Seed Coat Degradation and Viability Loss in Pomegranate: The Hidden Cause of Aril Paleness Disorder

Pomegranate aril paleness (AP), a physiological disorder linked to climate change, causes pale, desiccated arils in otherwise healthy fruits, reducing marketability. To investigate the anatomical and physiological underpinnings of AP, this study examined four pomegranate cultivars exhibiting varying degrees of susceptibility: the resistant cultivar 'Damavand' ( DN ), the moderately affected cultivars 'Kashmar' ( KN and KW ), and the severely affected cultivar 'Torud' ( TW ). Seed viability was assessed using germination tests and tetrazolium staining, while structural abnormalities in the seed coat were assessed through histological analysis and scanning electron microscopy (SEM). The results revealed a strong association between AP severity and reduced germination rates, with germination rates ranging from 45% in the resistant cultivar ‘DN’ to just 4% in the severely affected cultivar ‘ TW’ . Interestingly, tetrazolium tests indicated that a large proportion of embryos remained viable despite severe AP symptoms, ranging from 67% in ‘ TW’ to 98% in ‘DN’ . Microscopic analyses further demonstrated substantial structural degradation in the seed coats of AP-affected cultivars, including blackened regions, tissue separation, and reduced cellular density in the inner seed coat layers. Taken together, the findings highlight that AP is associated with specific anatomical abnormalities in the seed coat and tegmen, which may underlie or exacerbate the physiological manifestations of the disorder.