Enzyme activity of carbohydrate metabolism in own-rooted and grafted ‘BRS-Kampai’ peach trees

Medium vigour rootstocks optimize peach fruit development in subtropical climates by balancing carbohydrate partitioning through enhanced SOX and AI enzymatic activity. Peach cultivation in subtropical regions faces critical challenges related to excessive vegetative growth, low winter chilling accumulation, and susceptibility to late frosts. The use of suitable rootstocks is a fundamental strategy to mitigate these problems, although the physiological mechanisms involved in vigour control and assimilate partitioning still demand investigation. This study aimed to determine the influence of five clonal rootstocks and the own-rooted scion cultivar (without rootstock) on the dynamics of the source-sink relationship and the seasonal partitioning of carbohydrates in ‘BRS-Kampai’ peach trees. Analyses such as shoot growth (SG), relative growth rate of shoots (RGR), and fruit diameter (FD) were performed; as well as the activity of the enzymes sorbitol oxidase (SOX) and acid invertase (AI), and concentration of reducing sugars (RS). High vigour group (own-rooted ‘BRS-Kampai’ and te ‘Okinawa’ rootstock) prioritises the diversion of assimilates to vegetative growth, resulting in smaller-sized fruits. In contrast, low vigour rootstocks (‘Cadaman®’ and ‘Clone 15’), although facilitating high-density management, present a delay in SG that induces direct competition with the initial phase of fruit development (cell division). The most efficient physiological balance was observed in medium vigour rootstocks (‘Tsukuba-2’ and ‘Tsukuba-3’), which showed the highest enzymatic activity (SOX and AI) in the fruits, indicating a superior sink strength in organs of economic interest. It is concluded that medium vigour optimises carbon partitioning to the fruits, consolidating the activity of both evaluated enzymes as a reliable marker of sink strength in peach trees under subtropical conditions.