Nitrate reductase activity and carbohydrate accumulation explain flowering responses of mango cultivars grafted onto contrasting rootstocks

Rootstock–scion interactions modulate nitrogen and carbon metabolism in Mangifera indica L. This study evaluated the temporal integration between nitrate reductase (NR) activity, total soluble carbohydrates (TSC), and flowering intensity in mango cultivars grafted onto contrasting rootstocks under semi-arid conditions. The experiment was conducted over two growing seasons in Petrolina, Brazil, using a randomised block design in a 3 × 4 factorial arrangement with three polyembryonic rootstocks and four scion cultivars. NR activity and TSC concentration were quantified in mature leaves at full flowering, and flowering intensity was expressed as the percentage of flowering branches. Rootstock × scion interactions significantly regulated NR activity and TSC accumulation, evidencing strong genetic and environmental modulation. A positive carry-over effect of NR activity on flowering was observed. Cultivar-specific physiological strategies were identified, with ‘Kent’ and ‘Keitt’ exhibiting greater metabolic efficiency, whereas ‘Palmer’ and ‘Tommy Atkins’ displayed more plastic responses.