Exogenous soluble sugars modulate disease severity and physiological and biochemical responses in olive (Olea europaea L.) trees infected with Verticillium dahliae Kleb.

Verticillium wilt, caused by Verticillium dahliae Kleb., is a soil-borne disease limiting olive ( Olea europaea L.) production, and its management remains challenging. This study evaluated the effects of soluble sugars, applied alone or in combination with fungicide and Trichoderma biofertilizer, on disease severity and physiological and biochemical responses of naturally infected trees of the ‘Zard’ olive cultivar. Sucrose, glucose, and fructose at different concentrations, fungicide at half and recommended concentrations, and Trichoderma biofertilizer were applied through foliar spray and soil drenching. Disease severity, total phenol, total flavonoid, antioxidant capacity, chlorophyll a , chlorophyll b , total chlorophyll, and carotenoids were assessed at different stages, and treatment, time, and treatment × time effects were analyzed using ANOVA followed by Tukey’s test. Responses varied with sugar type, concentration, application method, and assessment time. Sucrose at 100 ppm produced the most consistent favorable responses, particularly under soil drenching, where it increased total phenol and antioxidant responses and reduced disease severity. Under foliar spray, several sugar-based treatments improved physiological and biochemical traits, while 100 ppm sucrose and selected sugar–fungicide combinations improved chlorophyll and carotenoid contents. Trichoderma biofertilizer also showed beneficial effects on disease severity and selected physiological and biochemical traits. Several sugar combinations with half-rate fungicide produced responses comparable to treatments receiving the recommended fungicide concentration, suggesting their potential to contribute to reduced fungicide inputs. Overall, soluble sugars, particularly low-concentration sucrose, can modify disease severity and physiological and biochemical responses of olive trees infected with V. dahliae . Their use alone or in combination with Trichoderma and reduced-rate fungicides may complement integrated disease management and potentially contribute to reducing fungicide inputs.