Dormancy Studies in Apple Trees Cultivars Grown under Mild Climate

Aims: In order to research dormancy dynamics in apple (Malus domestica Borkh.) cultivars ‘Eva’ (low chilling requirement) and ‘Mollie’s Delicious’ (high chilling requirement) in the year of El Niño occurrence.

Study Design: Complete randomized experimental design was arranged in bifactor scheme with four replications to each cultivar. Factor A was the conditions (Field condition and Forcing condition), and factor B comprised the sampling date (1, 2, 3, 4, 5), differing on chilling accumulation hours, which were measured by Embrapa climatic stations, cv. ‘Mollie’s Delicious’ (89 h, 156 h, 176 h, 324 h, 367 h), and cv. ‘Eva’ (60h, 119h, 124h, 161h, 211h), resulting on a bifactorial 2x5 for each cultivar.

Place and Duration of Study: Experiment was developed from adult apple orchards trees at Arroio do Padre (31°43’S and 52°41’W) and Capão do Leão (31°56’S and 52°29’W) located near Pelotas, Southern of Brazil, between June 2014 to September 2014.

Methodology: Biological tests were performed, named Tabuenca’s test (forcing conditions) and Single Bud Test (average time for budburst).

Results: During Tabuenca’s evaluation period, cv. ‘Mollie’s Delicious’ presented steady humidity until late winter, where humidity inside the bud showed a high increase, suggesting the end of endodormancy. Cultivar ‘Eva’, in the same test, showed steady humidity in the whole period, not indicating the end of endodormancy. In the Single Bud Test, cv. ‘Eva”, when subjected to forcing conditions, presented a proportional budding humidity curve with an atypical behavior and a high sprouting rate, suggesting that it has not entered into endodormancy stage.

Conclusion: The study suggests that Tabuenca’s test and average time for budburst methods were not efficient to measure the end of endodormancy in cv. ‘Eva’ under warm winter conditions during the El Niño years. Evidence is presented that chill insufficiency is already happening in several global locations and it may causes unexpected response in crops.