Fruit firmness is a critical quality trait that influences both postharvest life and potential commercialization of fruits. In cranberry, fruit firmness is highly correlated with the efficiency of producing higher valuable products such as sweetened and dried cranberries (SDC). As in many fruit crops, cranberry firmness declines during ripening, a process often associated with enzymatic solubilization of cell wall polysaccharide. Calcium (Ca) plays a fundamental role in maintaining cell wall integrity by cross-linking with pectins to form calcium pectates, which strengthen the cell wall and limits its disassembly. The objective of this study was to determine changes in cell wall composition through fruit development in two cranberry cultivars with contrasting fruit firmness. Fruit samples were collected every two weeks from 14 to 91 days after full bloom (DAFB) from cranberry ‘Stevens’ and ‘BG’. External fruit quality traits–such as anthocyanin accumulation, fruit size, and weight– were measured alongside internal fruit quality parameters, including internal structure, cell wall composition, and calcium content. Before fruit color developed, both cultivars were similar in size and firmness; however, ‘Stevens’ had higher fruit elasticity compared to ‘BG’. This difference was attributed to lower pectin solubility in the cell walls of ‘Stevens’. As ripening progressed, notable differences in firmness emerged between the two cultivars, particularly between 84 and 91 DAFB. This divergence was associated with increased solubilization of pectins and hemicellulose. Additionally, solubilization of tightly bound hemicellulose was negatively correlated with Ca content in the fruit cell wall. Differences in cell wall-associated Ca content between cultivars were observed throughout fruit development and may explain the variation in firmness at harvest and after 30 days of storage. These findings suggest that cell wall-bound Ca is an important factor influencing fruit firmness and could serve as a valuable selection parameter in breeding programs. Moreover, understanding these differences may aid cranberry growers in in making informed cultivar selection decisions for their plantings.
