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X. Fan, L. Argenta, and J.P. Mattheis

'Elberta' peaches (Prunus persica L.) harvested 6 days apart were treated with 0.5 mL·L-1 1-MCP for 4 hours at 20 °C then stored at 0, 5, 10 or 20 °C. Fruit were ripened at 20 °C for 3 days after 1, 3, and 6 weeks of storage at 0, 5, and 10 °C. Treatment with 1-MCP delayed the onset of climacteric ethylene production and reduced respiration in fruit held at 20 °C. 1-MCP-treated fruit were firmer than untreated controls after storage at 0 or 5 °C. 1-MCP-treated fruit also had higher titratable acidity (TA) after 1 week of storage at 0 or 5 °C, but TA was lower compared to controls after 3 or 6 weeks of storage. Fruit stored at 5 °C had more severe internal browning, lower extractable juice and TA than fruit stored at either 0 or 10 °C, however, 1-MCP treated fruit had more severe internal browning than untreated fruit after 3 and 6 weeks of storage at 5 °C. Fruit from harvest 1 treated with 1-MCP and stored at 0 °C for 6 weeks failed to soften after removal from storage. Chemical name used: 1-methylcyclopropene (1-MCP).

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Björn H. Karlsson, Jiwan P. Palta, and Peter M. Crump

Our previous research has provided evidence that in-season calcium applications can increase tuber calcium and improve tuber quality with reduced internal defects. To determine if increasing the tuber calcium concentration also mitigates tuber bruise incidence, five commercially relevant potato (Solanum tuberosum L.) cultivars (`Russet Burbank', `Atlantic', `Snowden', `Superior', and `Dark Red Norland') were grown during three seasons, 1999–2001. Three split applications of a calcium/nitrogen water soluble blend totaling 168 kg·ha–1calcium were made starting at hilling. All plots, including controls, received an equal amount of total nitrogen in a season. Tubers were allowed to be bruised during normal machine harvest standard to commercial production in Wisconsin. Over 100 tubers from each replication (5–10 replications/treatment) were cut and examined for the incidences of bruise and internal brown spot. Paired samples of medullary tissue were taken for measuring calcium concentration. As expected, tuber tissue calcium concentration increased significantly, in all cultivars and in all years, with in-season calcium application. Bruise incidence varied among cultivars and seasons. Although tuber calcium concentration varied among seasons, `Atlantic' and 'Snowden' consistently had the lowest calcium concentration, whereas `Superior' and `Dark Red Norland' consistently had the highest calcium concentration. Meta-analysis of pooled data for three years showed that blackspot bruise incidence was significantly reduced with calcium application in `Atlantic', `Burbank', and `Snowden'. On the other hand, `Dark Red Norland' and `Superior' had low incidence of bruise and were unaffected by calcium applications. Regression analyses of pooled data from all cultivars for three years revealed a significant quadratic relationship between blackspot bruise and tuber tissue calcium as well as between blackspot bruise and internal brown spot. A linear to plateau plot of medullary calcium concentration versus blackspot bruise incidence revealed that bruise incidence is minimized between 200 and 250 μg/kg (dry wt)–1 tuber calcium concentration. To our knowledge, ours is the first study providing evidence for reducing bruise by improving tuber calcium. Variations in the bruise incidences among cultivars generally followed tuber calcium concentration suggesting a genetic control. Given the role of calcium in improved membrane health and enhanced wall structure, and as a modulator of physiological responses, it is not surprising that internal brown spot and bruise incidences are reduced by in-season application to calcium-deficient cultivars.

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Matthew D. Kleinhenz, Jiwan P. Palta, Christopher C. Gunter, and Keith A. Kelling

Three Ca sources and two application schedules were compared for their effectiveness for increasing tissue Ca concentrations in 170 to 284 g field-grown tubers of `Atlantic' potato (Solanum tuberosum L.). Additional observations were made of internal physiological defects. Paired measures of tissue (periderm and nonperiderm) Ca concentration and internal quality (±hollow heart, ±internal brown spot) were made on individual tubers produced in plots fertilized with N at 224 kg·ha-1 and Ca at either 0 or 168 kg·ha-1, supplied from either gypsum, calcium nitrate or NHIB (9N-0P-0K-11Ca, a commercial formulation of urea and CaCl2). Application of N and Ca at emergence and hilling (nonsplit) was compared to application at emergence, hilling, and 4 and 8 weeks after hilling (split). Tuber yield and grade were unaffected by treatments. Split Ca application (from either calcium nitrate or NHIB) increased mean tuber nonperiderm tissue Ca concentrations and the percentage of tubers with an elevated Ca concentration in both years compared with non-Ca-supplemented controls. Split Ca application also resulted in greater increases in Ca in nonperiderm tissue than nonsplit Ca application in 1994. Although the correlation coefficient between Ca level in periderm and nonperiderm tissue of >400 individual tubers was highly significant in both study years, linear regression analyses suggested the Ca level in the two tissues were poorly related. Split application was associated with a 37% reduction in the incidence of internal tuber defects, relative to nonsplit application in 1994. Calcium application did not affect tuber internal quality based on means analysis, but chi-square analysis suggested that Ca concentration and internal quality of individual tubers may be related. The incidence of internal defects was 16.4% in tubers with nonperiderm tissue Ca >100 μg·g-1 dry weight compared to 10.6% in tubers with nonperiderm tissue Ca >100 μg·g-1 dry weight. These data suggest that 1) it is feasible to increase tuber Ca levels by field applications of moderate amounts of Ca, 2) tuber quality is impacted by N and Ca application schedule, and 3) Ca concentrations in tuber periderm and nonperiderm tissues may be controlled independently.

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M. Bergevin, G.P. L'Heureux, and C. Willemot

Mature-green `Vedette' tomato (Lycopersicon esculentum Mill.) fruit were stored with (+P) or without (-P) peduncles at 1C. During storage and after return to ambient temperature, pigment content and electrolyte leakage of pericarp tissue and fruit internal atmosphere composition were monitored. The +P fruit showed severe chilling injury (CI) symptoms-shriveling and brown discoloration of the surface-on transfer to 20C after at least 8 days of exposure to low temperature. The chilling-injured fruit did not ripen normally; i.e., pigmentation did not change at 20C. The -P fruit were largely unaffected and ripened normally at 20C. Severely injured tomatoes showed an apparent decrease in electrolyte leakage after transfer to ambient temperature. The CO, content of the -P fruit internal atmosphere was significantly lower than in +P tomatoes after return to 20C. The peduncle scar has a greater permeability to gases than the skin and facilitates gas exchange with the external atmosphere. The accumulation of CO, in the internal atmosphere of the chilled +P fruit after transfer to 20C apparently promoted CI symptom development.

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Allan B. Woolf and Michael Lay-Yee

`Hass' avocados [Persea americana Mill.] were pretreated in water (38 °C for up to 120 min) immediately before 50 °C hot water treatments of up to 10 min. Fruit were stored for 1 week at 6 °C and ripened at 20 °C. External browning was evaluated immediately upon removal from cold storage, and fruit quality evaluated when fruit were ripe. Pretreatments at 38 °C tended to reduce the levels of external browning, skin hardening, and internal disorders, such as tissue breakdown and body rots, that were associated, and increased, with longer hot water treatments. A pretreatment of 60 min was the most effective for eliminating external browning, and reducing hardening of the skin when fruit were ripe following hot water treatment. Examination of heat shock protein (hsp) gene expression in avocado skin tissue, showed that levels of hspl7 and hsp70 homologous mRNA increased with increasing pretreatment duration. The results demonstrate that 38 °C pretreatments increase the tolerance of avocado fruit to subsequent hot water treatments.

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Senay Ozgen, Christopher Gunter, Bjorn Karlsson, and Jiwan Palta

Potato tuber tissue is calcium-deficient. Consequently, increasing Ca concentration is desirable to improve tuber quality. The purpose of the present study was to determine the influence of supplemental Ca and N fertilization on internal quality of potato. Three products (calcium nitrate, calcium chloride, and gypsum) were used to increase tuber calcium concentration. We tested combinations of both soluble sources of calcium and gypsum. Each treatment had five replications and received same total amount of N, supplied either from ammonium nitrate, liquid N (UAN: 50% urea + 50% ammonium nitrate) and calcium nitrate or combination of these sources (at rate of 225 kg·ha–1). The total Ca was applied at the rate of 168 kg·ha–1. Application of N at emergence and hilling (nonsplit) was compared to split application of N and Ca at hilling, 2, 4, and 6 weeks after hilling. At harvest, ≈100 tubers from each replication were cut in half along longitudinal axis and visually inspected for internal defect in both years. Application of Ca, especially in split schedule and from soluble sources, significantly increased tuber tissue Ca concentration. In 1998, the incidences of hollow heart (HH) and internal brown spots (IBS) were very low. The treatment containing calcium nitrate and calcium chloride combination produced the lowest total defects, whereas application of gypsum was not effective at reducing defects. In 1999, application of all Ca sources including gypsum, reduced HH and IBS. Data from these studies suggest that tuber calcium level is increased by field applications of moderate amount of Ca and tuber quality is impacted by N and Ca application. Furthermore, seasonal climatic variations appear to have dramatic influence on the incidence of internal defects in potato tubers.

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Michael Lay-Yee and Kellie J. Rose

`Fantasia' nectarine fruit [Prunus persica (L.) Batsch var. nectarina (Ait.) Maxim.], held at 0C for ≤ 1 week following harvest, were forced-air heated either immediately after removal from cold storage or after an overnight pretreatment at 20C. Fruit were heated to 41,43, or 46 ± lC for 24,36, or 48 hours. Following treatment, fruit were stored for 3 weeks at 0C, held at 20C for 1 or 5 days, and then assessed for quality. No significant damage, relative to nonheated controls, was observed in pretreated fruit subjected to 41C for 24 hours. Nonpretreated fruit given the same treatment showed only a slight increase in damage relative to controls. Higher temperatures and longer treatment times, however, were associated with an increased incidence of fruit damage (scald, internal browning, or decay). Heat treatment was associated with reduction in ethylene production and titratable acidity of the fruit following storage.

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Peter J. Hofman, Marcelle Jobin-Décor, and Janet Giles

The potential to use percentage of dry matter (DM) and/or oil of the flesh of `Hass' avocado as a maturity standard to determine the latest harvest for acceptable fruit quality, was investigated. `Hass' avocado fruit were harvested from early October to mid-January from a commercial orchard in subtropical Queensland. The percentage of DM and oil changed little during the harvest period, and the eating quality of the flesh remained high. However, the incidence of body rots (caused mainly by Colletotrichum sp.) and the flesh disorders grey pulp and vascular browning, increased with harvest. These results indicate that percentage of DM and oil are not reliable late-maturity standards because of the inconsistent change with later harvests, and that disease and internal disorders can be the main determinants of latest acceptable harvest, rather than eating quality.

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J.L. Smilanick, F. Mlikota, P.L. Hartsell, J.S. Muhareb, and N. Denis-Arrue

`Ruby Seedless', `Red Globe', and `Prima Red' table grapes were fumigated with the treatment schedule of the USDA-Animal Plant Health Inspection Service recommended for the control of mealybugs. Methyl bromide was applied at 64 g·m-3 (4.0 lb/1000 ft3) for 2 h at 16.1 to 18.3 °C (61 to 65 °F). The grapes were in commercial packages typical for each cultivar. After fumigation and 30 min of aeration, the grapes were stored 2 to 4 weeks at 5 °C (41 °F) and their quality assessed by evaluation of cluster rachis condition, shatter, berry cracking, decay, berry color, internal browning, bleaching injury, and firmness. None of the table grape quality parameters was significantly influenced by methyl bromide fumigation.

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S.B. Sterrett, M.R. Henningre, and G.S. Lee

Abbreviations: DAP, days after planting; IBS, internal brown spot; IHN, internal heat necrosis. 1 Associate Professor. 2 Professor. 3 Extension Horticulturist—Vegetables. Research supported in part by a grant from Anheuser Busch Co. We gratefully