Responses of Foreign GA3 Application on Seedling Growth of Castor Bean (Ricinus communis L.) under Salinity Stress Conditions.

Castor bean (Ricinus communis L.), a promising bioenergy crop, is readily planted in marginal lands like saline soils. A controlled experiment was conducted to explore the possibility of using gibberellic acid (GA₃) as a promoter for caster bean grown under NaCl conditions and to try to determine the most appropriate concentration of GA₃ for seedling growth. The seeds of salt-tolerant cultivar Zibi 5 were firstly soaked with 0, 200, 250, and 300 µM GA₃ for 12 h and then cultured with 1/2 Hoagland solution containing 0, 50, and 100 mM NaCl in pots filled with sand. Plant height, stem diameter, leaf area, dry mater of each organ, activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), soluble protein, and proline content in the leaves were examined. Plant height and stem diameter, SOD, and POD activity was significantly highest in the treatment of 250 µM GA₃ under salt concentration of 50 mM NaCl among all the testing days; protein content was highest when GA₃ concentration was 250 µM under 100 mM NaCl treatment. This indicated that caster bean seed soaking with 250 µM GA₃ could be the most suitable concentration for promoting seedling growth of caster bean, improving their stress resistance. [ABSTRACT FROM AUTHOR]