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Ethylene induces postharvest problems in many fruits, including members of the Cucurbitaceae. The effects of ethylene and its antagonist 1-methylcyclopropene (1-MCP) were studied on cucumber fruit, a cucurbit harvested immature. Beit Alpha cucumbers (cv. Manar) were harvested and exposed to 0.5 or 1.0 μL·L-1 1-MCP prior to exposure to ethylene at 10 μL·L-1 at 15 °C. Fruit exposed to ethylene exhibited significant quality loss upon exposure to ethylene, including epidermal yellowing, a 40% reduction in firmness and, following longer exposure (6 d), epidermal sloughing and placental watersoaking. After 8 d, cucumbers exhibited a 75% reduction in firmness and acute pathogen incidence. Control fruit (no ethylene, no 1-MCP) were visually acceptable but firmness had declined 30% compared with initial values. Fruit exposed to 1-MCP were resistant to applied ethylene, with firmness declining 10 (1.0 μL·L-1 1-MCP) to 20% (0.5 μL·L-1) during storage for 14 d at 15 °C. Firmness of fruit treated with 1-MCP at 1.0 μL·L-1 was 28% higher than controls receiving only air, suggesting that ethylene production contributes to softening of cucumber during storage. The softening and watersoaking of fruit treated with ethylene was accompanied by downshifts in pectin mol mass. Fruit exposed to 1-MCP showed significantly reduced mol mass downshifts. The data indicate that cucumber show a PCD response to ethylene that is largely prevented by suppression of ethylene perception. The response of cucumber to ethylene parallels that for other cucurbits, and provides additional information that the benefits of 1-MCP extend beyond application to climacteric fruits.
The present study was conducted to explore the process of watersoaking seen previously in beit alpha-type cucumber fruit treated with ethylene. Fruit were harvested at four levels of maturity: Immature (4 to 8 days after anthesis, DAA), Mature (10 to 14 DAA), Breaker (16 to 20 DAA), and Yellow (35 to 40 DAA). Fruit were then stored at 13 °C in the presence of air (control) or either 10 μL·L-1 ethylene or 1300 μL·L-1 propylene for up to 12 days. The physiological response to ethylene treatment varied with fruit maturity. Immature-stage fruit treated with ethylene for 9 days had mesocarp watersoaking, epidermal sloughing, and lower hue (118°, control 124°), endocarp pH (4.4, control 5.4), and whole fruit firmness (23 N, control 46 N). Mature-stage fruit behaved similarly to Immature-stage fruit, but lacked mesocarp watersoaking. In contrast, after 9 days of ethylene exposure, the Breaker- and Yellow-stage fruit exhibited no watersoaking, accumulated beta-carotene in peel tissue (13.6 μg·g-1 F.W, control 0.35 μg·g-1 F.W.) and had a “melon”-like aroma. Ethylene exposure for all maturities increased respiration rate and decay incidence compared to air-treated fruit. Ethylene evolution was only detectable in fruit with visible decay. Decay incidence in response to ethylene treatment was inversely proportional to maturity at harvest. Watersoaking, exhibited exclusively in Immature fruit, spread inward from the epidermis starting after about 6 days of ethylene treatment. Cells in watersoaked tissue stained negatively for viability with fluorescein diacetate and cells proximal to watersoaked cells stained weakly compared to air-treated controls. Current work is focused on identifying the mechanism of cell death.
In this study, ripening characteristics, including color change and softening, were determined for tomato (Lycopersicon esculentum `Florida 47') fruit at immature-green through light red stages of development and subsequently treated with 1 μL·L–1 1-methylcyclopropene (1-MCP). Special attention was directed at comparing the responses of immature and mature-green fruit. Surface color and whole fruit firmness were measured every other day. 1-MCP delayed or slowed color changes and softening in fruit of every maturity class, with differences between control and treated fruit evident immediately following 1-MCP application for 24 h at 20 °C. Fruit treated with 1-MCP at early maturity stages (immature-green, mature-green, and breaker) exhibited an extended delay in external red pigment accumulation compared with control fruit. Fruit of all maturity classes developed acceptable final hue values (hue angle ≤55°), and the time required to reach these values declined with advancing fruit maturity. Immature-green fruit treated with 1-MCP did not attain an acceptable degree of softening during the specified storage periods examined before deteriorating due to shriveling and pathogen proliferation. 1-MCP-treated mature-green and breaker stage fruit did recover to acceptable firmness (5–10 N) and hue values but exhibited a severely reduced storage life thereafter compared with untreated fruit of equal maturity. Fruit at turning and more advanced stages exhibited reduced rates of softening and color development when treated with 1-MCP, yet they attained firmness and color values within the range of acceptability for commercial use. Fruit treated with 1-MCP at pink and light-red stages of ripening developed normal external color and exhibited significantly extended postharvest life due largely to a significant retention in firmness when compared to control fruit. Based on the studies described for `Florida 47' tomato fruit, 1-MCP would appear to be of little benefit and possibly detrimental if applied to early maturity fruit, most notably greens and breakers, due to irreversible limitations in the capacity of these fruit to soften to acceptable values. In sharp contrast, more advanced stage fruit, particularly pink and light red, responded to 1-MCP with significantly extended shelf-life due to retention of firmness.
Nonclimacteric commodities produce low levels of ethylene yet remain quite sensitive to the growth regulator. 1-Methylcyclopropene (1-MCP; SmartFresh Quality System), an inhibitor of ethylene action, allows analysis of the effects of endogenous ethylene on the senescence of nonclimacteric commodities during storage. Two commercial cultivars (Thoroughbred and Carlo) of fresh green beans (Phaseolus vulgaris L.) were treated with 0.5 μL·L−1 1-MCP followed by storage at 7 °C. 1-MCP was effective in delaying color change, brown spot incidence, and watersoaking in both cultivars. 1-MCP was effective at delaying yellowing as indicated by a decline in surface hue and chroma; however, lightness was not significantly different between control and 1-MCP-treated beans. Respiration in both cultivars was suppressed, but ethylene production was stimulated late during storage in response to 1-MCP. The appearance of brown spot, a surface disorder possibly reflecting low-temperature injury, was delayed by ≈5 days, and the progression of the disorder was reduced in 1-MCP-treated beans. The incidence of watersoaking in ‘Carlo’ was reduced by 50% in 1-MCP-treated compared with control beans. 1-MCP alleviated symptoms of senescence and chill injury of green beans during long-term storage, implicating a role for endogenous ethylene in the senescence of nonclimacteric commodities after harvest.