Auxin and Tryptophan Effectiveness in Attenuating the Adverse Impacts of Drought Stress on Peanut Plants

Drought is a critical global issue that causes significant losses in agriculture productivity and quality. So, it must be reducing its deleterious effect on plants by applying natural compounds such as amino acids or growth regulators. A pot experiment was carried out during the summer seasons of 2023, 2024 at greenhouse of National Research Centre Dokki, Egypt, to investigate the effects of L-tryptophan (25 and 50 mgL− 1) or indole acetic acid (IAA) (50 and 100 mgL− 1) as foliar spraying on peanut plants irrigated by 90% water field capacity (WFC) or undergone drought (60% WFC). Drought significantly decreased growth parameters of shoot system, photosynthetic pigments, endogenous indole acetic acid, seed yield, and its nutritive value. Meanwhile, significantly increased growth parameters of root system, osmolytes, activity of enzymatic antioxidants, and non-enzymatic antioxidant. All applied treatments significantly increased photosynthetic pigments, endogenous IAA, osmolytes, activity of enzymatic antioxidants, and non-enzymatic antioxidant, and this promotion is reflected on the quantity and quality of the yielded seeds (oil, protein, and carbohydrate contents) and non-enzymatic antioxidants. In addition, the correlation analysis revealed strong interrelationships among yield, physiological, biochemical, and antioxidant traits under drought stress, highlighting the pivotal role of tryptophan and its derivative IAA in improving plant performance. It could be concluded that the use of either tryptophan or IAA was found to have a significant impact on growth, yield quality, and quantity of peanut plants growing under drought stress. Tryptophan, particularly at 50 mgL− 1, was more effective than IAA in mitigating drought.