Climatic factors are of a big importance for the determination of phenological stages of several fruit tree species, including apple, during the pre- and post-blooming periods causing their modifications and consequently affecting the fruit quality and productivity. This study aimed to identify the important dormancy phases (chilling and forcing periods) involved in determination of the flowering time in Gala apple trees in order to estimate temperature and chill/heat requirements, useful to assess the effect of climatic factors and phenological modifications on apple productivity and quality. Phenological and climatic data (temperatures, rainfall, irrigation, chilling and heat requirements) were collected, calculated, and measured from orchard in Imouzzer-Kandar, Morocco. Fruit productivity and quality parameters (total yield, fruit weight, size, firmness, and sweetness) were measured. Results showed a prolonged chilling period basing on the pre-blooming phases identified using partial least squares regression. Inadequate chill during warm seasons (insufficient chilling requirements) induces some phenological perturbations: late flowering, extended flowering duration, and period from flowering to harvesting. These phenological anomalies affect negatively the fruit quality of apple as a cause of inadequate climatic factors, mainly temperature and chilling requirements during the chilling period. Our findings demonstrated that sufficient chilling and heat requirements correlate positively with fruit weight, size, and firmness, although the low irrigation applied during the period from flowering to the harvesting times. In unfavorable conditions, total yield and fruit sweetness could be improved by supplementary irrigation during the same period. Practically, chilling requirements of 645-677 chill hours, 709-1157 chill units, and 43.4-55.2 chill portions according to 0-7 °C, Utah model, and Dynamic model respectively and heat requirements of 26,290-27,057 growing degree hours are sufficient for good fruit quality. These are equivalent to temperature of 9.3-9.9 °C during the chilling period and 11.1-12.5 °C during the forcing period. These findings are useful for eventual management measures in order to improve apple production in their cropping area. At long terms, we propose necessity of rearrangement of high-chill apple varieties by low-chill cultivars as a way of apple crop adaptation to climate variations.
Keywords: Apple; Chilling and heat requirements; Climate variation; Fruit quality; Phenology; Yield.