The action of gibberellins on the fruiting of grapes

1. Inquiries were undertaken to make clear the action of gibberellins (GB crystals for testing were kindly provided by the Japan Gibberellin Association) upon the fruiting of grapes, such as "Delaware" and "Campbell-Early" varieties, during past 8 years from 1958 through 1965. Treatments with gibberellin (100 ppm GB solution added with 100 Airrol-op as wetter) were carried out on the very young clusters through twice dipping at the date of 15 days before and of 10 days after the full-bloom, respectively. The present paper concerns with the responses of grapes to GB for the enlargement of flower-clusters and berries, frequency of berry set, formation of seedless berries, hastening of maturity, and for the abortion of pollen-grains and of ovules. Histological observations were also made throughout growing processes in those artificially induced seedless berries. 2. When the flower-clusters were dipped in GB solution 15 days before the date of full-bloom, the flowering has been remarkably hastened, i.e., 3 or 4 days earlier than that of non-dipped ones. When GB applied to the young clusters of "Delaware" before the full-bloom, the treated fruitclusters attained at the time of harvest to the significantly longer size as compared with controls. In "Campbell-Early", however, anomalous responses, such as thickening, hardening, crooking and twisting of cluster-peduncles have resulted with different degrees by such pre-bloom GB treatment. 3. When flower-clusters of "Delaware" were dipped in GB solution at the most suitable time, which came twice at 15 days before and as well as 10 days after the date of full-bloom, seedless berries were formed in the treated clusters with more than 95% frequency, and the fruits thus obtained were superior in quality and well marketable as the new seedless grapes. On the other hand "Campbell early", which was also treated with GB at the most proper time, could induce seedlessness with less than 50% of berries per cluster, at the maximum, not attaining the level of commercial usage as in "Delaware". 4. Only one GB treatment at the proper time of after the full-bloom could cause usually more or less striking enlargement of berries. But the additional one or three GB treatments after the fullbloom, however, could not increase any more the extent of enlargement beyond that of single GB application. Experiments with "Campbell-Early" could raise nearly the same result as that with "Delaware". Sizes of seedless berries in both the varieties, however, did not attain those of normal seeded berries set on the untreated clusters. 5. In "Delaware", both the seeded and seeldess berries of the clusters treated properly with GB were no less promoted in their colouring towards maturity, and the seedless young berries on the treated cluster indicated that their Brix was increased but their acidity was decreased in turn. Towards ripening the juice of seedless berries became to show higher Brix, and rather high acid content in contrast to advanced colouring of their skins. Result of experiments carried out during 7 years showed clearly that the harvesting date of seedless grapes could be hastened definitely for the period of from 12 to 20 days as compared with that of untreated grapes. The "Campbell-Early" could reveal quite similar results as those of "Delaware". 6. According to the results obtained during 4 years by the experiment of "Delaware", the number of seedless berries per cluster induced by GB application increased significantly as compared with that of seeded berries on an untreated cluster. "Campbell-Early" clusters dipped in GB before the time of full-bloom produced usually a number of small shot-berries, mixed with normal berries, and much more frequent occurrence of shot-berries has resulted from the twice applications of GB. But "Delaware" clusters treated with GB did not respond at all to the stimulus of GB for the formation of shot-berries even under the twice or still more applications. 7. The pollen-grains collected from the GB treated flowers did not show any morphological differences from those of controls, but their germinating power was more or less weaker than the controls under the artificial tests. In order to determine the reproductive power of those pollengrains, untreated and emasculated flowers were artificially pollinated with the pollen-grains obtained from the treated flowers. Consequently, the percentage occurrence of normal seeded berries was remarkably lower than in the berries from pollinated flowers. From such results, the pollen-grains formed in the GB treated flowers showed clearly a certain weakness in their fertilizing power. 8. When emasculated flowers of GB treated clusters were pollinated with the normal pollengrains collected from untreated intact flowers, the rate of occurrence of normal seeded berries per cluster attained to less than 5%, showing quite similar state realized under open-pollination of those treated flowers. It becomes evident that the ovu ...