In 14 to 16-year-old‘Campbell Early’grapevines, 5-chloroindazol-8-acetic acid (ethychlozate) and naphthaleneacetic acid (NAA) increased flower abscission 5 to 8 days after they were applied to the leaves on the shoot each at 50 to 200ppm at full bloom, although such effect varied with seasons considerably. Moreover, they caused wilting of the shoot tip and leaves beginning several hours after the treatment, from which the shoot recovered after 7 to 10 days. When ethychlozate and NAA were applied to the flower cluster at full bloom at 100 and 200ppm, they increased not only the flower abscission but also the set of small seedless berries (shot berries). Ethychlozate and NAA had no effect on the sugar content of the must, while tended to decrease the total acidity especially at high concentrations.
Transport of photosynthates in the vines was studied by feeding given leaves with 14CO2 1, 4 and 7 days after NAA application using 3-year-old potted vines. The total 14C exported from the fed leaf were markedly less in the vines with foliage application of NAA (foliage-treated vines) than with cluster application (cluster-treated vines) and without NAA application (control vines). 14C assimilated by theleaf 2 nodes above the flower cluster was transported mostly to the shoot tip and stem above the cluster (upper parts) and little to the trunk and stem below the cluster (lower parts) and the cluster in the control and cluster-treated vines. While, in the foliage-treated vines, a fairly high proportion of 14C was found in the lower parts.
After feeding the leaf just above the flower cluster, some proportion of 14C was transported to the cluster in all treatments. In the control vines, transport to the upper parts decreased while that to the cluster increased as the feeding time was delayed to 7 days after the treatment. In the cluster-treated vines, transport to the upper parts decreased, while those to the lower parts and flower cluster increased markedly after feeding 7 days after the treatment. On the contrary, in the foliage-treated vines, transport to the upper parts was small after earlier feedings, while after feeding 7 days after the treatment it increased markedly accompanied with a sudden decrease in that to the flower cluster.
From these results, transport of the photosynthates to the flower cluster was assumed to be involved in the berry abscission following NAA application.
