Lack of effective chilling during the dormant season is one of the major problems when apples are growing under a tropical climate. We evaluated the response of different apple cultivars (Golden Delicious, Gala, Fuji, Granny Smith and Jonagold) grown on M9 rootstock with different dormancy-management practices.
The trials were carried out between 2004 and 2006 in a tropical mountain area (Tigray, Ethiopia), where chilling conditions are poor with the aimof improving and synchronizing the bud break and the blossoming period of these apple cultivars. Two-year-old well-feathered trees were planted in two experimental trial sites in a randomized complete block design. Trees were subjected to the following treatments in two sets of experiments: one defoliation per year only; two defoliations per year, one defoliation followed by 1% hydrogen cyanamide (Dormex) treatment; one defoliation followed by 2% Dormex treatment; one defoliation followed by 4% winter oil; one defoliation followed by 0.5% Dormex and 2% winter oil; and a control with no defoliation or dormancy breaking treatments. The results show positive effects of the dormancy breaking agents on the productivity of the trees after defoliation, with comparable results for the effectiveness of both Dormex and winter oil. There were no statistically significant differences between the Dormex doses. The defoliation treatment alone was not sufficient to break dormancy for the cultivars Golden Delicious, Granny Smith or Gala but showed promising results with dormancy breaking
on Jonagold. Yields increased as a result of better lowering time synchronization within a tree but even with the dormancy treatments the length of the flowering period was still spread over five weeks, where under a more temperate climate it lasted two to three weeks. The average fruit weight of Jonagold and Granny Smith can be considered as a good fruit quality while the fruit of other diploid cultivars like Golden, Gala and Fuji were rather small, which indicates that fruit thinning by hand will be a necessity for these cultivars. Red colouration of the apples on the cultivars Gala and Jonagold was excellent and meets the standards necessary for commercialization of these fruits. The sugar concentration of the fruits and the
fruit firmness at harvest was high. The results of these first trials indicate that it is possible to develop new
apple production in the mountain region of Tigray, Ethiopia.