Biochemical regulation of apple fruit russeting: Phenolic dynamics, antioxidant activity and the role of growth regulators

Abstract:

Fruit russeting is a major physiological disorder that adversely affects the external appearance and market acceptability of apple (Malus domestica Borkh.) fruits. The present investigation elucidates the biochemical regulation of russet development with particular emphasis on phenolic metabolism and antioxidant activity under the influence of different plant growth regulators. Two russet-susceptible apple cultivars, Red Velox and Golden Clone-B, were evaluated across successive stages of fruit development. Total phenols, flavonoids, flavonols and total antioxidant activity were quantified at five critical developmental stages. The results demonstrated a pronounced stage-dependent activation of phenylpropanoid metabolism during early fruit development, followed by a progressive decline toward harvest, whereas antioxidant activity increased consistently with fruit maturation. Treatments involving GA₄₊₇ + 6-BA at optimal concentrations moderated early phenolic accumulation and were consistently associated with reduced russet expression, while higher concentrations of chlorogenic acid intensified phenolic accumulation and russet severity. Correlation analysis revealed a negative relationship between phenolic constituents and antioxidant activity at harvest, indicating a metabolic shift from structural reinforcement toward oxidative balance during fruit maturation. The study establishes a biochemical framework for russet development and provides a scientific basis for its management in apple.