S11 - Session P2 - Effect of temperature on the dormancy process and satisfying of chilling requirements for apple in Morocco

Authors: Adnane El Yaacoubi *, Meryem Erami, Ossama Kodad

Temperature plays a primordial role in determining the phenological phases preceding the apple flowering period (dormancy, breaking dormancy, flowering…), particularly during the cold period (winter). This later, constitute an important period to satisfy chilling requirements necessary for breaking dormancy in floral buds. In fact, when chilling requirements are not sufficiently satisfied during winter, for apple, variations in the development cycle are caused, starting with disturbances in the dates of breaking dormancy, which modify the phenology of budburst, flowering, and consequently affect vegetative development, maturity and fruit production. This study aims to characterize the bud dormancy in order to estimate the chilling and heat requirements of apple. To reach this goal, we studied four apple varieties (Golden Delicious, Gala, Top Red and Starking) conducted under Moroccan climate conditions. The determination of breaking dormancy dates of each variety was approached experimentally using Tabuenca's test. To estimate chilling and heat requirements, two models were used respectively: Dynamic and Growth Degree Hours models. Monitoring phenological stages was conducted in field to link period of flowering to chilling and heat requirements of each variety. Results showed that the dates of breaking dormancy were earlier for Gala, intermediate for Starking and Top Red; late for Golden Delicious. This later showed, in consequence, high chilling requirements with longer chilling period, explained by lack of chilling during winter. Gala was the lowest chill variety. Our observation in field, highlighted some symptoms of lack of chilling such, heterogeneity of flowering, extended flowering period, which could have impact on fructification and consequently on production. Thus, in the context of global warming, measures of adaptation to lack of chill has become necessary and urgent, by creating new low-chill-varieties or apple tree plantations in high altitudes.