Morphological studies of gibberellin-induced parthenocarpic and asymmetric growth in apple and Japanese pear fruits

Abstract

1. Morphological differences between seeded and parthenocarpic fruits induced by GA₄ and GA₇ were documented in Wealthy apple and Japanese pear cv. Shinseiki fruits. GA-induced parthenocarpic fruits were characterized by a larger polar diameter and an equal or smaller transverse diameter than seeded fruits. Cortex thickness of seeded fruits was greater in the basal than median or apical region; whereas, in parthenocarpic fruits cortical thickness was greater in the apical than median or basal areas. The thicker cortex in the basal region of seeded fruit was related to cell number. The apical region of parthenocarpic apples contained a greater number and larger cells and in Japanese pears larger cells than in the basal or median sections. Cell division in the cortex of seeded and parthenocarpic apples ceased 3 to 4 weeks and in Japanese pear 4 to 5 weeks after bloom.
2. Asymmetric fruit growth was induced in seeded and parthenocarpic apple and Japanese pear fruits following a localized application of GA to one side of the fruit 2 weeks after bloom. Both cell number and size increased in the treated side as compared to the non-treated side in both apple and Japanese pear. Greater response was observed in parthenocarpic than seeded fruit. In Japanese pear there was a striking increase in cortex thickness (cells size and number) of the treated side compared to nontreated side even when treated with GA₇ 4, 6 and 8 weeks after bloom. GA₃ failed to induce asymmetric fruit growth in Japanese pear regardless of time of application.