cultivar were collected on three separate harvest dates. Flesh firmness measurements of all cultivars tested were higher when treated with high CO2, but the degree of firming was affected by cultivar and assessment time. For example, firmness of `Annapolis', `Earliglow', `Honeoye', and `Jewel' was consistently enhanced by CO2, compared with air, during storage. In contrast, firmness of `Kent' was not affected by treatment after 1 day of storage and benefits were relatively slight at each subsequent removal. Red color development of the fruits was affected by cultivar and treatment period, but not by CO2 treatment. Volatile accumulation varied greatly among cultivars. `Annapolis' for example, appears very tolerant of high-CO2 treatment levels as indicated by low accumulations of ethanol, acetaldehyde, and ethyl acetate in the fruit. In contrast, `Kent' and `Governor Simcoe' accumulated large amounts of these compounds. This study indicates that differences in cultivar responses to CO2 should be considered by growers planning to store fruit under these conditions to extend marketing options. Research supported in part by the North American Strawberry Growers Association.

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I. Kadzere*, C.B. Watkins, I. Merwin, F. Akinifessi, and J.D. Saka

Postharvest biology of Uapaca kirkiana, a native tree fruit to the miombo woodlands of some parts of Southern Africa, is little understood. Experiments have been carried out to determine the influence of pre-ripening storage treatments on subsequent fruit ripening characteristics. Mature but unripe fruit, collected from Dedza District in Malawi, were either held under ambient conditions, incubated in clay pots for 3 d or at 4 °C for 11 d. Fruit were removed from clay pots and cold storage, held under ambient conditions, and quality assessed daily. Color changed from green-yellow and/or brown-yellow in the unripe fruit to brown in ripe fruit. Low initial fruit compression was associated with hard and unripe fruit at harvest. Compared with both ambient and cold storage, incubating the fruits in clay pots resulted in advanced fruit softening as reflected by the high compression levels even on the day of removal from the clay pots. By day six after removal, compression had increased to a mean of 81 mm in the clay pot fruits while maximum levels were 56 and 38 mm for ambient and cold storage, respectively. Storing fruit at cold temperature delayed softening and deterioration compared with ambient and clay pot storage treatments. There was a general decrease in the total soluble solids content of the fruit during ripening, and was not influenced by the pre-ripening storage treatments. Decay increased during ripening for all the three treatments. Deterioration of the pulp in fruit, indicated by the development of a brown color and/or disintegration of the pulp, was observed with increasing time from removal. These results will be discussed in relation to the potential for improving storage of U. kirkiana.

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D.A. Rosenberger, J.R. Schupp, S.A. Hoying, L. Cheng, and C.B. Watkins

Control of bitter pit in `Honeycrisp' apples (Malus ×domestica) from trees treated during the growing season with foliar sprays of trifloxystrobin fungicide and calcium was evaluated in four replicated trials over 2 years. All trials were in commercial orchards of `Honeycrisp' trees that were 3 to 6 years old. The effectiveness of combining boron with foliar applications of calcium chloride (CaCl2) was evaluated in two trials, and effectiveness of harpin protein, used either alone or in alternating sprays with CaCl2 was assessed in one trial. Trifloxystrobin applied twice during the 30 days before harvest reduced bitter pit incidence at harvest in one of the four trials, but the reduction was transitory, no longer being evident when fruit were re-evaluated after 63 days of cold storage. Harpin protein did not affect disorder incidence. Calcium sprays failed to control bitter pit in treatments where the total elemental calcium applied was less than 2.7 lb/acre (3.03 kg·ha–1) per year for tree canopies that were sprayed to drip using 100 gal/acre (935.4 L·ha–1) of spray solution. In the two trials where some treatments involved application of at least 2.9 lb/acre (3.25 kg·ha–1) of elemental calcium per season, the incidence of fruit with bitter pit at harvest was reduced by 76% to 90%. Effectiveness of calcium sprays for bitter pit control was not enhanced by superimposing trifloxystrobin, boron, or harpin protein treatments. Flesh firmness at harvest was lower in calcium-treated than in non-treated fruit, and fruit maturity was more advanced on trees receiving boron sprays than on trees receiving no boron. In one trial, where the first calcium application was made approximately 2 weeks after petal fall and 4 days prior to a fruit thinning spray, crop load of trees that received calcium sprays, measured as number of fruit per cm2 trunk cross-sectional area, was 38% greater than on trees that received no calcium sprays. CaCl2 provided better control of bitter pit in `Honeycrisp' than any of the other materials tested.

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A.H.D. Francesconi, C.B. Watkins, A.N. Lakso, J.P. Nyrop, J. Barnard, and S.S. Denning

Fruit maturity, quality, calcium concentration and economic value of `Starkrimson Delicious' (Malus domestica Borkh.) apples, under a range of crop levels and European red mite [Panonychus ulmi (Koch)] cumulative mite-days (CMD), were best explained by local surface regression models involving CMD and crop load. Fruit from trees with low CMD and a light crop (125 fruit/tree, about 20 t/ha) were the most mature at harvest. Those fruit had higher ethylene concentrations, starch pattern indices, soluble solids concentrations, and watercore incidence at harvest than fruit from trees with low CMD and a normal crop (300 fruit/tree, about 40 t/ha), or with high CMD at any crop level. Those fruit also had higher incidences of watercore and internal breakdown after 4 months of cold storage. Calcium concentrations in fruit increased as crop load and CMD increased. Whole-canopy net CO2 exchange rate per fruit related better to fruit quality and calcium concentrations than either crop load or CMD alone, but was always a much worse predictor than local surface regressions. Low CMD and normally cropped trees had the highest crop value; lightly cropped trees had an intermediate crop value; while high CMD and normally cropped trees had the lowest crop economic value. Crop load should be considered when defining action thresholds for mites, and harvest schedules for apples should reflect crop load and mite populations on apple trees.