Inhibitory Factors That Affect the Ripening of Pear Fruit on the Tree

Pear (Pyrus communis L.) fruit are not usually allowed to ripen on the tree. Indeed, they are harvested at the mature green stage and ripened off the tree. In this study, we examined inhibitory factors that affect the ripening of pear fruit on the tree. The relationship between ethylene and fruit abscission was investigated in 'Bartlett' pears. Fruit at the mature green stage produced little ethylene, but most fruit rapidly produced ethylene 2-3 days before dropping. Fruit drop was stimulated by ethylene treatment of fruit on the tree, but was delayed by treatment with 1-methylcyclopropene. We also investigated how fruit ripening on the tree was affected by a continuous supply of assimilates to the fruit via phloem transport. To suppress phloem transport, a girdling treatment was applied to the branch above the abscission zone. Fruit ripening on the tree was promoted by this girdling treatment, but the fruit dropped before softening to an edible firmness. 1-Naphthaleneacetic acid (NAA) was highly effective in suppressing fruit drop. NAA treatment alone did not induce full ripening on the tree, but fruit did ripen on the tree when the NAA and girdling treatments were combined. Two factors may explain why pear fruit do not fully ripen on the tree: the production of ethylene by the fruit during ripening on the tree does not occur until after the optimal harvest time and the continuous supply of assimilates to the fruit via phloem transport may delay ripening.