Differential Response of Olive Cultivars to Leaf Spot Disease (Fusicladium oleagineum) under Climate Warming Conditions in Morocco

Olive leaf spot (OLS), also called olive scab and peacock eye, caused by Fusicladium oleagineum, is a major disease that causes significant damage to olive trees. However, we still lack information about how cultivar and environmental factors influence disease development. In this study, evaluation of the incidence and severity on twenty olive cultivars (Olea europaea L.), maintained in an ex situ collection in Morocco, was carried out monthly during the period from March to July 2021. Biochemical parameters were also evaluated for each cultivar including leaf chlorophyll, polyphenols and flavonoid contents. Results revealed that the OLS incidence was highly correlated with severity (r = 0.94) and found to be related to climatic conditions and cultivars. The studied cultivars were classified into four major groups, i.e., susceptible, moderately susceptible, moderately resistant and resistant. Finally, our investigations revealed a partial relationship between resistance to the OLS disease and phenolic and flavonoid leaf contents, supporting the assumption of the potential involvement of such components in cultivar resistance to the disease. Overall, our work highlights the importance of characterizing olive cultivar resistance to OLS in driving the choice of the best varieties for an effective control of the disease in specific warming regions such as Morocco.