Intercellular space limitation and ripening-associated sugar changes are associated with watercore susceptibility in durian fruit

Watercore is a physiological disorder that reduces fruit quality in durian, yet its underlying mechanism remains poorly understood. This study compared the tolerant cultivar ‘Monthong’ (MT) and the susceptible cultivar ‘Chanee’ (CN) to identify structural, physiological, biochemical, and molecular traits associated with watercore development. CN developed watercore symptoms earlier and reached nearly 100% incidence at the overripe stage, whereas MT exhibited only mild symptoms. These differences were not associated with fruit maturity, transpiration, fruit surface water uptake, or vascular structure. Instead, CN exhibited higher specific gravity and lower intercellular gas content in both the whole fruit and central axis, indicating smaller intercellular air spaces. Ripening was accompanied by greater accumulation of glucose, fructose, and total sugars in the central axis of CN than in MT, although these changes were not consistently associated with the expression of DzSUC2 , DzN3 , or DzCWINV1 . Osmotically driven water uptake was evident following vacuum infiltration, whereas apoplastic soluble solids concentration did not differ between cultivars in healthy fruit. During watercore progression, only apoplastic fructose increased significantly with symptom severity. Membrane deterioration occurred only during advanced ripening. Collectively, these findings suggest that limited intercellular air space is the primary factor associated with watercore susceptibility, while ripening-associated changes in sugar composition may contribute to symptom development.