Response of lisianthus (Eustoma grandiflorum [Raf.] Shinn) to applications of growth regulators

Lisianthus is an ornamental species very attractive because of the vast array of flower colours and long vase life. The use of growth regulators, such as gibberellic acid (GA₃) and benzylaminopurine (BAP) in lisianthus production is limited as there are only few reports indicating that gibberellins promote bolting of rosetted plants. The objective of this work was to determine the response of lisianthus to foliar applications of GA₃ and BAP, in order to produce cut flowers. Plants of lisianthus ABC F₁ Series 'Misty Blue' were transplanted into black polyethylene bags of 7-L capacity; the substrate was volcanic rock 2 to 3 mm in diameter. Irrigation was performed with nutrient solution (200 mL bag^‑1 during the first 15 days and 300 mL bag^‑1 thereafter). The treatments were 6 mg L^‑1 of GA₃, 6 mg L^‑1 of BAP, 6 mg L^‑1 of GA₃ + 6 mg L^‑1 of BAP, 10 mg L^‑1 of GA₃, and a control (water). Three foliar applications were performed at 7, 9 and 11 weeks after transplant. The experiment was set in a completely randomized design with eight replicates per treatment. The results showed that the plants sprayed with GA₃ had similar height as that of control plants. Plants sprayed with BAP and GA₃ + BAP exhibited a 21 to 26% decrease in height but greater stem diameter, and showed a 300 to 450% increase in the number of shoots per plant, respectively. BAP and GA₃ + BAP also promoted a higher growth index (>500%) and reduced the bent neck. Plants sprayed with GA₃ + BAP had lower nitrogen and phosphorus concentrations in the tissue compared to that of plants with other treatments. The applications of GA₃ and BAP at the tested concentrations did not affect the biomass of the plants or the number of flower buds. The applications of BAP and GA₃ + BAP promoted favourable characteristics in lisianthus for pot plant.