Exogenous ethylene accelerates ripening responses in Bartlett pears regardless of maturity or growing region

Mature-green 'Bartlett' pears (Pyrus communis L.) were harvested weekly during the commercial harvest period to explore the influence of three climatically diverse growing locations and of harvest maturity on the requirement for C2H4 treatment at harvest to achieve uniform ripening and good eating quality. Pears were treated with ethylene (air + 10 Pa C2H4) or air (untreated) at 20°C for 24 h to determine their responsiveness to C2H4, including the effect on 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACC-S) and ACC oxidase (ACC-O) activity during subsequent ripening at 20°C. Exposing freshly harvested and non-chilled 'Bartlett' pears to 24 h exogenous C2H4 treatment concurrently stimulated the activity of ACCS and ACC-O, and resulted in higher C2H4 production, which advanced the rate of ripening and reduced the firmness variability regardless of maturity, growing region or season. Differences in the rate of softening between ethylene-treated and untreated pears were greatest for fruit from earlier harvest dates. The ripening capacity of 'Bartlett' pears developed as the fruit matured on the tree, resulting in higher ACC-S activity, ACC-O activity and C2H4 production, but the ripening capacity was not fully induced unless the fruit were cold stored or treated with exogenous C2H4. Ethylene production was higher in fruit from growing locations that experience cooler preharvest temperatures and fruit from later harvests within each location. Pears harvested from warmer growing regions as well as early harvests from later growing locations which experience cooler preharvest night temperatures can benefit from treatment with C2H4 after harvest to promote uniform ripening.We gratefully acknowledge the invaluable help and advice of Murray Clayton on statistical analysis. We thank David Bouck, George Sakaldasis and Michelle Lauer for their excellent technical assistance. We also thank Doug Hemly of Greene and Hemly, Inc., David Elliot of David J. Elliot & Sons, Tom Thomas of Alex R. Thomas & Co., and Don Eutiner for their cooperation and donation of fruit used in this study. Research was supported in part by the California Pear Advisory Board

Temperature and exposure time during ethylene conditioning affect ripening of Bartlett pears

PubMedID: 10691611Freshly harvested early- and mid-season Bartlett pears (Pyrus communis) were treated with ethylene (air plus 10 Pa C2H4) or air at 5, 10, and 20 °C for 24 and 48 h (experiment 1) and at 5 and 10 °C for 48, 72, and 96 h and at 20 °C for 24 h (experiment 2). Following C2H4 or air treatment at different temperatures and durations, pears were transferred to 20 °C in air for ripening. Bartlett pears were evaluated for firmness, color, respiration, C2H4 production, and activities of 1-aminocyclopropane-1-carboxylic acid synthase (ACC-S) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO). Ethylene action was temperature dependent. The duration of C2H4 conditioning needed to fully induce ripening was longer at lower temperatures: 72 h at 5 °C, 48 h at 10 °C, and 24 h at 20 °C. Cold storage in air for as little as 3-4 days at 5 or 10 °C appeared to hasten subsequent ripening, but to a lesser extent than pears kept for 2 weeks at - 1 °C in air. Despite a significant increase in ACC-S activity in pears treated with C2H4 at 5 °C, there was not a simultaneous increase in ACC-O activity, resulting in low C2H4 production that was insufficient to generate the threshold endogenous levels of C2H4 required for ripening. Contrary to previous findings with pears, these data indicate that ACC-O could be a rate- limiting step in C2H4 biosynthesis

Cold storage duration influences ethylene biosynthesis and ripening of 'Bartlett' pears

Ripening behavior of 'Bartlett' pears (Pyrus communis L.), with or without ethylene (C2H4) treatment, was assessed at harvest, and after 2, 4, 6 and 12 weeks of cold storage at -1 °C. Fruit exhibited increasing rates of C2H4 production and consequently faster ripening rates with increased length of cold storage. Ripening characteristics were influenced by storage duration, but to different degrees. The data indicate that the threshold C2H4 concentration for softening may be lower than that for color change from green to yellow. Ethylene treatment for 24 h at harvest resulted in a rate of ripening equivalent to that following cold storage for 2 to 4 weeks, depending on the orchard location. Storage for 12 weeks significantly increased C2H4 production upon transfer to ambient temperature, indicating that fruit were reaching the end of their storage life. 'Bartlett' pears may ripen to a firmness of 14 N (ready to eat) at 20 °C within 2.5 to 7 days depending upon the duration of prior cold storage

Sensory quality of 'bing' sweet cherries following preharvest treatment with hydrogen cyanamide, calcium ammonium nitrate, or gibberellic acid

'Bing' sweet cherry (Prunus avium L.) trees were treated with hydrogen cyanamide (CH2N2) or calcium ammonium nitrate (CaNH 4NO3) during dormancy, or gibberellic acid (GA 3) 26 days before harvest during three consecutive years. Fruit were evaluated at harvest for sensory taste quality using twenty trained panelists sampling for firmness, sweetness, tartness, and cherry flavor. Nondestructive instrumental firmness preceded destructive sensory firmness on the same untreated and GA3-treated cherries in one year when used as a supplementary evaluation. Sensory firmness was consistently higher in GA 3 fruit and to a lesser extent in CH2N2 fruit than in CaNH4NO3 and untreated fruit. Instrumental firmness of GA3 fruit did not increase significantly compared with untreated fruit yet instrumental firmness of each treatment correlated relatively well with perceived sensory firmness. Sensory sweetness and cherry flavor scored very similarly, yet both attributes simultaneously varied between treatments across the years. Perceived sensory tartness of treated fruit was variable among years; yet, on average, was rated among treated and untreated fruit as similar. Under the assumption that elevated sensory firmness, sweetness, and cherry flavor intensity reflects improved sweet cherry quality, GA3 fruit were rated of higher quality than untreated fruit given their increased firmness and similar or occasionally elevated sweetness and cherry flavor intensity. CH2N2 fruit maintained quality similar to that of untreated fruit, despite often having marginally higher firmness, due to similar or reduced ratings for sweetness and cherry flavor intensity. Notwithstanding similar firmness between CaNH4NO 3 and untreated cherries, sensory quality of CaNH4NO 3-treated cherries was reduced due to their often-diminished levels of perceived sweetness and cherry flavor

Postharvest quality of 'Bing' cherries following preharvest treatment with hydrogen cyanamide, calcium ammonium nitrate, or gibberellic acid

During three consecutive years, 'Bing' sweet cherry (Prunus avium L.) trees were treated during dormancy with the dormancy-manipulating compounds, CH2N2 or CaNH4NO3, or were treated with the plant growth regulator GA3 at straw color development. Fruit of a range of maturities, based on skin color, were evaluated for quality following harvest and simulated transit and market storage conditions. At comparable maturities, CH2N2 and GA3 fruit were of similar firmness and were consistently firmer than CaNH4NO3-treated and untreated fruit across years, storage regimes, and maturities. CaNH4NO3 and untreated fruit were of similar firmness. CH2N2-treated cherries were larger than fruit of other treatments, but only marginally with respect to variation in fruit size between years. Contraction of fruit diameter occurred after 3 days storage, but ceased thereafter up to 11 days storage. Soluble solids and titratable acidity varied between years, storage regimes, and maturities. Strong interactions of treatment and year concealed possible treatment effects on these indices. GA3 fruit contained fewer surface pits in one year while CH2N2 fruit suffered less shrivel in another. The earlier harvest date for CH2N2 fruit often avoided higher field temperatures and the resulting promotion of postharvest shrivel. Pitting and shrivel were more prevalent in stored fruit. Brown stem discoloration developed in storage, occurring most frequently in mature fruit, although methyl bromide-fumigated fruit were particularly susceptible. This disorder was more common in GA3 fruit during years of high incidence. Chemical names used: gibberellic acid (GA3); calcium ammonium nitrate (CaNH4NO3); hydrogen cyanamide (CH2N2)

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