Determination of xylem connectivity in Malus × domestica dormant gems through dye application

Abstract

Temperate fruit trees, such as apple (Malus × domestica Borkh.), are characterized by the establishment of bud dormancy. Bud dormancy is overcome after exposure to a certain amount of chilling hours (under 7,2 °C), which varies according to species and cultivars. Another feature of bud dormancy is the lack of free water in buds. In regions where chilling exposure is not enough for dormancy overcoming, the application of chemical substances is necessary in order to break dormancy and for even bud break. One of the difficulties faced by growers is to identify the proper timing for the application of those chemical products. In this work, the water transport in buds during dormancy was assessed, with the intent of evaluating the use of patterns of hydrophilic dye uptake as a marker for dormancy status. As plant material, apical twigs of contrasting chilling requirement cultivars were used. 'Castel Gala' which shows a low chilling requirement for bud break and 'Gala Standard', a high chilling requirement cultivar. These materials were subjected to two experiments: evaluation of water status in buds harvested monthly in the field and under forcing conditions for bud break. Dye capitation, water content, and maximum bud break of apical buds were evaluated. The conductivity of the hydrophilic dye on dormant buds and stems is shown to be reduced during winter. Water content and dye uptake are higher during summer and after bud outgrowth than during dormancy, and both increase after hydrogen cyanamide application. However, there was no difference between ecodormant and endodormant buds in relation to water content and conductivity.