Potential vulnerability of Moroccan apple orchard to climate change-induced phenological perturbations: effects on yields and fruit quality.

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.

Assessment of sustainable deficit irrigation in a Moroccan apple orchard as a climate change adaptation strategy.

This study was conducted over three consecutive years, 2015, 2016 and 2017, in the Imouzzer Kander region located in northwestern Morocco. The main objective is to evaluate apple tree responses to two sustainable deficit irrigation strategies with 75% (T2) and 50% (T3) of calculated crop evapotranspiration (ETc), compared to a control irrigated with 100% ETc (T1). During the three experiment years, estimated reference evapotranspiration (ET0) was 630, 684 and 728 mm, respectively, in 2015, 2016 and 2017. Under the two restricted regimes, shoot length and fruit size evolution were not significantly affected. During the fruit set of 2017, no significant effects of sustainable deficit irrigation on the relative water content were observed, whereas they increased significantly during the fruit-swelling stage for the T3 treatment. Likewise, net CO2 assimilation (An) was not affected by the irrigation dose, whereas it increased significantly and inversely proportional to the amount of applied water during fruit swelling. Thus, under our experimental conditions, the trees subjected to extreme deficit irrigation (T3) were not stressed at either stage. Moreover, deficit irrigation at 75% ETc increased apple yield significantly. In contrast, deficit irrigation at 50% ETc throughout the cycle was not enough to maintain an acceptable fruit size for the three studied campaigns. However, the best qualitative performance, notably for fruit firmness and sugar content, was attributed to this irrigation regime (T3).