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Differential Response to Ethylene in Respiration and Ripening of Immature ‘Anjou’ Pears1


Treatment with 500 ppm ethylene for 24 hr or with 4000 ppm Ethrel (2-chloro-ethanephosphonic acid) dip for 30 sec resulted in ‘Anjou’ pears attaining full ripeness without a concomitant change in respiratory activity. A decrease in flesh firmness and increases in protein nitrogen and soluble pectin occurred, even though the fruit remained in the preclimacteric condition. This was shown by a positive response in rate of respiration to ethylene at the fully ripe stage. Continuous, 48- and 24-hr treatments resulted in comparable rates of ripening. However, while the continuous and 48-hr treatments induced the climacteric rise in respiration, the 24-hr exposure failed to do so. The effect of ethylene on respiration is independent from its effect on the initiation of ripening; a respiratory response probably requires a higher concentration or longer exposure to ethylene than does a ripening response.