Document Type : Research Paper
Authors
1 Department of Horticultural, Damghan Branch, Islamic Azad University, Damghan, Iran
2 Department of Horticultural Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad,Iran
3 Production and Technology of Herbal Medicines Research Center, Damghan Branch, Islamic Azad University, Damghan, Iran
Abstract
Background and Objective: Limited research exists on the relationship between different root structures and the content of steviol glycosides in various genotypes of the Stevia plant (Stevia rebaudiana Bertoni) under varying levels of drought stress. This study aimed to assess the relationship between root characteristics and the content of Rebaudioside-A (Reb-A) and Stevioside (Stev) in two Stevia genotypes under drought stress.
Methodology: This study evaluated the relationship between root attributes, yield characteristics, and the content of Reb-A and Stev in two Stevia genotypes (Chinese and Indian) under hydroponic conditions. Seven drought levels (-2, -4, -6, -8, -10, and -12 bars using polyethylene glycol 6000) were applied in 2023. The experiment consisted of two completely randomized design trials with three replications each. To begin the experiment, pots filled with a 1:1 ratio of vermiculite and perlite were prepared, and three uniform seedlings were planted in early April. Throughout the growth period and the application of drought stress using Hoagland solution, all pots were initially irrigated with distilled water until the establishment of plants. Once plant establishment was ensured, drought treatments were administered by irrigating once every three days with 400 mL of Hoagland solution with varying osmotic potentials based on the designated treatments. After 65 days from planting, all plants were carefully removed from the pots, and their aboveground and underground parts were separated to measure the desired traits. Steviol glycosides were quantified using high-performance liquid chromatography (HPLC) with two C18 columns and a UV-Vis detector at a wavelength of 202 nm. Finally, the results pertaining to each genotype were analyzed and presented separately.
Results: The results indicated that both genotypes experienced significant reductions in yield and growth characteristics, including plant height, leaf number, leaf fresh weight, leaf yield, and total biomass yield, under drought stress conditions. Compared to the control, all mentioned traits decreased notably under stress. At the -12 bar level, the reduction in leaf yield traits was 59.84% and 87.9% in the Chinese and Indian genotypes, respectively, while total biomass yield decreased by 52.51% and 64.19%, respectively. The Indian genotype exhibited a higher average leaf yield at non-drought stress levels, whereas the Chinese genotype showed a higher yield at higher drought stress levels (beyond -8 bars). This suggests that the Chinese genotype displays greater tolerance in terms of leaf yield under higher stress levels compared to the Indian genotype. Root-related traits, including fresh and dry weight, volume, length, and density, showed the highest averages in the Chinese genotype at the -4 bar level and in the Indian genotype at the -2 bar level. In both genotypes, partial drought stress (-2 bars) resulted in increased average content of Stev when compared to the non-stress treatment, with the highest content of Reb-A and Stev observed at this stress level in both the Chinese and Indian genotypes (2.58% and 2.58%, respectively, and 7.8% and 5.96%, respectively). According to the stepwise regression results, root area, leaf fresh weight, and total biomass yield were identified as influential traits in increasing the combined content of Reb-A and Stev.
Conclusion: Based on the findings, severe drought stress resulted in a decline in growth and yield traits, root characteristics, and the content and yield of the combined Reb-A and Stev. The synthesis of these two glycosides as metabolites in Stevia plants peaked at the partial drought stress level (-2 bars), highlighting their pivotal role as influential metabolites in imparting stress tolerance. The Chinese genotype exhibited the highest resistance to drought stress, displaying superior yield and content of combined Reb-A and Stev compared to the Indian genotype in certain instances. Overall, this study illustrates that severe drought stress directly diminishes the yield and content of Reb-A and Stev in Stevia plants. In contrast, certain root-related and yield traits can serve as reliable indicators of drought tolerance in this plant.
Keywords
Main Subjects
)