Husbandry and hormonal factors which influence inflorescence initiation in Vitis vinifera cv. Chardonnay

C-16, 17 dihydro GA₅, a novel growth retardant was applied to the first 10 developing axillary buds of actively-growing Vitis vinifera shoots to investigate the effect on spring shoot growth and inflorescence initiation the following season. Six treatments included 0.00µg, 0.33µg, 1.00µg, 3.33µg, 10.00µg and 33.33µg C- 16,17 dihydro GA₅ applied by microdrop directly onto the axillary bud of Mendoza Chardonnay. The following season shoot growth from the labelled buds was measured, as were inflorescence (bunch) number and fruit mass. The application of C-16, 17 dihydro GA₅ had no effect on shoot growth, bunch number or bunch mass the spring following application to developing axillary buds. Trials were undertaken to investigate the relationship between the developing leaf, and the initiating bud. Defoliation treatments were applied to the first 10 nodes on actively-growing shoots of Mendoza Chardonnay. Treatments included no, alternate and total defoliation. Defoliation consisted of removing the leaf subtending the developing bud by pinching the petiole at the leaf sinus (avoiding damage to the axillary bud). The following season shoot growth from the labelled buds was measured, as were inflorescence (bunch) number and fruit mass. Total defoliation reduced bud fertility and fruit mass the following season. The rate of spring shoot growth was increased with defoliation. Within the alternately-defoliated treatment these trends were repeated. This suggests the stimulus in grape vines for flower initiation is primarily located in the leaf subtending the axillary bud. An application of ethephon as 'Ethrel' (500 ppm a.i.) was made to the first 10 node length of actively-growing shoots. The effect on vegetative and fruiting characteristics was to be investigated the following season. Unfortunately the treatment destroyed most of the buds. Those buds that did grow the following spring did so at a slower rate than non-treated buds