Redox Dynamics Modulate Vascular Tissue Reconnection and Early Growth after Grafting in Pyrus andCydonia

Graft success depends on coordinated vascular tissue regeneration to restore scion growth. Reactive oxygen species (ROS), particularly hydrogen peroxide (H₂O₂), are involved in wound signalling, yet their role in controlling intergeneric graft compatibility remains unclear. This study evaluated early growth, redox metabolism and vascular reconnection in intergeneric grafts between quince (Cydonia oblonga) and pear (Pyrus spp.). A completely randomised 2 × 8 factorial scheme was adopted, comprising two rootstocks (Pyrus calleryana and Chaenomeles sinensis) and eight scion genotypes. Sprouting percentage, shoot length and diameter, hydrogen peroxide (H₂O₂) concentration, malondialdehyde (MDA) content and anatomical reconnection were assessed up to 120 days after grafting. Compatible combination exhibited markedly higher sprouting and shoot growth; for instance, ‘Triunfo’ reached 100% sprouting on P. calleryana, whereas P. calleryana on C. sinensis failed completely (0%), and C. sinensis on P. calleryana showed only about 10% sprouting. Callus formation was detected as early as 5 days after grafting (DAG), and continuous vascular connections were established by 25 DAG in compatible grafts, while incompatible combinations developed necrotic barriers at the graft interface. H₂O₂ concentration in the graft region ranged from approximately 261 to 579 nmol g⁻¹ FW and was generally higher in scion tissues, whereas MDA accumulation was greater in rootstocks, reaching up to around 560 µmol MDA g⁻¹ FW. Although single point oxidative markers did not strictly discriminate compatible from incompatible combinations, tissue-specific redox patterns and their timing were consistently associated with the speed of vascular reconnection and early scion growth. These findings demonstrate that ROS function not only as stress markers but also as developmental signals during graft healing, and suggest early vascular reconnection together with scion H₂O₂ and rootstock MDA as promising indicators of graft performance in woody species.