Abstract

The role of salicylic acid (SA) and gibberellic acid (GA₃) pre-soaking were examined on stevia(Stevia rebaudiana) seed germination under NaCl or NaHCO₃ stress. A set of seeds was pre-soaked in H₂O, another set of seeds in 0, 0.1, 0.5, 1.0, 5.0 and 10.0 mM SA and another set in 200 ppm GA₃ for 24 h. Seeds were then placed in Petri-dishes with 5 ml of 0, 50, 100, 200 and 300 mM NaCl or NaHCO₃. Under the highest salinity condition no germination was observed.Seed germination was 65% in H₂O, 0, 5 and 1 mM SA, 33% in 5 mM SA, 12, 5% in 10 mM SA, 90% in 200 ppm GA₃ 44% in 50 mM NaCl, 14% in 100 mM NaCl, 40% in 50 mM NaHCO₃, 11% in 100 mM NaHCO₃. The germination velocity was 10.50 in H₂O, 6.50 in 1 mM SA, 15.00 in 200 ppm GA₃, 7.00 in 50 mM NaCl, 1.50 in 100 mM NaCl, 5.00 in 50 mM NaHCO₃, 1.00 in 100 mM NaHCO₃. Seed germination and velocity in NaCl was higher than the corresponding ones in NaHCO_3. By pre-soaking in 0.5, 1.0 mM SA the seed germination was as much as in H₂O, while in 5.0, 10.0 mM SA they were less than in H₂O. By pre-soaking in all SA concentrations, the 50 or 100 mM NaCl and also in NaHCO₃, this resulted in the reduction of germination in all combinations, when compared to their respective one in only 50 or 100 mM NaCl. In all SA concentrations the velocity was lower than the corresponding one in H₂O.Highest velocity was observed in 200 ppm GA₃.

Key words: Stevia Stevia rebaudiana, seed germination, NaCl, NaHCO₃, salicylic acid (SA), gibberellic acid (GA₃).