Influence of Gibberellic Acid on Setting and Development of Fruits in Tomato.

Considering the total number of investigations concerned with gibberellic acid those dealing with fruits are relatively few (1-13). Gibberellic acid (GA) is capable of inducing parthenocarpy (1, 3, 5, 6, 7, 13), but whether or not fruit setting is increased at the same time is not known (4,6, 12). Several investigators found no increase in fruit size with GA treatment (4, 6, 10), but investigators did find considerable increase in the size of the grape berry (8, 9, 10, 11). There is thus room for more work with GA on fruiting. In 1957 the writer set up three experiments for studying the effect of GA on setting and development of fruit in Lycopersicum esculentum Mill. var. John Baer. Early in February an experiment with 2 foot John Baer tomato plants in 6 inch pots was set up in the greenhouse. The purpose was to make a comparative study of indoleacetic acid, 2, 3, 6-trichlorobenzoic acid and gibberellic acid on induction of parthenocarpic fruits. These growth regulators were incorporated in lanolin pastes both alone and in combinations with GA in the following concentrations: 1.0 and 0.5% IAA; 0.1% 2,3,6-TCBA; 1.0 and 0.5% GA; 0.5 % IAA + 0.5 % GA, and 0.1% 2,3,6TCBA + 0.25 % GA. These pastes were applied to the cut surface of the pistil of emasculated flower buds, ready to open. Only the first two buds in each cluster were used; the others were removed. Seventy-four mature fruits were harvested. Of these, 16 produced by pollination were seeded; all others were seedless. The seedless fruits produced by applying growth regulators were a little smaller than the seeded ones. The GA treatment alone induced parthenocarpy: adding growth regulators to the GA did not alter the percent setting or the size of the fruits. This is different from the report of Luckwill (3), in which he states that there was a synergistic effect when the growth regulators were added to GA. In late April a second experiment was started (also in the greenhouse), with 36 plants approximately 30 inches tall. In this experiment there was