REST BREAKING AGENTS ON APPLE ENDODORMANCY RELEASE UNDER SOUTHERN URUGUAYAN CONDITIONS

Abstract

Apple (Malus domestica Borkh) commercial production in Uruguay is mainly located in the southern area (35°SL), where winter conditions not always satisfy chilling requirements for adequate sprouting. Limitations as poor budbreak percentage and extended flowering period are usually overcome with rest breaking agent sprays. In the present work, we evaluate the response of four apple cultivars ('Royal Gala', 'Granny Smith', 'Red Chief' and 'Fuji'); to four or five rest breaking product sprays in three moments, during 2005 and 2006. A factorial experiment with two factors, product per moment, was applied. The products applied were: hydrogen cyanamide (1.25%), paraffin mineral oil (3.0%), paraffin mineral refined oil (2.0%) in all cases; and hydrogen cyanamide (0.75%) + paraffin mineral oil (2.0%) combination on 'Red Chief' (2005 and 2006), 'R. Gala' and 'Fuji' (2006). The first application was performed considering 250 CU (UTAH model) registered from sensors located in the trees (first 15 days of August). Following applications were performed on the first and third week of September. Budbreak percentage on field conditions was evaluated weekly. Bud type (reproductive or vegetative), position (lateral or apical) and branch age were registered. In addition, shoot length was quantified. At harvest, flesh firmness, soluble solid and starch contents were measured. For most cases, 'moment × product' interaction and the main 'product' effect on bud break were not significant, while the main 'moment' effect had high significance. Treatments applied at the second and third moment showed a significant rise in budbreak percentage, regarding the control; while treatments applied at the first moment, had precocious budbreak. Hydrogen cyanamide applied alone or combined in 'Royal Gala', also accelerated fruit ripening.