Effects of Gibberellic Acid
- Overcoming dormancy. Treatment with high concentrations of GA is effective in overcoming dormancy and causing rapid germination of seed. Concentrations of about 2 ppm can cause tubers to sprout earlier.
- Premature flowering. If a plant is sufficiently developed, premature flowering may be induced by direct application of GA to young plants. This action is not sustained and treatment may have to be repeated. Formation of male flowers is generally promoted by concentrations of 10 to 200 ppm., female flowers by concentrations of 200 to 300 ppm. Concentrations of more than 600 ppm markedly suppresses initiation of both male and female flowers.
- Increased fruit set. When there is difficulty with fruit set because of incomplete pollination, GA may be effectively used to increase fruit set. The resulting fruit maybe partially or entirely seedless. GA has increased the total yield in greenhouse tomato crops both as a result of increased fruit set and more rapid growth of the fruit.
- Hybridizing. Pollination within self-incompatible clones and between closely related species may some times be forced by the application of GA and cytokinin to the blooms at the time of hand pollination.
- Increased growth. GA applied near the terminal bud of trees may increase the rate of growth by stimulating more or less constant growth during the season. In a Department of Agriculture experiment, the GA was applied as a 1% paste in a band around the terminal bud of trees. Treatment was repeated three times during the summer. Walnut tee growth was 8.5 ft. for treated trees, 1.5 ft. for untreated trees.
- Frost protection. Spraying fruit trees at full-blossom or when the blossoms begin to wither can offset the detrimental effects of frost.
- Root formation. GA inhibits the formation of roots in cuttings.
Concentration-----parts/million GA-------mg Water ml (cup)------Purpose
50--------------------------125------------2400 (10 1/2)------------------------Early flowering
200------------------------125------------600 (2 1/2)----------------------------Early flowering
800------------------------125------------160 (2/3)-------------------------------Blossom set
2000-----------------------125------------60 (1/4)--------------------------------Seed germination
1% paste-----------------125------------5 ml (1 tsp.)--------------------------Growth promoter