Plant Growth Regulators in Horticulture: Physiological Mechanisms, Practical Applications, and Future Perspectives

Plant growth regulators (PGRs) are naturally occurring or synthetic bioactive compounds that modulate plant growth, development, and physiological processes at relatively low concentrations. In horticultural crops, PGRs play important roles in regulating vegetative growth, flowering, floral sex expression, fruit set, fruit retention, yield, produce quality, and postharvest longevity. Their physiological effects depend on several factors, including the type and concentration of the regulator, crop species, cultivar, plant developmental stage, application method, and prevailing environmental conditions. The judicious use of PGRs can improve reproductive performance, reduce premature fruit abscission, mitigate certain physiological disorders, and enhance the quality, shelf life, and marketability of horticultural produce. This review critically evaluates the physiological functions and potential applications of major groups of PGRs in fruit and vegetable crops and ornamental plants, with particular emphasis on their roles in vegetative growth regulation, reproductive development, yield improvement, quality enhancement, and postharvest management. It also highlights the importance of optimising regulator-specific concentrations, application timings, and methods of application while integrating PGR treatments with appropriate irrigation, nutrient management, and other recommended crop production practices. A comprehensive understanding of the physiological and biochemical mechanisms underlying PGR-mediated responses, together with the development of crop- and cultivar-specific application strategies, is essential for improving their efficacy and promoting sustainable, resource-efficient, and commercially viable horticultural production systems.