Effect of Growth Regulators (Abscisic Acid, Gibberellin, Salicylic Acid and Fluridone) and decapitation on increasing of leaf area and stevioside in Stevia

Tavakoli Hasanaklou, Nasibeh (2020) Effect of Growth Regulators (Abscisic Acid, Gibberellin, Salicylic Acid and Fluridone) and decapitation on increasing of leaf area and stevioside in Stevia. Doctoral thesis, University of Mohaghegh Ardabili.

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Abstract

Research Aim: In this study, in order to investigate the effect of growth regulators and decapitation treatment on increasing the branching ability and stevia sweeteners, three separate greenhouse experiments were studied. The aim of this study was to increase dry weight and the amount of steviol glycosides of stevia. Research method: According to the purpose of the study, three separate experiments were designed and carried out. The first experimental treatment was decapitation (decapitation and non-decapitation), abscisic acid (0, 50, 100 and 150 μM) and fluridone (0, 50, 100 and 150 μM) as well as the interactions of the treatments. The factorial experiment was conducted as a completely randomized design. In the second experiment, the treatments were decapitation, gibberellic acid (0 and 300 μM) and salicylic acid (0 and 300 μM). The third experiment included the best treatments of the two previous experiments. The aim of this study was to increase branching and leaf number, and also improve the production of sweeteners. The treatments included decapitation, abscisic acid, gibberellic acid, fluridone and their interaction. The concentrations of gibberellic acid were 0 and 300 μM and the concentrations of abscisic acid and fluridone were 0 and 50 μM each. Findings: The results of the first experiment showed that the leaf, stems and total dry weight were increased due to the application of fluridone up to 50 μM and abscisic acid up to100 μM. The interaction of abscisic acid up to 50 μM and fluridone up to 50 μM in non-decapitated plants had an increasing effect on the number of developed lateral buds and the number of branches. In this experiment, it was observed that the highest yield of steviol glycosides and the yield of rebaudiosids A were obtained by application of fluoridone up to 50 μM + abscisic acid up to 100 μM in decapitated plants. Based on the results of the second experiment, the highest amount of steviol glycosides and the highest amount of leaf dry weight were observed in decapitated plants and application of gibberellic acid. The highest concentration of soluble sugars, glucose and fructose were observed due to salicylic acid and gibberellic acid. Application of the interaction of salicylic acid and gibberellic acid in non-decapitated plants had the highest concentration of sucrose. Application of fluridone and gibberellic acid in decapitated plants increased leaf, stem and total dry weight, number of leaves, height and branches in the third experiment. The highest levels of abscisic acid were related to abscisic acid treatment in non-decapitated plants, while the concentration of endogen auxin decreased due to non-decapitation. Decreasing of these hormones may have been effective in increasing the branches. The highest concentration of stevioside and dulcoside A was due to the interaction of fluridone + abscisic acid + gibberellic acid. The highest levels of rebaudioside A, rebaudioside B and rebaudioside C were related to the use of fluridone + abscisic acid in capitated plants. While the highest yield of steviol glycosides was observed due to the use of fluridone + gibberellic acid + abscisic acid in decapitated plants Conclusion: In the first experiment, it was observed that the highest yield of steviol glycosides and the yield of rebaudioside A was obtained due to the application of 50 μM fluridone + 100 μM abscisic acid in decapitated plants. In the second experiment, the highest amount of dry weight, steviol glycosides and yield of steviol glycosides were observed in plants treated with gibberellic acid. Therefore, in the third experiment, gibberellic acid was used along with the best treatments of the first experiment. The results of the third experiment show that the application of fluridone and gibberellic acid can increase the biomass and yield of rebaudioside A in stevia. While the highest yield of steviol glycosides was observed due to fluridone + gibberellic acid + abscisic acid.

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