Biological methods for assessment of budbreak in apple trees for modeling dormancy

A biological method was developed to evaluate the dormancy state of apple buds under controlled conditions. Cuttings (20-25 cm long) of ‘Castel Gala’ and ‘Royal Gala’ were sampled during the winter period, evaluating different cold and heat regimes to induce budbreak. Contrasts were tested in plant material processing (single node x intact cuttings), cold storage method to break dormancy in incubator chambers (planted in pots with floral foam x wrapped in plastic film, vertically or horizontally) and budbreak method in plant growth chambers (base immersed in water x planted in floral foam). Intact cuttings stored vertically in the cold represented better the natural interactions between buds than single node cuttings. Budbreak of lateral buds was strongly influenced by apical dominance. Wrapping cuttings in plastic film optimized internal space usage in the incubators and the number of evaluated buds, compared to planting cuttings in pots. During the warm period in the growth chambers, intact cuttings on floral foam resulted in better bud preservation and survival throughout the evaluation period, compared to cuttings with bases immersed in water. The most suitable conditions to evaluate dormancy evolution in apple buds used plastic-wrapped intact cuttings stored vertically during the cold period, with budbreak evaluation in the warm period after planting the cuttings in floral foam. Standardization of methodology helps to obtain better results in the development of physiological models of dormancy.