Effect of gibberellic acid application on growth and yield of artichokes under summer conditions

Globe artichoke (Cynara scolymus L.) is a perennial Mediterranean crop that is mostly harvested during the spring. The aim of this research was to determine the influence of GA(3) on the flower stalk growth and yield components of artichokes grown during the summer-autumn period. Field experiments were set up with the artichoke cv. Imperial Star at two locations: at Imotski (43 degrees 15'N, 17 degrees 14'E) in May 2002 and 2003, and at Split (43 degrees 30'N, 16 degrees 30'E) in May 2002, May 2003 and June 2003. Plants were treated once or twice with three concentrations of GA(3) (0, 15 or 30 mg.L-1) giving three combinations (0, 0+30 or 30+15 mg.L-1 GA(3)). At both locations in both years, higher flower stalks were observed in plants treated with 30+15 mg.L-1 GA(3) than in those treated with 0 or 0+30 mg.L-1 GA(3). Artichokes planted in May bolted from 82-100% after GA(3) application, while the percentage of the bolted plants from the June planting ranged from 0 for control plants to 45% when treated with 0 + 30 mg.L-1 GA(3), and 63% when treated with 30+15 mg.L-1 GA(3). Early yield (defined as the first three harvests) ranged from 0-4.6 t.ha(-1) and increased by GA(3) treatment. Plants sprayed with 30+15 mg.L-1 GA(3) produced higher early yields compared to plants that received the other treatments at both locations and in both years. The total yield of plants sprayed twice with GA(3) increased 20-100% as compared to the untreated plants. The application of GA(3) increased the number of heads (primary, secondary and total), while its impact on head weight was less pronounced. GA(3) application during the summer cultivation increased bolting and yield, especially under non-inductive conditions in the coastal area for the June planting.