Foliar Stimulants: A Sustainable Strategy for Enhancing Plant Resilience to Abiotic and Biotic Stresses

The increasing frequency of abiotic and biotic stresses, such as drought, salinity, high temperatures, and pathogen attacks, threatens global agricultural productivity and food security. To address this, applying stimulants through foliar sprays has become a promising, sustainable method to boost plant resistance and improve crop yields. This review discusses the mechanisms, applications, and effects of using foliar stimulants, including amino acids, humic substances, phytohormones, vitamins, micronutrients, and plant extracts. Foliar application allows rapid nutrient absorption through stomatal openings and the cuticle, resulting in systemic movement via both apoplastic and symplastic pathways. Once absorbed, these stimulants activate physiological and biochemical processes, including hormonal regulation, antioxidant enzyme activity, osmolyte production, and stress-related gene expression. These processes collectively help maintain chlorophyll levels, enhance photosynthesis, strengthen cellular structures, and increase resistance to environmental stresses. Under abiotic stress, foliar applications of seaweed extracts, salicylic acid, silicon, and melatonin help stabilize membranes, improve water use efficiency, and preserve chlorophyll pigments. In cases of biotic stress, foliar stimulants support defense signaling, inhibit pathogen growth, and reduce visible disease symptoms like necrosis, and wilting. The review highlights how foliar application of stimulants contributes to sustainable agriculture by providing an eco-friendly alternative to traditional agrochemicals, improving nutrient use efficiency, and increasing crop yields even under adverse conditions. Furthermore, this review summarizes the recent advances in foliar stimulant research, providing a comprehensive framework for understanding their diverse roles and offering new perspectives on their practical applications in sustainable crop management.