Document Type : Research Paper
Authors
1 Department of Agrotechnology, Faculty of Agriculture, University of Tarbiat Modares, Tehran, Iran
2 Tarbiat modares university
3 Ph.D of Agronomy, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran
Abstract
Rapeseed (Brassica napus L.) is one of the most valuable oilseed plants cultivated in the world. Cultivation of this plant as the third source of oil production is expanding due to its nutritional and economic advantages. However, due to Iran's arid and semi-arid climate, the cultivation of this plant is affected by water deficit stress at the end of the season. Various methods are used to reduce the adverse effects of drought stress and increase plant tolerance. One of these methods is using biological stimulants such as amino acids. These compounds are able to stimulate plant growth and development under optimal conditions and stress. Amino acids have a direct and indirect role in physiological metabolism, exchange, and structural activities, such as increasing the concentration of photosynthetic pigments and the rate of photosynthesis and protein synthesis under stress conditions. Considering the importance of oil production in the country and the important role of rapeseed in oil production, as well as the problems of water scarcity in the reproductive growth stages of rapeseed, this research was conducted to investigate the effect of foliar spraying of amino acids on the physiological parameters of rapeseed in the condition of interruption of irrigation at the end of the season.
Materials and methods
This experiment was conducted to investigate the effect of foliar spraying of amino acids on the physiological characteristics and chlorophyll fluorescence parameters and photosynthetic pigments of oilseed rape under withholding irrigation at the end of the season (reproductive growth stage) as factorial design based on randomized complete blocks with three replications in the research farm of the Faculty of Agriculture of Tarbiat Modares University, during the 1401-02 growing season. The investigated factors were three levels of irrigation (full irrigation during the season, withholding irrigation from 50% flowering stage, withholding irrigation from pod forming) and five levels of foliar spraying (no foliar spraying, zero foliar spraying (distilled water), one, two and three grams of amino acids per liter) in stem elongation, flower-bud emergence, and flowering stages. The experimental plots included four planting rows and three meters in length. In the field, one week after the last foliar spraying, photosynthetic and transpiration rates and various fluorescence parameters were measured using a portable gas exchange and Mini-PAM device, respectively. Moreover, pigments (including chlorophyll a, b and carotenoid) in the fresh plant samples were determined in the laboratory. After ensuring the normality of the data, statistical analysis was performed using SAS software (version 4.9.) to compare the average data. The LSD test was used at the five percent level.
Results
All physiological and biochemical traits were affected by water deficit stress (withholding irrigation), which caused a significant decrease in characteristics, such as maximum photosystem efficiency, photosynthesis rate, stomatal conductance, transpiration rate and photosynthetic pigments. However, foliar application of amino acids reduced the adverse effect of drought stress. The results showed photosynthesis rate, stomatal conductance, transpiration rate, intercellular CO2 concentration and Intercellular CO2/ambient CO2, photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids) and chlorophyll fluorescence parameters were significantly affected by the interaction of drought stress and foliar spraying of amino acid. The highest photosynthesis rate (12.27 μmol CO2 m-2 s-1), stomatal conductance (0.153 mol H2O m-2 s-1), transpiration rate (1.33 mmol H2O m-2 s-1), chlorophyll b (832 0.0 mg.g-1FW) and carotenoid (0.812 m mg.g-1FW) were obtained by the foliar treatment of two grams of amino acids per liter, while the chlorophyll a (2.03 mg.g-1FW) and Fv/Fm (0.832) were obtained by spraying with one gram of amino acids per liter.
Conclusion
According to the results, the most positive effect of the foliar application of amino acids on the studied traits was two grams per liter of water. On the other hand, improving these traits directly affects seed yield. Therefore, considering the direct effect of these traits in improving seed yield, foliar spraying of two grams of amino acids per liter is recommended to improve the physiological and biochemical characteristics of rapeseed in all three irrigation regimes (full irrigation, interruption of irrigation from the flowering and budding stage).
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