Aril paleness disorder in pomegranate (Punica granatum L.): Etiology, effective mechanisms, and integrated management strategies

Aril Paleness Disorder (APD) is an emerging physiological abnormality that severely impacts the internal quality, market value, and antioxidant potential of pomegranate fruit. This disorder, characterized by significant reduction of red pigments in arils, results from complex interactions among genetic, physiological, environmental, and nutritional factors. Recently, APD has emerged as a critical global issue, particularly in Iran, the primary center of pomegranate origin and genetic diversity. This review integrates recent advances in the understanding and management of APD, with particular emphasis on insights emerging from molecular and biochemical investigations. Key factors influencing APD include cultivar-specific susceptibility, reduced expression of anthocyanin biosynthesis genes, deficiencies in essential mineral nutrients such as calcium, potassium, iron, and zinc, and exposure to environmental stresses including elevated temperatures. Contrary to earlier hypotheses, emerging evidence indicates that oxidative stress and anthocyanin degradation are likely secondary consequences of the disorder, and that disruptions in anthocyanin biosynthesis represent the more probable underlying mechanism. The key biochemical event is the failure in arginine metabolism and the subsequent flux of amino acids toward the phenylpropanoid pathway. Molecular evidence points to a defect in either the biosynthesis of anthocyanidins (the aglycone form) or their glycosylation into stable anthocyanins (the glycosylated form), highlighting the suppression of anthocyanin synthase (OXKF) and UDP-glucose flavonoid 3-O-glucosyltransferase ( UFGT ) genes. Effective management of this disorder requires an integrated approach combining tolerant cultivar selection, optimal foliar nutrition (especially calcium combined with iron, zinc, and silicon), canopy management to reduce heat stress, and regular irrigation regime. This review examines current knowledge from various perspectives, highlights existing gaps in disorder identification, and suggests future research directions.