| چکیده انگلیسی مقاله |
Extended abstract Introduction: Stevia (Stevia rebaudiana Bert.) is an herbaceous perennial plant that belongs to the family of Asteraceae. Stevia is a self-incompatible herb and the resulting seed from this plant have the low germination ability. Steviol glycosides found in this plant are 250-300 times sweeter than sucrose and despite sweet flavor; they are not absorbed by the body. In general, the poor germination capacity of stevia seeds is a major impediment for its cultivation on a large-scale. Priming is one of the seed enhancement techniques that could be resulted in the increase of germination percent and germination rate under stress conditions. Therefore, the present study was conducted to evaluate the impact of priming with salicylic acid (SA), iron (Fe) and zinc (Zn) on some germination indices, seedling growth as well as the content of photosynthetic pigments in stevia under normal and drought stress conditions. Materials and methods: A factorial experiment using a completely randomized design was carried out in the Seed Science and Technology Laboratory of Agricultural College, Shahed University, in 2017. The studied factors included four levels of drought stress (0, –0.3, –0.6 and –0.9 MPa) and seven priming combinations with SA, Fe and Zn; non-primed seeds (dry seeds) were also considered as control. In this experiment, Fe and Zn were supplied from sources of iron (II) sulfate heptahydrate (FeSO4.7H2O, 0.5%) and Zinc sulfate heptahydrate (ZnSO4.7H2O, 0.5%) respectively. The traits examined in this research included germination percentage, radicle length, plumule length, seedling weight vigor index and the content of photosynthetic pigments and carotenoid. Results: The results of this experiment indicated the plumule length was more sensitive compared with the root length to drought stress. With increasing intensity of drought stress from 0 to – 0.9 MPa, the content of photosynthetic pigments in stevia was significantly decreased in all priming treatments, so that the lowest amounts of chlorophyll a, b and carotenoid were observed at the potential of – 0.9 MPa. priming with SA + Fe + Zn was found to be more effective than other treatments to improve the germination characteristics and the chlorophyll content of stevia under normal and drought stress conditions. At the highest level of drought stress, germination percentage, radicle length, plumule length, seedling vigor index and total chlorophyll content were increased by 55.7, 50.5, 74.3, 90.3 and 85.5% than control in the concurrent application of Fe, Zn, and SA. Conclusion: In general, seed priming by micronutrient elements (Fe and Zn) and salicylic acid, and particularly the integrated application of them could be recommended to increase the resistance of stevia to drought stress in germination phase. Highlights: Drought stress at germination stage has a significant effect on seedling growth and the content of photosynthetic pigments in stevia. Seed priming increases drought tolerance of stevia at germination stage. The integrated application of SA, Fe, and Zn is more effective than their separate application to alleviate the drought-induced damaging effects. |