Effects of three plant growth regulators on kiwifruit development

The effects of cytokinin, auxin and gibberellins on kiwifruit development, alone and in combination, have been studied in a commercial kiwifruit orchard. Several parameters such as fruit weight were measured. The combination of three growth regulators (2,4-D, CPPU and GA(3)) applied 43 days after full bloom (at 25, 50 and 10 mg/kg, respectively) increased the yield expressed as fresh weight. Fruit size also increased but fruit shape did not change. Application of 2,4-D alone was the most effective treatment in increasing fruit size, weight and production, while application of CPPU alone produced smaller increases. Fruit treated with GA3 alone did not differ from controls. When growth regulators were applied together, combining two or all three, there was a positive synergistic effect which increased fruit size. All combinations increased kiwifruit growth in all cases shifting it towards larger commercial standard weights. In addition, fruit diameters and length were analyzed to obtain growth kinetic curves. Our fresh weight data fitted a monomolecular kinetic curve for all combinations, except when all three plant regulators were combined together, in which case values fitted to a linear model, while all the dry weight kinetic curves fitted a linear model.