Esmaeil Fayaz; ALI SOROOSHZADEH; Ali Heidarzadeh
Abstract
Introduction
Oil rapeseed (Brassica napus L.) stands out as a precious oilseed plant cultivated globally, ranking as the third major source of oil production. The cultivation of this ...
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Introduction
Oil rapeseed (Brassica napus L.) stands out as a precious oilseed plant cultivated globally, ranking as the third major source of oil production. The cultivation of this plant is expanding due to its notable nutritional and economic advantages. However, the arid and semi-arid climate of Iran poses a challenge to rapeseed cultivation, particularly with the occurrence of water deficit stress towards the end of the season. Various strategies are employed to mitigate the adverse effects of drought stress and enhance plant tolerance. One effective method involves the application of biological stimulants, such as amino acids. These compounds can stimulate plant growth and development, under optimal conditions and stress. Amino acids play direct and indirect roles in physiological metabolism, facilitating nutrient exchange and structural activities. This includes the augmentation of photosynthetic pigment concentration, enhancement of photosynthesis rate, and increased protein synthesis, particularly under stress conditions. In consideration of the significance of oil and the role of rapeseed in oil production, along with the challenges posed by drought stress during the reproductive growth stages of rapeseed, this study was conducted to examine the impact of foliar application of amino acids on the physiological parameters of oil rapeseed under conditions of irrigation interruption 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 oil rapeseed 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 2022-2023 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 residual of 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
Physiological and biochemical traits were adversely impacted by water deficit stress, as evidenced by the withholding of irrigation. This stress condition significantly decreased various characteristics, including maximum photosystem efficiency, photosynthesis rate, stomatal conductance, transpiration rate, and levels of photosynthetic pigments. However, applying amino acids via foliar spray mitigated the adverse effects of drought stress. The results indicated that the photosynthesis rate, stomatal conductance, transpiration rate, intercellular CO2 concentration, intercellular CO2/ambient CO2 ratio, photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), and chlorophyll fluorescence parameters were significantly influenced by the interaction between drought stress and foliar application of amino acids. The results indicated that the foliar application of two grams of amino acids per liter significantly increased various physiological parameters compared to the control group. Specifically, it resulted in a 22% enhancement in the photosynthesis rate, an 80% improvement in stomatal conductance, a 30% elevation in transpiration rate, a 40% rise in chlorophyll b, and a 27% increase in carotenoid levels. Conversely, the foliar spraying of one gram of amino acids per liter yielded the highest levels of chlorophyll a and the maximum quantum efficiency of photosystem II. These values were 20% and 5.5%, respectively, different from those observed in the control group. Also, the highest grain yield was obtained under withholding irrigation from 50% flowering stage (1440 kg ha-1), withholding irrigation from 50% flowering stage (2346 kg ha-1) and full irrigation during the season (4514 kg ha-1) with foliar application of 2 grams of amino acid per liter.
Conclusion
Based on the findings, the most favourable impact of foliar application of amino acids on the investigated traits was observed at a concentration of two grams per liter of water. Notably, the enhancement of these traits has a direct correlation with seed yield. Consequently, considering the substantial influence of these traits on the improvement of seed yield (22.4% and 61.4% under full irrigation and irrigation interruption conditions, respectively), the recommendation is to employ foliar spraying of two grams of amino acids per liter. This application is suggested to enhance rapeseed's physiological and biochemical characteristic across all three irrigation regimes, including full irrigation and interruption of irrigation from the flowering and budding stages.
