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