Gibberellic Acid Sensitivity among Common Bean Cultivars (Phaseolus vulgaris L.)

To lower seed yield loss from directly harvested common bean or dry bean, height of the lower pod-bearing nodes needs to be raised. The objective of this greenhouse study was to stimulate lower stem elongation by gibberellic acid (GA(3)) of dry bean cultivars. Seeds of cv. Matterhorn, erect indeterminate Type II, and cv. Poncho, prostate indeterminate Type III, were dipped in GA(3) at 62.5 to 16,000 ppm and planted. After 14 d, the height of the unifoliate and first trifoliate nodes showed maximum stimulation of stem elongation by 1000 ppm GA(3) for 'Poncho' and by 2000 ppm for 'Matterhorn'. Application of 1 mL of GA(3) at 0.031 to 2048 ppm to newly expanded unifoliate leaves showed cultivar differences. Whereas 'Matterhorn' was promoted at 64 ppm and reached a maximum height by 512 ppm GA(3), 'Poncho' was promoted at 0.25 ppm and reached a maximum height by 8 ppm GA(3). Flowering of 'Matterhorn' was unaffected by GA(3); flowering of 'Poncho' was completely inhibited by 128 ppm. The sensitivity difference of cultivars was verified with other cultivars. Type I cultivars, which are all determinate, showed a full range of GA(3) sensitivity. Dry bean cultivars may be regrouped based on the GA(3) dose to which they respond. Individual response to GA(3) rates of dry bean cultivars needs to be predetermined using a short-term, 2-3 weeks, greenhouse bioassay before field use of GA(3).