Quantificação da tolerância ao congelamento de cultivares de macieira cultivadas em Palmas, Paraná

Abstract

One of the main stages of the productive cycle of a temperate fruit tree, such as Apple (Malus domestica), is dormancy. The knowledge about the freezing tolerance of specialized organs, as well as the relationship between the factors that influence the proper budding and flowering of plants, is directly related to their passage through the stages of dormancy. This study aimed to evaluate the freezing tolerance of different apple tree cultivars (’Gala’, ’Fuji’ and ’Eva’), grown in two locations at different altitudes, the Horizonte commercial orchard and the Lovo commercial orchard, both located in the municipality of Palmas - PR. The Mean Time to Bud Break (MTB) test was performed, to understand the dynamics of entry and exit of dormancy and the TL50 (Lethal Temperature of 50%), to quantify the dynamics of acquisition and loss of tolerance to freezing. In order to perform the BMT, 20 brindilla type branches of each cultivar will be collected fortnightly, for the exposure of cuttings with a vegetative bud in a growth chamber. The sprouting of the cuttings will be monitored daily and the average time of the cuttings to sprout from the moment of collection will be evaluated. TL50 evaluation is done by simulating temperatures between 5 and -35 °C for brindila type branch tissues and 5 to -23 °C for mixed spur buds. Evaluation of the TL50 of brindles will be done by quantification of cell leakage by means of electrical conductivity and evaluation of the TL50 of mixed spur buds will be done by means of a scale of grades of the level of visual damage of the internal tissue. The TL50 curves are modeled using nonlinear models to find the temperature that generates 50% tissue damage. Apple plants acquire cold tolerance over the winter, and show a de-climation in early spring. Thermal fluctuations during the winter altered cold tolerance, leaving plants more susceptible to cold after intense heat waves during the winter. The cultivar Eva shows tolerance to cold, but in a more superficial way than the other cultivars, and presents a high risk of freezing loss in the study region.