Gibberellins improve caper seeds germination: guidelines for their application

The caper is an important plant in the Mediterranean area, tolerant to drought, used for its flower buds and fruits, and recently for its bioactive principles. The seeds present a low germination percentage (G), which has been related to physiological dormancy because dormant seeds germinate in the presence of gibberellic acid (GA₃) solutions. The objective of this study was to provide practical guidelines for gibberellin use to improve G. Three experiments were carried out. In the first experiments, two GA₃ application methods (1 – wetting the germination substrate of the between-paper method with a GA₃ solution, and 2 – soaking the seeds in the GA₃) using five GA₃ concentrations (0, 100, 500, 1000 and 2000 mg L^‑1) were compared. The best result was obtained by wetting the substrate with the 500 mg L^‑1 GA₃ solution (76.3%). In the second experiment, different methods for wetting the substrate with a 500 mg L^‑1 GA₃ were compared. The method of continuous wetting, used in the first experiment, was compared with 1 – changing the germination substrate fortnightly, and 2 NDASH with wetting the substrate with the GA₃ solution for 30 days and with water afterwards. The best result was obtained by changing the substrate (86%) or wetting it with GA₃ only for 30 days (83%). In the last experiment, lower GA₃ and technical gibberellin (A₄ and A₃) concentrations were compared (0, 0.1, 1, 5, 10 and 50 mg L^‑1). A₄ led to higher G than control, even at the lowest concentration, and the best results were achieved from 5 mg L^‑1 without significant differences between concentrations (up to 92.3%). Overall to improve caper seed germination it is recommended to apply an A₄ solution at low concentrations (minimum 5 mg L^‑1) or to use a 500 mg L^‑1 GA₃ replacing the germination substrate fortnightly, or to apply such a solution for 30 days, and then continue to wet the substrate with water.