Dinâmica de dormência e resistência ao frio em macieiras cultivadas em região de inverno ameno no Brasil

Abstract

The production of temperate fruit trees is directly influenced by the quantity and quality of chilling accumulated during winter. When these fruit trees are cultivated in areas with winters that have low chilling accumulation, they exhibit heterogeneous budburst and flowering, resulting in reduced production potential. This condition has driven the relocation of cultivation to higher altitude zones or encouraged the development of genotypes with low chilling requirements. Both strategies expose the crops to the risk of frost damage. Therefore, the ability of plants to acquire a minimum level of cold hardiness is of great importance and warrants further investigation. This study aimed to evaluate the onset and release of dormancy in apple trees, as well as the dynamics of cold hardiness, comparing environments with different chilling accumulations (Lovo and Horizonte orchards), cultivars ('Fuji', 'Gala', and 'Eva'), and tissues (apical buds, bark, and wood) from 2018 to 2022. This study hypothesizes that apple trees grown in mild winter regions do not experience deep endodormancy, leading to lower cold hardiness. A biological test using single-bud cuttings was conducted to evaluate dormancy dynamics. At the same time, cold hardiness was assessed using electrolyte leakage analysis in 1-year-old shoots samples and visual damage assessment in spurs through laboratory freezing assays. Results indicate that the 'Eva' cultivar does not exhibit deep endodormancy, resulting in lower cold hardiness compared to 'Gala' and 'Fuji'. Cultivars in both environments exhibited cold acclimation; however, the loss of cold hardiness was heterogeneous and rapid. Cold hardiness varied by tissue type; wood was the most resistant, followed by bark and buds. Plants cultivated in locations with greater and more consistent chilling accumulation exhibited deeper endodormancy and higher cold hardiness. After acclimation, all cultivars, regardless of cultivation site, showed alterations in cold hardiness in response to winter heatwaves.