The concentration effect of urea applied as an additive together with BA to the prebloom GA application on set and growth of seedless berries of Delaware grape was examined using 5 adults vines grown in a vinyl film house. The experiment was consisted of 9 treatments ; GA (100 ppm) alone, GA+urea at 0, 0.5, 1.0 and 1.5% combined with 2 levels (100 and 200 ppm) of BA. These treatments were conducted 11 days prior to full bloom by means of cluster dipping, and GA alone was applied at 100 ppm again to all the treated clusters 10 days after full bloom.
Berry weight measured 10 days after full bloom and urea concentration ran parallel with each other at both BA levels. Almost similar trend in berry weight was observed 9 days later, although the differences among treatments became a little smaller and the highest weight was gained at the urea level of 1.0% in the series of BA 200ppm. The enhanced berry growth caused by these treatments mainly depended on the rapid cell growth in size of inner wall.
No significant differences of berry weight, however, were detected among these treatments at the harvest time, 66 days after full bloom. On the other hand, berry number per cluster and cluster weight were significantly increased by the combined applications of urea at 1.5% with BA 100ppm, and at the levels higher than 0.5% with BA 200 ppm. Any treatments did not affect skin color and the contents of sugar and acid in juice.