Effect of exogenous gibberellic acid and presence or absence of testa on the ex vitro seedling growth of bay laurel (Laurus nobilis L.)

Abstract

Seed germination, seedling growth and viability are the initial, critical steps and they are affected by various exogenous and endogenous factors including seed testa and plant growth regulators. This study investigated the effects of testa (seeds with or without testa) and gibberellic acid (GA3; 0, 100, 500, 1000, 2000, 3000 and 4000 ppm) on seed germination, seedling growth parameters and seedling viability rate in bay laurel (Laurus nobilis L.). It has been definitely demonstrated that the seed testa extends seedling formation process at the final germination by nearly two times via delaying effects on the first germination time. For seed-with testa, all GA3 concentrations were found to be similarly successful (between 83.3 and 88.3%) compared to control (68.3%) but in seed-without testa, high GA3 concentrations (55.0% in 2000 ppm, 56.7% in 3000 ppm and 55.0% in 4000 ppm) showed greater negative effect on final germination than lower doses (80% in 100 ppm, 81.7% in 500 and 1000 ppm) and even control (63.3%). GA3 concentrations showed no differences in most seedling parameters excluding root number in seeds with testa and maximum root length in seeds without testa. Despite the delaying effect of testa, seedling and viability capacity were higher than those of seeds without testa in high GA3 concentrations. On the other hand, in control and lower doses of GA3 (100, 200 and 500 ppm) gave similar results of these two parameters. All data confirmed that Laurus nobilis L. seed testa have effects on seed germination delaying but found more resistant to seedling capacity (83.09%) and seedling viability (94.39%) in average after acclimatization in which seed-without testa gave lower results with 67.63%; 78.24% respectively in the ex vitro studies.