Physiological perspective of plant growth regulators in flowering, fruit setting and ripening process in citrus

Citrus is one of the most widely grown fruits worldwide, cultivated in over 130 countries, primarily in tropical and subtropical climates. Implementing successful and dependable breeding programs is crucial for addressing rising demands for adequate fruit performance and productivity. Our understanding of plant reproductive biology has advanced significantly in recent years, attributable to research on model plants. However, knowledge gained from these species cannot always be applied to citrus, owing to the fact that citrus is a perennial tree crop with distinctive reproductive biology. The growth and development of citrus fruits is a complex process impacted by a range of internal and external stimuli that could operate sequentially or concurrently. In the field of citriculture, plant growth regulators have become a crucial facet in increasing productivity by improving fruit sets and flowering. Plant growth-regulatory compounds actively regulate growth and development by controlling endogenous processes and altering the growth response exogenously. Different PGRs are also employed to expedite maturity, delay harvest, and retain fruit quality after harvest. The current review compiled comprehensive, up-to-date information on the role of plant growth regulators in flowering and fruit set during various stages of growth and development, as well as the ripening process in citrus, by bringing together the scientific and technical literature published on the PGRs subject with a focus on physiology and advancement in molecular biology from the beginning to till date. It will ultimately provide valuable information to researchers, particularly those involved in horticulture research, particularly fruit tree genetics and breeding.