EFFECT OF THIDIAZURON CONCENTRATION AND APPLICATION PERIOD ON ‘ROYAL GALA’ APPLE FRUITING AND PRODUCTION

ABSTRACT ‘Gala’ apple trees have low fruit set in restrictive pollination situations, being an obstacle to the achievement of high production rates in orchards in southern Brazil, which can be minimized by the use of growth regulators. The aim of this study was to evaluate the effect of thidiazuron concentrations in ‘Royal Gala’ apple fruiting and production, grown in mild winter conditions. The experiment was conducted during the 2011/2012, 2012/2013 and 2013/2014 crop years in Fraiburgo, SC, on ‘Royal Gala’ apple trees in Marubakaido rootstock M9 with filter. In all evaluation cycles, the experimental design was a randomized block with factorial arrangement (6x2) with six TDZ concentrations and two application forms, with six replicates, and the experimental unit consisting of one plant. The TDZ concentrations of each treatment were applied split into two seasons. The first application was performed on pink bud stage (E2) and the second application was in full bloom stage (F2). The variables evaluated were: fruit set (%), return bloom (%), number and weight of fruits per plant, mean fruit weight (g) and average number of seeds per fruit. Data were submitted to analysis of variance, in which for significant variables by the F test, analysis of contrast and polynomial regression were performed in order to evaluate the response of variables with increasing TDZ concentration. TDZ is effective even at low concentrations, increasing the production and fruit set of ‘Gala’ apples in the climatic conditions of southern Brazil.