Impact of On-Tree Storage and Genotype on Citrus Granulation: Physico-chemical Analysis

This research aims to establish a link between advanced fruit maturity during on-tree storage and granulation incidence across nine commercially cultivated citrus genotypes. The focus was on understanding how on-tree storage impacts the incidence and severity of granulation, ranging from its onset to severe damage. Fruits were harvested at their optimal stage and monitored at 20-day intervals for up to 60 days of on-tree storage. Observations were made regarding various physico-chemical and functional attributes throughout this period. As granulation advanced, not only the juice vesicles undergo morphological changes but also the overall physical and functional quality of the fruit altered. Among the studied citrus cultivars, ‘Minneola’ was notably affected, displaying a granulation percentage exceeding 50% with increasing severity during on-tree storage. Physico-chemical traits significantly declined in stage IV compared to stage I. Granulated fruits exhibited notably lower total flavonoid content (16.25 mg quercetin equivalent/100g). Ascorbic acid content and total antioxidant activity shared a strong negative correlation with the degree of granulation, while respiration rate was positively correlated. R software was used for non-hierarchical K‑medoids (partitioning around medoids [PAM]) clustering to categorize genotypes based on their susceptibility to granulation at different harvesting stages, resulting in four distinct groups. Extended on-tree storage exacerbates both the incidence and severity of granulation in susceptible citrus genotypes such as ‘Minneola,’ ‘Dancy’ tangerine, and sweet oranges, making it an unadvised practice. However, on-tree storage of citrus genotypes such as ‘Pummelo Red Flesh,’ ‘Pummelo White Flesh,’ ‘Duncan,’ and ‘Marsh Seedless’ can potentially extend the marketable period by up to 2 months with minimal incidence of granulation.