CHILLING WINTER AND ROOTSTOCKS INFLUENCE ON ROYAL GALA APPLE BUD BREAKING AND BLOOMING

Abstract

The apple tree (Malus sylvestris var. domestica) is grown in a wide variety of environments, with different rootstocks and cultivars; thus, the characterization of the response of the plant in each of the environmentcultivar- rootstock combinations is important to understand the tree behavior in its environment. In order to explore the influence ofwinter cold expressed in chill units (CU) accumulated during the winter period as well as rootstocks on bud breaking and blooming of apple trees, an apple orchard with the Royal Gala cultivar grafted on 12 different rootstocks was selected. During the winter periods of 2010-2011 and 2014-2015 CU were calculated and after that, the percentage of open buds and the day degrees (DD) required for the beggining (5 %) and during the flowering event (from 5 to 95 % ) for each of the environment-cultivar-rootstock combination were registered. The bud opening and blooming of Royal Gala were periodically measured in percentage of occurrence and related to CU, DD and rootstock. After a winter with low chill units accumulated (524 CU) there was 72.6 % of bud breaking, blooming began at 236 DD and was completed with 117 GDD, while after a winter with 830 CU there was 96.7 % of bud breaking, blooming began at 146 DD and was completed with 129 DD. Significant difference for winter cold factor was detected on bud breaking and DD accumulated at the beginning of blooming and statistical equality for the duration of blooming period. No significant effect of rootstocks or significant interaction between CU and rootstocks were detected.