Atefeh Amini Neisiani; Abbas Saidi; Masoud Tohidfar
Abstract
IntroductionStevia rebaudiana Bertoni is a medicinal plant commercially used as a non-caloric sweetener for diabetic patients. Stevia seeds are small and infertile, and exhibit a relatively ...
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IntroductionStevia rebaudiana Bertoni is a medicinal plant commercially used as a non-caloric sweetener for diabetic patients. Stevia seeds are small and infertile, and exhibit a relatively low germination rate. Moreover, given the steviol glycoside content and morphological characteristics (such as leaf shape and color), cross-pollination in this plant, leads to a great deal of diversity among the plants grown from the seeds. Consequently, asexual propagation methods are vital for the effective cultivation of this plant. Micropropagation not only enhances growth and reproduction rates, it also preserves genetic resources. Furthermore, it allows for the creation of a genetically homogeneous population with high yields of steviol glycosides, which makes it a suitable method for the propagation of Stevia. The present study aims to evaluate the effects of various growth regulators on this plant, presenting an efficient protocol for commercial cultivation.Materials and MethodsStevia seed germination rates were calculated on MS medium at four and eight days post-sowing. Shoot induction was examined using combinations of kinetin (KIN), gibberellic acid (GA3), and benzylaminopurine (BAP). Subsequently, rooting experiments were conducted with three auxin hormones: naphthaleneacetic acid (NAA), indole-3-acetic acid (IAA), and indole-3-butyric acid (IBA). The acclimatization of the samples was conducted following successful rooting.Results and DiscussionThe germination rate of Stevia seeds was found to be 33.38%. The best shoot proliferation was achieved with 0.5 mg/L BAP and 2 mg/L KIN, producing the highest number of leaves and lateral branches. Optimal fresh weight (437.29 g) and shoot length (15.38 cm) were obtained in the treatment with 1.5 mg/L GA3 and 2 mg/L KIN. Significant negative correlations were observed at the 1% probability level between leaf number and shoot length (-0.61**), leaf number and fresh weight (-0.46**), lateral branch number and shoot length (-0.81**), and lateral branch number and fresh weight (-0.69**). Significant positive correlations were found between leaf and lateral branch numbers (0.95**) and between shoot length and fresh weight (0.98**). The longest root was observed in the treatment with 0.5 mg/L NAA, and the highest number of roots was found in the treatment with 1 mg/L IBA. The study reveal the effectiveness of specific combinations of growth regulators for the micropropagation of Stevia rebaudiana. The findings indicate that the hormonal treatments significantly affect various growth parameters, including leaf number, shoot length, fresh weight, and root development. The negative correlations between some traits suggest that optimizing one growth parameter might compromise. The positive correlations between other traits, such as leaf and lateral branch number, suggest that some growth attributes can be simultaneously enhanced.ConclusionThe optimized protocol for the micropropagation of Stevia rebaudiana (0.5 mg/L BAP and 2 mg/L KIN for shoot proliferation, and 0.5 mg/L NAA for root induction) demonstrated efficient and economical performance using fewer and less diverse hormones compared to existing micropropagation protocols. Therefore, it can be considered an optimum protocol for the propagation of Stevia, potentially benefiting commercial cultivation and research applications.
