METABOLIC AND BURSTING RESPONSES OF APPLE BUDS TO BUDBREAKING PROMOTERS

Abstract

Apple (Malus domestica, Borkh) phenological responses to budbreaking promoters (BBP) application have been widely documented.
Nevertheless, there is scarce information on the metabolic activity induced by BBP. In this work, the metabolic and budbreak responses
of cv. Golden Delicious short flower limbs to hydrogen cyanamide (HCN) and thidiazuron (TDZ), applied 45 days before normal budbreak, were characterized. In the laboratory the metabolic activity (q) and respiration rate (RCO₂) of apical flower buds were measured by isothermal calorimetry, while under field conditions both lateral and apical flower buds responses were estimated by monitoring budbreak. In lab conditions, the application of HCN at 10, 15 and 20 mL L^-1 increased q of treated buds by 19.6 %, 15 days after application, as compared to controls, and with 15 mL L^-1 the RCO₂ of apical buds was increased by 16.6 %. Under field conditions and 30 days after application, HCN at 20 mL L^-1 produced 96 % and 67 % of apical and lateral budbreak, respectively; these values represented gains of 2.7 and 2.2 times over controls. With TDZ at 0.7 mL L^-1 there was a small but significant increase of 5.6 % in q, 15 days after application, but no change in RCO₂. However, 30 days after application under field conditions, TDZ at 0.7 mL L^-1 promoted both apical and lateral budbreak, since they reached values of 96 and 67 % respectively, which were 23 and 31 % higher than controls.