Abstract
The effects of exogenous gibberellin A3 and gibberellin synthesis inhibitors on the flowering time of the Japanese iris were investigated in open fields. Foliar applications of GA3 to the medium flowering cultivar ‘Chihayajo’ at a concentration of 250 ppm in mid-April forced the flowering of the first floret 4 days early. Uniconazole-P at a concentration of 25 ppm in early May delayed the flowering of the second floret by 7 days. Cultivar differences in the effects of GA3 and uniconazole-P on the flowering time were observed. A very early flowering cultivar ‘Yatugatake’ showed no difference in the average flowering day treatment while the medium flowering cultivar ‘Chihayajo’ showed the largest difference. These results suggest that sensitivity to GA3 differed depending on cultivar. Treatment with chlormequat-chloride was less effective in inhibiting scape elongation, while paclobutrazol and uniconazole-P were remarkably effective. However, the effect on flowering time did not always correspond with the inhibition of scape elongation. With 2000 ppm chlormequat-chloride treatment, the average flowering day of the second floret was delayed by 4 days compared with the control, similar to 500 ppm paclobutrazol treatment.
