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Jennifer R. DeEll, H.P. Vasantha Rupasinghe, and Dennis P. Murr

`Cortland' is an apple cultivar with inherent poor storeability because of excessive vulnerability to the development of superficial scald in long-term storage. The objectives of this investigation were to evaluate the potential of the potent ethylene action inhibitor 1-methylcyclopropene (1-MCP; EthylBloc®) to counteract this constraint and to develop some basic procedures for its exposure. Eight hours after harvest, fruit were exposed to 1.0 mL·L–1 1-MCP for 0, 3, 6, 9, 12, 16, 24, or 48 h at 3, 13, or 23 °C. Following exposure, fruit were placed at 0 to 1 °C in air for 120 days, after which time they were removed to 20 °C and held 7 days for post-storage assessment of ripening and to allow development of physiological disorders. In general, and within our experimental limits, the higher the temperature of 1-MCP exposure the shorter the required exposure time to obtain similar effects. The desired effectiveness of 1-MCP could be achieved by exposing fruit for at least 3 h at 23 °C, for 6 h at 13 °C, or for 9 h at 3 °C. 1-MCP-treated apples were consistently 2 kg firmer than untreated apples. Scald incidence in untreated fruit after 120 days at 0 to 1 °C and 7 days at 20 °C was 100%, whereas 1-MCP reduced scald by 95% in treatments of long enough duration at any particular temperature.

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Jiwon Jeong, Jeffrey K. Brecht, Donald J. Huber, and Steven A. Sargent

A study was conducted to determine the effect of 1-methylcyclopropene (1-MCP) on textural changes in fresh-cut tomato (Lycopersicon esculentum, Mill.) slices during storage at 5 °C. The relationship between fruit developmental stage and tissue watersoaking development was also determined. Fresh-cut tomato slices prepared from light-red fruit that had been exposed to 1-MCP (1 μL·L-1 for 24 h at 5 °C) retained significantly higher pericarp firmness during storage at 5 °C for 10 d than slices from nontreated fruit or slices stored at 10 or 15 °C and they also had a significantly higher ethylene production maximum. 1-MCP (1 or 10 μL·L-1 for 24 h at 5 °C) had no affect on the firmness of fresh-cut, red tomato slices at 5 °C or on slices prepared from 5 °C-stored, intact red tomatoes. Nor did 1-MCP treatment have a significant effect on electrolyte leakage of tomato slices or intact fruit stored at 5 °C. Slices from fruit of the same developmental stage but with higher initial firmness values had less watersoaking development and responded better to 1-MCP treatment during 8 d storage at 5 °C. 1-MCP (1 μL·L-1) was more effective in reducing watersoaking in light red stage tomato slices when applied at 5 °C for 24 h compared with 1-MCP applied at 10 or 15 °C. Watersoaking development was also more rapid in fresh-cut tomato slices as initial fruit ripeness advanced from breaker to red stage. Our results suggest that watersoaking development in fresh-cut tomato slices is an ethylene-mediated symptom of senescence and not a symptom of chilling injury as had previously been proposed.

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Michelle L. Jones, Eun-Sun Kim, and Steven E. Newman

Geraniums are sensitive to ethylene during shipping and respond by abscising their petals. Treatment of stock plants with ethylene (ethephon) in order to increase cutting yield resulted in earlier flowering in Pelargonium × hortorum `Kim' and `Veronica', but did not result in increased susceptibility to petal abscission following exposure to 1.0 μL·L-1 ethylene. Treatment of `Kim', `Veronica', `Fox', and `Cotton Candy' with 1.0 μL·L-1 ethylene resulted in increased petal abscission within one hour, with `Fox' being the most sensitive and `Kim' the least. Pretreatment of florets with 1-MCP for 3, 6, 12, or 24 hours at concentrations of 0.1 or 1.0 μL·L-1 decreased petal abscission in all cultivars following exposure to 1.0 μL·L-1 ethylene. Treatment with 0.1 μL·L-1 1-MCP for 1 hour reduced petal abscission rates in ethylene treated florets to that of non-ethylene treated controls in all cultivars except Fox. `Fox' florets, which are more sensitive to ethylene, required 12 to 24 hours of exposure to 1-MCP to reduce petal abscission rates to that of control flowers. Pretreatment of geranium plants with 1-MCP can be used to reduce petal shattering during shipping. Chemical names used: 2-chloroethanephosphonic acid (ethephon); 1-methylcyclopropene (1-MCP).

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Dan D. MacLean, Dennis P. Murr, Jennifer R. DeEll, and Eugene Kupferman

The ethylene antagonist 1-methylcyclopropene (1-MCP) was investigated for its potential impact on the transcription of key flavonoid biosynthetic (PAL and CHS) and ethylene perception (ERS1) genes during the postharvest storage of pear (Pyrus × communis L.). Optimally harvested red and green `d'Anjou' fruit were treated with 1 μL·L-1 1-MCP for 24 h at 0 °C to 1 °C, and subsequently placed in cold storage (0–1 °C, 90–95% RH). Fruit were removed every 21 days for 126 days, and evaluated for firmness, TSS, and ethylene and volatile production for up to 10 days (≈21 °C). Tissue samples were collected for Northern blot analysis and determination of flavonoid and chlorogenic acid content. PAL content increased during the 1-week simulated marketing period irrespective of storage duration, which coincided with an increase in respiration and ethylene content. Although it was still detectable, total PAL content was dramatically reduced by the 1-MCP treatment. CHS was abundant immediately after harvest and after removal from storage, but declined rapidly thereafter, and was not detectable after 1 week at room temperature. The 1-MCP treatment further exacerbated this decreasing trend in CHS content. ERS1 content appears to be stable throughout storage and the simulated marketing period, with levels lower in 1-MCP-treated fruit. These results suggest that 1-MCP significantly inhibits the transcription of key flavonoid and ethylene regulatory enzymes, possibly compromising the nutraceutical content of pear fruit. The increase in PAL with the concomitant decrease of CHS after removal from storage suggests a diversion of carbon from flavonoid compounds into simple phenols, such as chlorogenic acid.

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R. St.Hill and D.P. Murr

Recent advances in technology have made the snapdragon, Antirrhinum majus L., a promising florist crop in North America and potentially on the Ontario market. CO2 is a known inhibitor of ethylene action, but its effects tend to be difficult to interpret based on the variable responses of plants to this gas. Recently, a gaseous ethylene analog has been shown to inhibit certain ethylene responses of cut flowers, such as wilting in carnations and flower abscission of cut phlox. This cyclic olefin, 1-methylcyclopropene (1-MCP), is thought to bind irreversibly to the ethylene receptor sites, thereby preventing or delaying ethylene responses. In the experiments undertaken, the potential of CO2 and 1-MCP were investigated for their ability to enhance vase life and to reduce shattering and wilting of snapdragons. Flowers were sealed in ≈0.2-m3 chambers encased in 6-mil polyethylene and exposed to elevated CO2 (5% or 10%) or 1-MCP (20-200 nL/L) for 6 to 24 h at 20 °C. The flowers were then exposed to continuous ethylene of 0-20 μL/L. Following exposure to 5 or 20 μL/L ethylene, 1-MCP reduced shattering ≈2- to 3-fold compared to CO2 treatment. 1-MCP did not prevent the wilting response but delayed it by ≈2 days. CO2-treated flowers exhibited a more rapid decline in net percent open florets from days 3 to 5 post-treatment. Despite the ability of 1-MCP to reduce shattering, in the absence of exposure to continuous ethylene, it has limited effectiveness on wilting compared to CO2.

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H.P. Vasantha Rupasinghe, Dennis P. Murr, Jennifer R. DeEll, and Murray D. Porteous

Flesh softening is a major quality parameter that can limit long-term storage of apple cultivars. This study investigated the combined effects of preharvest AVG (Retain™) application, 1-methylcyclopropene (1-MCP; EthylBloc™) exposure at harvest, and commercial controlled atmosphere (CA) storage (2.0% O2 + 2.5% CO2) on flesh softening of `Empire' apple. Treatments were assigned in a split-split-plot experimental design; AVG and no AVG application as the main-plot, CA and air storage as the sub-plots, and 0, 0.1 0.5, 1.0 mL·L–1 1-MCP as the sub-sub-plots. Apples were removed from storage at 70 and 140 days after harvest and kept up to an additional 2 weeks at 20 °C for post-storage assessment of ripening. Preharvest AVG application of `Empire' fruit delayed maturation slightly as determined by starch index at harvest, but did not affect fruit size at harvest nor flesh softening in storage. All levels of 1-MCP were equally effective in controlling fruit softening both in air and CA, as 1-MCP-treated fruit were ≈2.5 kg firmer than untreated fruit. This firmness advantage was still evident even after 2 weeks at 20 °C, with CA-stored fruit holding their firmness the best. When all three technologies were combined, treated fruit were overall 156% firmer than control fruit (no AVG, no 1-MCP, air-stored). As well, ethylene production and emanation of aroma volatiles were reduced significantly in these fruit. Therefore, the synergism of AVG, 1-MCP and long-term CA storage could potentially hold flesh firmness and other ripening parameters of apples to values near those found at harvest.

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Lin Shen* and Jiping Sheng

Chinese Winter Jujube (Zizyphus jujuba Mill.) is a kind of new fresh consumed jujube fruit with high quality originated in China, but its postharvest shelf-life is short at room temperature (often 7 days). A study was conducted to determine the effect on 1-methylcyclopropene (1-MCP) on changes in ethylene production, respiration rate, firmness, electrolyte leakage and vitamin C. Chinese Winter Jujube fruits harvested at half-red stage, were randomized into rigid, vented containers (0.5 m3; n = 5), treated with 1 μL·L-1 for 12h at room temperature (20 ± 2 °C), then stored at 20 °C. Fruits treated with 1-MCP had significant lower ethylene production, it showed 21% lower (0.128 μL·kg-1 per hour) at 8th day. Respiration rate had no significant difference between treated and control during the 12d storage. Firmness of treated fruits was from 15.4% to 26.3% higher than that of control, while the electrolyte leakage was from 12.2% to 27.4% lower than that of control. The content of vitamin C by 1-MCP treatment was 11.2% higher than control at the last day of storage (368 mg/100 g). The results indicated that 1-MCP had positive results on maintaining postharvest shelf-life of half-red stage of Chinese Winter Jujube fruit.

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John M. DeLong, Robert K. Prange, Conny Bishop, Peter A. Harrison, and Daniel A.J. Ryan

To determine if postharvest treatments of 1-methylcyclopropene (1-MCP) retard the senescence of highbush blueberries (Vaccinium corymbosum L.) removed from storage, `Burlington' (early) and `Coville' (late) fruit were harvested from four experimental sites and treated for 24 hours at 20 °C with 0 (control), 25 (low), 100 (medium), or 400 (high) nL·L-1 of 1-MCP. All fruit were then stored in a controlled atmosphere of 10-15 kPa O2 and 10 kPa CO2 at -1 to 1 °C for 4, 8, and 12 weeks, followed by a 20 °C shelf-life of up to 20 days. During the shelf-life period immediately after harvest and those following each storage removal, percent marketable fruit (PMF) were calculated daily as: [fruit in good condition]/[total berry number] × 100. Changes in PMF were not affected by 1-MCP treatment; hence, we conclude that 1-MCP at rates up to 400 nL·L-1 does not alter the shelf-life quality of the highbush blueberry cultivars tested.

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R.E. Moran

The objective was to test the efficacy of 1-MCP when applied at 1, 4, 7, or 10 days after harvest. At harvest, internal ethylene (IEC) was undetectable in most fruit. There was a large increase in concentration at 7 days after harvest and an additional increased at 10 days in `McIntosh'. In Cortland, IEC was very low or undetectable until 10 days after harvest. After 4 months in CA storage, firmness of untreated `McIntosh' fell below 53 N. 1-MCP applied 1 day after harvest maintained firmness more than later applications. Application at 4–10 days was also effective with little difference between the three dates. 1-MCP was most effective on `Cortland' when applied 1–7 days after harvest. At 10 days, there was a loss of efficacy in maintaining firmness. Similar results occurred after 7 months of CA storage. Superficial scald of `McIntosh' was very mild with <1% of the fruit being affected after 220 days storage and 7 days at 20 °C. Untreated `Cortland' fruit had the greatest incidence of scald with most of the fruit being affected by 200 days. 1-MCP was not effective in preventing scald in `Cortland'.

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Susan S.C. Liou and William B. Miller

During transportation and storage of Dutch tulip bulbs, potential ethylene exposure could lead to flowering abnormalities, including accelerated flowering, shortened plant heights, and in the most extreme case, flower abortion. Sources of ethylene include Fusarium-infected bulbs, deteriorating tissues, and combustion engines. Treatment with 1-MCP (1-methylcyclopropene) may prevent ethylene action as 1-MCP occupies ethylene specific receptors on target tissue. Two aspects of this problem were quantified using four tulip cultivars: duration of ethylene exposure necessary to induce damage as well as the effective period of protection by 1-MCP against ethylene. Flower abortion appeared in susceptible cultivars after ≥9 days of ethylene exposure (10 ppm) and was only found in mature bulbs (late November). The effective protection period of 1-MCP against ethylene (2-week exposure of 10 ppm) was determined, using flowering percentages, to be as long as 4–7 days in young bulbs and 28 days for older bulbs. Effects of ethylene on other flower attributes and implications of these findings in industry practices will be discussed.