Changes in Morphological Characteristics, Endogenous Hormones, Soluble Sugars, and Anthocyanin Content During Fruit Development in Eggplant (Solanum melongena L.)

Understanding the coordinated regulation of growth and metabolism during fruit development is essential for improving crop quality and harvest management. This study investigated changes in morphological traits, endogenous phytohormones, soluble sugars, anthocyanins, and water-soluble vitamins in eggplant (Solanum melongena L.) fruit from 3 to 15 days after anthesis (DAA). Fruit length, diameter, and fresh weight increased significantly, with fresh weight increasing 16.6-fold. Cellular analysis showed that fruit enlargement was driven predominantly by cell expansion. Total soluble sugars increased 2.8-fold, with glucose and fructose as the predominant sugars. Delphinidin-based anthocyanins increased sharply during mid-development (9–12 DAA) and then declined slightly, whereas water-soluble vitamins decreased progressively. Based on integrated data, fruit development was classified into three phases: early (3 DAA, initiation and defense), mid (6–9 DAA, rapid growth and pigmentation), and late (12–15 DAA, functional maturation). Notably, 15 DAA was identified as a critical candidate stage with maximum sugar content, high anthocyanin levels, and completed seed development, suggesting its utility as a potential indicator of optimal harvest timing under the present conditions. These results provide an integrated understanding of developmental and metabolic processes in eggplant fruit and offer practical insights for optimizing harvest strategies.