Author : Surasak Nilnond

Summary : Experiments were conducted on 'Cardinal' and 'Black Ribier' grapes (1) to determine the effects of various GA3 concentrations applied at the pre-full and post-bloom stages on various cluster and berry characters, anatomical and physio-chemical changes related to the growth and development of berries, and (2) to determine the economics of GA3 application. Cluster length in 'Cardinal' and "Black Ribier' was increased by GA3 applied at pre-bloom stage at concentrations from 0.5 to 2 ppm. It was not affected by GA3 when applied at full and post-bloom stages in 'Cardinal' but was increased in 'Black Ribier' by 5 ppm applied at full bloom and 50-100 ppm at post-bloom. The highest GA3 concentration applied at pre-loom (2 ppm) and full bloom (10 ppm) reduced the number of berries per cluster, induced more shot berries and cluster loosening resulting in lighter weight of cluster in both varieties. The number of berries and therefore the cluster weight was not however, significantly affected in 'Black Ribier'.