CPPU and GA3 effects on pre- and post-harvest quality of seedless and seeded grapes

Berry size of seedless grapes is generally increased by application of GA(3) sprays at the time of fruit set. For certain cultivars a number of applications is required to obtain a commercially acceptable sized berry, and this may have deleterious effects on fruit bud initiation for the following year. It has been found that a similar increase in berry size can be obtained by a single application of CPPU to Perlette, Superior and Thompson Seedless cultivars As with GA(3), fruit ripening and maturation were delayed following CPPU application, sometimes even more severely than with GA(3). However, other aspects of development of the cluster were affected differently by each growth regulator. Such aspects include the growth of the rachis and pedicels, berry shatter after harvest and susceptibility of the berry to fungal attack and decay. These differences may be attributed to the anatomical effects of the regulators, in that CPPU increased the number and density of cells, whereas GA(3) enhanced cellular expansion and decreased cell density. Each growth regulator also increased the size of seeded berries of cultivar Zeiny and fruit ripening and resistance to decay were similarly affected. When a combination of both compounds was applied, there were no additive effects on berry size, berry firmness and fruit ripening, but the relative resistance to decay conferred by CPPU, was eliminated by addition of GA(3). Anatomical observations showed that the cell area and skin thickness of berries treated with both regulators were the same as for berries treated with GAR alone.