Response of physiological and biochemical characteristics of oilseed rape Nima cultivar (Brassica napus L.) to foliar application of amino acids under drought stress conditions

Introduction Rapeseed is one of the most important oilseed plants is cultivated in most regions of the world. Drought stress hurts the growth, development, and productivity of plants. and Canola, like many crops, is affected by this stress. Amino acids are one of the most important primary metabolites in plant cells that perform structural, metabolic and transport functions in plants, and many physicochemical characteristics of plant cells, tissues and organs are affected by the presence of amino acids. Considering the importance of oilseed rape cultivation in Iran in oil production and the problems of water scarcity at the end of the growing season of this plant, this research was conducted to study the oil rapeseed biochemical traits and oil yield change under amino acid foliar spraying and drought stress at the end of the season. Materials and methods This experiment was carried out as a factorial design based on randomized complete blocks in the research farm of the Faculty of Agriculture of Tarbiat Modares University, during the 1401-02 growing season. The experimental treatments include irrigation regimes at three levels (full irrigation, withholding irrigation from 50% flowering stage, withholding irrigation from pod forming) and foliar spraying at five levels (no foliar spraying, zero foliar spraying (distilled water), one, two and three grams of amino acids per liter). leaf area index (by DELTA-T DEVICES made in England) and greenness index (by SPAD) were measured one week after the last foliar spraying. Total chlorophyll, anthocyanin, flavonoid, proline, and phenol were measured based on fresh plant samples in laboratory according to the protocol. At maturity, biological yield, oil content and oil yield were measured. Statistical calculations of analysis of variance and mean comparisons were performed using SAS 9.4 software. Results and discussion The results showed that the interaction of drought stress and foliar spraying significantly affected the percentage and yield of oil, total chlorophyll, anthocyanin, flavonoid, proline, total phenol, leaf area index, SPAD and biological performance. Drought stress caused a significant decrease in traits such as leaf area index, yield and oil percentage, biological yield and total chlorophyll content. However, foliar spraying of amino acids at different levels reduced the negative effect of drought stress on the investigated traits. The results showed that the interaction of drought stress and foliar spraying significantly affected leaf area index, SPAD, biological yield, oil percentage and yield, total chlorophyll, anthocyanin, flavonoid, proline and total phenol. The highest leaf area index (3.52), biological yield (25955 kg/ha) and oil content (43.3%) were achieved by full irrigation conditions and foliar spraying of two grams of amino acids per liter. Also, the highest amount of anthocyanin (0.093 µmol g-1FW), flavonoid (1.64 µmol g-1FW) and proline (238.2 µmol g-1FW) were obtained by foliar spraying two grams of amino acids per liter under withholding irrigation from the flowering stage. Also, applying two grams of amino acid per liter produced the highest yield of oil (1924.6 kg/ha). Conclusion According to the results of this research, the positive effect of foliar spraying of amino acids on biochemical traits and oil yield was obtained by foliar spraying of two grams of amino acids per liter in all three irrigation regimes (full irrigation, withholding irrigation from 50% flowering stage, withholding irrigation from pod forming). Therefore, foliar spraying of two grams of amino acid per liter is recommended to increase oil yield in oilseed rap cultivation.