Effect of Elevated Temperature on Ripening of ‘Bartlett’ Pear, Pyrus communis L.1

At any stage of the ripeness of ‘Bartlett’ pear fruits, subsequent ripening was inhibited if the fruits were warmed to 40°C. Both production of, and sensitivity to, ethylene (C 2 H 4 ) were almost totally suppressed. Even at 30°C, C 2 H 4 production was greatly reduced in both early- and late-season fruit. Unless treated with C 2 H 4 , early-season fruit failed to ripen at 30°C although late-season fruit ripened spontaneously, presumably because of high internal concentrations of the gas. In both cases ripening was characterized by a watery breakdown of the floral end of the fruit. At 40° and 50°C, respiratory rates declined progressively unless the fruits were treated with C 2 H 4 , whereupon a stimulation occurred although ripening was unaffected. Gas exchange was not limiting at temperatures as high as 50°C, even when the ends of the fruits were sealed with paraffin wax. Maximum modification of the internal atmosphere of any individual fruit resulted in 15.7% O 2 and 7.2% CO 2 . Ripening of fruits held at 20°C in that atmosphere was delayed about 3 days, presumably via mild competitive CO 2 inhibition of C 2 H 4 action. We conclude that failure of ‘Bartlett’ pears to ripen at 40°C results from lack of C 2 H 4 production and loss of sensitivity to the gas. The mechanisms are unknown.