Effects of Root Applications of Gibberellic Acid on Photosynthesis, Transpiration, and Growth of Geranium Plants

Four concentrations of GA 3 were applied to the root systems of 2 geranium ( Pelargonium × hortorum L.H. Bailey) cultivars grown hydroponically. The 0.014 μ m GA 3 treatment promoted substantial increases in relative growth rate (RGR) in both ‘Sincerity’ and ‘Glacier Crimson’ (Syn. ‘Brum’). A maximum stimulation in RGR was obtained at 0.14 μ m and 1.4 μ m GA 3 concentration in ‘Sincerity’ and ‘Glacier Crimson’, respectively. Transpiration rates in both cultivars exhibited a maximum decrease with the 1.4 μ m GA 3 treatment, whereas net photosynthetic rates and total chlorophyll were unaffected by GA 3 . The response to GA 3 also was evaluated for geraniums grown in a soil mix. There was a difference in cultivar responsiveness to root applications of GA 3 . Cutting production was greatest with 2.8 μ m GA 3 treatment and fresh weight, dry weight, and cutting length were greatest with a 28 μ m GA 3 concentration for ‘Sincerity’. The number of cuttings and length of cuttings were greatest with GA 3 at a 56 μ m GA 3 concentration, and fresh and dry weight were maximized with a 28μ m GA 3 concentration for ‘Glacier Crimson’.