Effects of Exogenous Growth Regulators on Fruit Development in Citrus unshiu

Abstract The effects of applied growth regulators on fruit development have been determined in the parthenocarpic Satsuma mandarin (Citrus unshiu Marc.). The application of either gibberellic acid or benzyladenine at flower opening, caused a transient increase in cell division in the ovary wall, but had no significant effect on final fruit size. Late fruit growth and final fruit size were increased by the application of the synthetic auxin 2,4,5-trichlorophenoxyacetic acid, which had a specific effect on the enlargement of the juice vesicles. The three growth regulators enhanced vascularization in the pedicel, but the growth effects observed were unrelated to their influence on the transport capacity of the phloem but caused by their direct effects on the fruit tissues. The sensitivity of the fruit tissues to the applied growth regulators changed markedly during early fruitlet development, and was characterized culturing the fruit tissues in vitro.