1973 Volume 42 Issue 2 Pages 131-137
The degree of competition for stored reserve substances and their utilization during flowering and berry setting periods in one-year-old grape vines were examined. The uppermost bud on each cutting was allowed to remain and others were cut off. Each experimental plant bore a single inflorescence on a woody cane. Plants were grown in a glasshouse in full sunlight during spring.
1 To assess the relative effectiveness of leaves, their position and time of defoliation on berry set, experiments were conducted with Campbell Early grape cuttings whose original weight was 15g. To assess the time of leaf removal on set, leaves were removed at three intervals: at bud break, 15 to 10 days before bloom, and full bloom. The manner in which leaf removal was accomplished was:(1) several leaves basal to a single flower cluster were left while the distal ones were removed (basal lot), (2) all leaves basal to flower cluster were removed and the distal leaves left intact (distal lot), (3) all leaves were removed (complete defoliation lot), and (4) all leaves were left intact (control lot). The average percent of fruited plants per treatment three weeks after full bloom was highest in the basal lot (42.2%). The effectiveness decreased in the following order: complete defoliated lot (24.5%), control lot (5.6%) and distal lot (2.2%). The presence of leaves is evidently not a prerequisite for berry set, although all berries in complete defoliated lot were shed before harvest time. This behavior suggests that the presence of leaves is evidently important for berry enlargement. Furthermore, the effects of leaf number and leaf position to flower cluster on berry set were examined. The presence of only 1 or 2 leaves basal to flower cluster was sufficient to obtain 40-60% of fruited plants. With increased number of leaves distal to flower cluster, the number of fruited vines decreased, which suggests that the competition for reserve substances and photosynthates during the critical period after anthesis may be an important factor for the fruit set and subsequent development.
These experiments emphasize the interaction between vegetative growth and development of reproductive organs on utilization of the reserve substances in grape. The poor fruit set in cuttings in which expanding immature leaves were left above flower cluster is probably attributable to the diversion of reserve substances and photosynthates neccessary for setting and subsequent development.
2 In experiments with the cv. Delaware whose original cutting weight was 15g, the effects of defoliation and pinching of shoot and pruning of the tip of young inflorescences on subsequent flower and ovary development were investigated. Defoliation resulted in good flowering response and development of ovary while pinching and tip pruning of inflorescences had none. Ovary development for one week after bloom was enhanced by leaf removal as compared to the control vines in which ovary growth was reduced by the presence of immature leaves. Although the fruitlets on cuttings from which all leaves were removed was twice that of intact cuttings, they abscised prematurely. When 1 or 2 leaves were left at a node below the flower cluster, 20-30% of the treated plants fruited.