Mechanism of action of endogenous plant growth substances in fruit set and early fruit development of kiwifruit

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Changes in the levels of endogenous plant growth substances in the pollinated and non-pollinated fruit and the parthenocarpic fruit induced by 5 ppm CPPU between the blooming and the early fruit growth stage, and effects of exogenous plant growth substances on induction of parthenocarpic fruit set and growth in 'Hayward' were investigated. In the pollinated fruit, the level of Z-like activity was at its peak 5 days after anthesis (DAA) and 20 DAA and GAs-like activities were at its peak 5 DAA. The level of ZR like activity was highest at anthesis and IAA-like substance was higher between 5 DAA and 9 DAA than another periods. In the parthenocarpic fruit, changes in their levels were similar to in the pollinated fruit When the treatment of Z, ZR and GA_3 (1000 ppm) were applied repeatedly just before anthesis (JBA) and 1 week after anthesis (WAA), parthenocarpy was induced. But fruit set percentages of the parthenocarpic fruits were lower and those fruit growth was remarkably inferior to … More the pollinated fruit. The treatment of 0.1 ppm CPPU and NAA (50 ppm) did not induced parthenocarpy. When the treatment of GA_3+NAA applied repeatedly JBA and 1 WAA, and GA_3 or NAA were applied JBA as first treatment and 0.1 ppm CPPU were applied 1 WAA as second treatment, parthenocarpy was induced. And those parthenocarpic fruit set and growth was superior to GA_3-induced one. When the treatment of GA_4 (1000 ppm) +4-CPA (50 ppm), GA_7(1000 ppm)+4-CPA, GA_4, GA_7, GA_7+-Z+4-CPA, Z+4-CPA and GA_4+GA_7+-Z+4-CPA were applied once JBA, parthenocarpy was induced. Treatments combined with 4-CPA promoted fruit growth and treatments combined with Z suppressed fruit growth Fruit growth of parthenocarpic fruit induced by GA_4+GA_7+Z+4-CPA was inferior to that induced by GA_7+Z+4-CPA. These results suggested that the high levels of GAs-or cytokinins-like activity, and GM-and IAA-like activity correlated strongly with fruit set of kiwifruit. On the other hand, the high levels of GAs-, cytokinins-and IAA-like activity correlated with early fruit development. Less