Effect of plant regulators on set and berry development in certain seedless and seeded varieties of Vitis vinifera L.

Flowering clusters on ungirdled, nondefoliated shoots of 'Black Corinth', and girdled shoots defoliated to 1 /ia leaf, were dipped in 4-CPA at 15 ppm, or GA3 at 5 or 15 ppm. In nondefoliated shoots the set was decreased about 13 °/o at 15 ppm, but there were no significant differences among the other treatments. All treatments produced heavier rachises, berries, and clusters than the ungirdled, untreated controls. In defoliated shoots the set was decreased approximately 85 °/o by GA3 at 15 ppm. 4-CPA significantly increased set, but a mixture of GA3 and 4-CPA did not alter set.Similar experiments were carried on with the seeded varieties 'Pinot Chardonnay', 'Muscat of Alexandria', and 'Grenache'. Clusters on ungirdled nondefoliated shoots were dipped in GA3, 4-CPA, or a mixture of the two compounds. Like treatments were made on other clusters on shoots defoliated to 1/4 leaf. There was a varietal difference in response among the seeded varieties. The compounds injured the Muscat and reduced the set and berry size.All treatments increased the set of seedless berries on nondefoliated shoots of 'Pinot'. In both 'Chardonnay' and 'Grenache' there was a shift from seeded to seedless berries. Application of 4-CPA resulted in a significantly greater set in total number of berries on defoliated shoots of 'Chardonnay' and 'Muscat'.All solutions containing GA3 increased siz'e of seedless berries on nondefoliated shoots of 'Pinot'. GA3 applied at shatter stage increased size of seedless 'Muscat' berries. With one exception, there was no increase in size of one-, two-, or three-seeded berries.Percentage set was significantly increased in defoliated shoots of 'Muscat' by 4-CPA, and in 'Pinot' by 4-CPA or a mixture of 4-CPA and GA3.A kinin, benzyladenine, failed to increase set or berry size, but intensified the development of a purple anthocyanin pigment in 'Muscat'.The possible importance of the ratio of a leaf-produced set factor to gibberellin in berry set in 'Black Corinth' is discussed