Document Type : Research Article
Authors
1 Department of Horticultural Science, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Ahvaz, Iran
2 Department of Biology, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran.
3 Department of Horticultural Sciences, Faculty of Agriculture, Ilam University, Ilam, Iran.
Abstract
Artemisia herba-alba is a silvery perennial shrub whose essential oil contains 1 and 8-cineole, chrysanthenon, chrysanthenol, thujone, and camphor. The therapeutic properties of the plant include antioxidant, antibacterial, antispasmodic, treatment of respiratory and digestive disorders, diabetes, disinfectant, vasodilator, insecticidal, anthelmintic, and nematicide. Nowdays, the wild population of this species has been severely reduced, and it is now considered as a rare and endangered plant. Cultivation or domestication of this medicinal species can be a promising alternative for its conservation and sustainable use. Physiological studies have proven that the seeds of A. herba-alba contain phytotoxic chemicals that prevent germination under adverse conditions.
To investigate the elimination of seed dormancy and enhance the germination of A. herba-alba seeds, different concentrations of potassium nitrate and gibberellic acid for two periods of time were studied. Moreover, the superior treatment was combined with light treatment at four levels. The first experiment was implemented as a factorial based on a completely randomized design with three replications in the laboratory of the Horticulture Department, Faculty of Agriculture, Shahid Chamran University, Ahvaz. The first factor included the gibberellic acid at three concentrations (250, 500, and 1000 ppm) and potassium nitrate at three concentrations (50, 100, and 200 mM) which were applied separately. The second factor included the duration of priming at two periods (12 and 24 hours). Based on the results of the first experiment, the second experiment was conducted with the superior treatment in the first experiment (500 ppm gibberellic acid for 12 hours) along with dry and wet chilling treatments as the first factor in combination with light treatment at four levels (0, 8, 16, and 24 h) as the second factor. At the end of the experiments, the length of the root, shoot, seedling height, fresh and dry weight, seed longitudinal and weight vigor index, germination percentage and rate, and alpha-amylase enzyme activity were measured. Statistical analysis of the measured traits was performed using SAS version 9.4 statistical software (SAS Institute Inc., Cary, NC, USA). The LSD test (P=0.05) was used to compare the means. Also, principal component analysis (PCA) and heat map correlation (HMC) were performed to identify the relationships between traits and the dispersion of treatments using the R studio v1.3.959 package.
The results showed that the gibberellic acid and potassium nitrate treatments had a significant effect on the studied traits at all levels, while the impact of priming duration treatment was not significant. Based on the findings of the first experiment, the highest shoot length (13 mm), root length (12 mm), seedling height (25 mm), fresh weight (0.0110 gr), seedling dry weight (0.0022 gr), longitudinal vigor index (1806.3), weight vigor index (0.1604), germination percentage (71%), germination rate (8.1 seed/day), and alpha-amylase enzyme activity (0.0676 mg/gFWmin-1) were recorded in the 500 ppm gibberellic acid treatment. The results of the second experiment showed that the combined treatment of 16 hours of light with the gibberellic acid was able to increase the longitudinal and weight vigor index of the seedling, percentage, speed, and activity of the alpha-amylase enzyme by 240.13%, 221.2%, 358.82%, 356.8%, and 60.78% compared to the control, respectively. The combined treatment of 16 hours of light with the gibberellic acid had the greatest effect on the dormancy breaking of A. herba-alba seeds (78% germination). The results of the heat map correlation (HMC) showed that there was a positive correlation between the traits of seedling height, root and shoot length, seedling fresh and dry weight, longitudinal and weight vigor index, speed, and percentage germination. Also, the alpha-amylase enzyme was positively correlated with the longitudinal and weight vigor index, speed, and germination percentage and negatively correlated with seedling height, root and shoot length, and seedling fresh and dry weight. In the first experiment, principal component analysis showed that the combination of the first two components explained 86.35% of the variations, which accordingly included 78.53% of the first component and 7.82% of the second component. Based on this analysis, seedling height, root, and shoot length, longitudinal and weight vigor index, speed, germination percentage, and alpha-amylase enzyme, which were the highest of these traits recorded in the treatments of gibberellic acid hormone and potassium nitrate, played a role in the loading of the first component. Also, in the second experiment, it was determined that the combination of the first three components explained 92.73% of the variations, which included 56.17% of the first component, 28.85% of the second component, and 7.71% of the third component. Based on this analysis, seedling height, root and shoot length, longitudinal and weight vigor index, and germination rate, which were the highest in the light treatment, played a role in the loading of the first component. Germination percentage and alpha-amylase enzyme, which were the highest in the combined light treatment with gibberellic acid, played a crucial role in the loading of the second component.
In this study, the results showed that A. herba-alba seeds are photoblastic positive, and since gibberellic acid is generally effective in breaking dormancy caused by metabolic barriers, it can be said that metabolic barriers mainly cause dormancy in the seeds. Therefore, in the light treatment (16 hours) and combination with gibberellic acid (500 ppm), the highest values of the longitudinal and weight vigor index traits of the seedling, the percentage and speed of germination, and the activity of the alpha-amylase enzyme were recorded. In the same treatment, germination increased nine days after the treatment, and the germination percentage increased from 20% in untreated seeds to 78% in primed seeds. Also, in the treatment of the gibberellic acid (500 ppm) alone, the highest shoot length, root length, seedling height, and fresh and dry weight were recorded. Therefore, light treatment (16 hours) combined with gibberellic acid (500 ppm) was introduced as the most effective strategy to increase seed germination of A. herba-alba and thus help save this species from extinction. The present study showed that the use of combined light treatment with gibberellic acid is a very effective and low-cost strategy to break seed dormancy and germinate A. herba-alba medicinal plant.
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