Hormonal, biochemical, and genetic regulations of walnut fruit development and ripening: an integrated perspective

Walnut (Juglans spp.) trees hold immense significance in both economic and ecological contexts within agri-horticultural ecosystems. The comprehension of the intricate mechanisms underpinning walnut growth and development stands as a pivotal endeavor, essential for advancing sustainable yield practices. This comprehensive review delves into the multifaceted factors that contribute to the growth and development of walnuts, encompassing hormonal, biochemical, and genetic dimensions. Notably, hormones such as gibberellic acids (GAs) and sugars assume pivotal roles in the initiation and maturation of walnut flowers, with specific investigations demonstrating that the application of GAs has the capacity to augment male flower counts. The levels of endogenous auxins and gibberellins exhibit variations across distinct phases of walnut development, with the highest concentrations observed in young tissues. The molecular underpinnings of walnut growth and development involve a complex interplay of genetic regulation, hormonal dynamics, and environmental factors. Distinct sets of genes exhibit activation at discrete developmental stages, thereby influencing fundamental processes such as cell division, differentiation, and food reserve metabolism. Several key regulatory genes, including ACC, ASMT, SAD, FAD, SOC, and TFL1, emerge as pivotal orchestrators, steering essential processes encompassing cell division, differentiation, flowering, and fruit development. Conclusively, this article provides a detailed exploration of the diverse aspects of walnut growth and development, from genetic regulation to hormonal and biochemical processes. This will provide a valuable resource for researchers, horticulturalists, and biotechnologists aiming to improve walnut productivity and resilience in the face of changing environmental conditions.