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  • Author or Editor: D.A. Huber x
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Bell pepper (Capsicum annum var. Jupiter) fruit were exposed to 1.5% O2 for 1 to 5 days at 20C to examine whether the low-O2-induced poststorage respiratory suppression (PRS) in whole fruit could be due to limitations in mitochondrial oxidative capacity. Mitochondrial oxidative capacity was not affected after storing bell peppers for 1 day in 1.5 % O2. Extending the storage period from 1 to 5 days in 1.5 % 0, resulted in PRS of CO2 production for about 55 hours after transfer to air, and a marked reduction in the oxidative capacity of isolated mitochondria. Mitochondrial activity was suppressed for 10 hours after transfer to air but, within 24 hours, bad recovered to values comparable to those of mitochondria from fruit stored continuously in air. Storing bell peppers in 1.5% O2 for 5 days resulted in a reduction in the respiratory control (RC), while ADP/O ratios were not affected. The reduction was temporary since the RC attained normal activity after returning bell peppers to air. Cyanide-sensitive cytochrome and CN-insensitive pathways were suppressed after storing fruit in 1.5 % O2 for 5 days. After returning fruit from a low-O2 atmosphere to air, the alternative pathway recovered at a greater rate than the cytochrome pathway.

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Abstract

Capsicum annuum (‘Early Calwonder’) seeds germinated (radicle protrusion) in 8 days at 15°C and 4 days at 25°. The seeds have an endosperm 7 to 9 cells in thickness which lies directly in front of the radicle. The external appearance of the endosperm did not change until one day before radicle emergence, when the endosperm in front of the radicle enlarged and protruded outward. This change was accompanied by breakdown and loss of endosperm cellular integrity and reduction in endosperm thickness directly in front of the radicle, but not in other regions of the endosperm. Gibberellic acid (GA4+7) decreased the time for appearance of the protruding endosperm and radicle protrusion through the seed coat by one day. Cell wall degrading activity was detectable during the early stages of germination and became extremely high after radicle emergence. Seeds treated with 100 ppm GA4+7 showed slightly increased enzyme activity during early germination and differences became more pronounced as germination progressed. Cellulase activity was not found in the extracts, but seed enzyme preparations degraded a galactomannan substrate. The enzyme exhibited only endohydrolytic activity, indicating an enzyme which may participate in the weakening of cell wall. It was postulated that an endomannanase is needed for endosperm breakdown in front of the radicle in order for rapid germination of pepper to occur. A reduction in germination temperature from 25° to 15° reduced the rate of radicle movement through the seed coat by one half.

Open Access

Analysis of a five-parent diallel in a greenhouse estimated general and specific combining ability (GCA and SCA) effects for resistance of Japanese plum (Prunus salicina Lindl. and hybrids) to Xanthomonas campestris pv. pruni (Smith) Dye stem canker, as measured by length of inoculated cankers, canker appearance rating, and canker expansion rate. `Friar' and `Gulfruby' were the most susceptible parents. `Burbank', `Wilson', and' Wade' had similar GCA values for length of inoculated cankers, but' Wade' was the superior parent in transmitting canker resistance, as measured by canker appearance rating. SCA was not important in determining the performance of a cross. Canker appearance rating was the best measure of resistance in the greenhouse tests and provided a greater separation of GCA estimates and lower coefficient of variation.

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Tree-ripe `Tommy Atkins' mangoes were not injured during storage in controlled atmospheres (CA) for 21 days at 8°C, and the fruit resumed ripening after transfer to air at 20°C (Bender et al., 1995). In our study, tree-ripe `Keitt' mangoes were stored at 5 and 8°C in either 10% or 25% CO2 combined with 5% O2 with control fruit maintained in air. Control fruit had higher percentages of electrolyte leakage than CO2-treated fruit at transfer from the CA and after 3 days in air at 20°C. Fruit stored in 25% CO2 at 5°C had significantly higher concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC), over 0.5 nmol ACC/g fresh weight in mesocarp tissue. All the other treatments had similar ACC levels (<0.3 nmol/g fresh weight) after 21 days in CA. Ethylene production rates at both temperatures were significantly lower in the 10% CO2 treatment than in control fruit and were not detectable in 25% CO2. Ethylene production was similar in all treatments after transfer to air. Fruit from the 25% CO2 treatment at 5°C developed dull, green-grayish spots on the epidermis, but otherwise epidermal color, as determined by chroma and hue angles, did not differ among the treatments. There also were no differences in flesh color and flesh firmness.

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Exposure to hypoxic O2 levels has been reported to result in better epidermal color, higher titratable acidity and soluble solids levels, delayed softening and reduced ethylene production and respiratory activity in many fruit species. Mangoes have been shown to tolerate short term (4 days) exposures to O2 concentrations below 0.5% with beneficial effects on firmness retention and maintenance of ground color. In the present work, `Haden' mangoes were stored for 14 days at 15°C with O2 levels ranging from 2% to 5% and compared to an air control and an atmosphere of 25% CO2 in air. `Tommy Atkins' mangoes were stored under the same treatments at 12°C for 21 days. After storage at 12 or 15°C the mangoes were transferred to air at 20°C for 5 days. Ethanol production rates during controlled atmosphere (CA) storage were significantly higher at O2 levels of 4% and below. Respiration (CO2 production) rates were reduced during CA storage but did not differ from the control after transfer to air. There were no differences in ethylene production as well as in flesh firmness, titratable acidity and total sugars. The ground color of mangoes kept under the lowest O2 concentration and under 25% CO2 was greener, as indicated by higher hue angles, than in the other treatments upon transfer to air at 20°C. However, only the mangoes stored under high CO2 maintained higher hue angles during the subsequent 5 days at 20°C.

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Two Guatemalan-West Indian avocado (Persea americana) hybrids (‘Monroe’ and ‘Booth 8’) were treated with an aqueous formulation of 1-methylcyclopropene (1-MCP) to determine effects on ripening and quality during storage simulating commercial shipping temperatures. Fruit harvested at preclimacteric stage were immersed in aqueous 1-MCP at 75 μg·L−1 (1.39 mmol·m−3) or in deionized water for 1 minute, stored at 10 °C for 14 days, and then transferred to 20 °C until ripe. Respiration rate, ethylene production, softening, and change in epidermal hue* angle were delayed and/or suppressed in both cultivars exposed to 1-MCP, although effects were less pronounced with Booth 8. Hue* angles for 1-MCP-treated ‘Monroe’ fruit had the highest values (darkest green peel color) of all treatments at full-ripe stage (hue* angle = 117). For control and treated ‘Monroe’ fruit respiration peaked on days 15 and 21, while ethylene production from both treatments peaked on day 16. Respiration and ethylene production peaked on day 16 for both control and 1-MCP–treated ‘Booth 8’ fruit. Fruit treated with 1-MCP consistently showed diminished respiration and ethylene peaks. Days to full-ripe stage were unaffected by treatment. ‘Booth 8’ fruit from both treatments were considered ripe (15 N whole fruit firmness) after 17 days; however, only 8% of control fruit were marketable, whereas 58% of 1-MCP-treated fruit were marketable, based on subjective appearance ratings using the Jenkins–Wehner score. The development of peel blemishes during storage was the primary cause of unmarketable fruit. ‘Monroe’ control and 1-MCP–treated fruit were soft after about 22 days and were significantly more marketable (control 70% and 1-MCP 85%). Avocados treated with 1-MCP ripened over a longer period than control fruit but maintained a higher percentage of marketable fruit.

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Fruit were harvested from an erect, thornless blackberry (Rubus L. subgenus Rubus Watson, `Navaho' to study ripening changes. Soluble solids content increased between the red (unripe) and dull-black (overripe) stages of ripening while titratable acidity decreased sharply between the mottled and shiny-black ripeness stages. Anthocyanin content increased sharply between the mottled and shiny-black stages. Firmness of drupelet and receptacle tissues decreased between the mottled and shiny-black stages of ripeness. In whole blackberries, total uronic acids decreased, and water soluble uronic acids increased between the green-red and shiny-black ripeness stages. Volatile production paralleled ripening changes, and was highest in dull-black fruit, with alcohols and aldehydes predominating. Respiration of intact fruit maintained in water decreased between the green and red ripeness stages and increased at the mottled (part-black) and black ripeness stages. Ethylene production remained below 10 nmol·kg-1·h-1 until the dull-black (overripe) stage of maturity. Free 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC oxidase did not increase in berries until the shiny-black stage, corresponding with the onset of detectable ethylene production. ACC oxidase activity decreased in the drupelet tissue (0.5 to 0.01 μmol·kg-1·h-1) and increased in the receptacle tissue (2 to 3.8 μmol·kg-1·h-1) as fruit changed from red to dull black. These results indicate that ripening in blackberries may be initiated in the receptacle tissue. Ripening in blackberries is likely independent of ethylene, but ethylene may regulate berry detachment from pedicels, thus controlling timing of fruit harvests.

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