| چکیده انگلیسی مقاله |
Background and objectives: Drought is one of the most important factors limiting the production of crops in the world, which can adversely affect the growth and performance of plants. Bacterial endophytes, as one of the microorganisms symbiotic with plants, play an essential role in improving the growth and performance of their host plants under drought-stress conditions. Considering the problems of water scarcity in Iran, this study was conducted to investigate the effect of the bacterial endophyte Agrobacterium deltaense isolated from the bitter myrtle (Salvia mirzayanii) plant on some quantitative and qualitative characteristics of thyme plants under drought stress.
Methodology: The bacterial endophyte was identified using morphological, physiological and molecular methods. Then, the sterilized Thyme seeds were cultivated under standard conditions and transferred to pots after two months. Six months after transplanting the culture to the pot, Thyme plants were inoculated in three stages weekly using A. deltaense bacterial endophyte. The bacterial suspension was adjusted in an NB culture medium with a 1 × 108 ml concentration. Then, they were applied as foliar spraying to the aerial parts of the plants and injected into the roots. To ensure the presence of endophytes after one month of foliar spraying to the aerial parts and injection to the roots, the bacterial endophyte establishment test was performed in the plant, and then drought stress was applied for three months, and then the morphological traits, Physiological and biochemical properties of thyme plant were evaluated. A factorial experiment in the form of a randomized complete design was performed in three replications on the research greenhouse of the Horticulture Department of Hormozgan University in 2021. The treatments were determined at four levels of drought stress (0, 25, 50 and 75% of field capacity) and two levels of bacterial inoculation (no inoculation and inoculation with A. deltaense). The assessed traits included: height, fresh and dry weight of stem and root, percentage of electrolyte leakage, chlorophyll a and b, total chlorophyll, carotenoid, prolin, soluble sugar, Total Phenolic Content, Essential Oil Percentage and mycorrhizal dependency.
Results: Drought stress led to significant effects on the reduced performance of garden thyme plants, including decreased stem height, fresh and dry weight of stems and roots, chlorophyll a and b, total chlorophyll, and carotenoids. However, under severe drought stress (75% field capacity), inoculation of garden thyme with the endophytic bacterium A. deltaense resulted in a significant increase in stem height (41.35%), root dry weight (71.85%), root fresh weight (74.35%), stem dry weight (83.22%), stem fresh weight (37%), chlorophyll a (97.15%), chlorophyll b (09.41%), total chlorophyll (77.20%), carotenoids (25%), and caused a significant reduction in electrolyte leakage by 90.5% compared to the control. Furthermore, the presence of the endophytic bacterium A. deltaense, in contrast to its absence under drought stress conditions, led to an increase in proline (17.07%), soluble sugars (15.09%), total phenolics (27.39%), and essential oil percentage (20%), mycorrhizal dependency (84%) compared to the control.
Conclusion: The study's results suggest that beneficial microorganisms, including bacterial endophytes, can be used as a suitable way to increase plant resistance to drought. This potential can be used for sustainable agriculture and reduced slaughter limits in dry and low-water areas. In the case of the use of A. deltaense bacterial endophyte in garden aviation slaughter under dry conditions, improvement in the growth and functioning of plants can be observed, as well as an increase in the percentage of essential oil and phenol content, which is an indicator of their quality and effective therapeutic compounds. This increase not only helps promote plants' medicinal properties but also increases their economic and commercial value. |