A compound of salicylates, copper and zinc increases coffee resistance against infection by <i>Hemileia vastatrix</i>

Abstract Coffee leaf rust (CLR), caused by the biotrophic fungus Hemileia vastatrix , has greatly impacted coffee production worldwide due to reductions in yield. This study investigated the potential use of Re‐leaf® (salicylates [0.69%], copper [0.5%] and zinc [6%]) to reduce CLR severity by boosting host defence reactions. A 2 × 2 factorial experiment was arranged with plants sprayed with water (control) or Re‐leaf (induced resistance [IR] stimulus) and noninoculated or inoculated with H . vastatrix . In vitro assays showed germ tubes were not formed on urediniospores exposed to IR stimulus at 5–12.5 mL/L and urediniospore germination was significantly lower as rates increased. CLR severity was also significantly reduced compared to the control, with the area under CLR progress curve and intensity of fungal sporulation significantly lower by 96% and 92%, respectively, and incubation period higher by 54% compared to control. The IR stimulus‐sprayed and infected plants showed better photosynthetic performance, preservation of photosynthetic pigments, greater activity of defence‐related enzymes and a more robust antioxidative metabolism compared to water‐sprayed and infected ones. The higher concentration of superoxide anion radical for IR stimulus‐sprayed and infected leaves may intensify cell defence reactions besides having a fungistatic effect. These results strongly support the potential use of IR stimulus to boost defences in coffee tissues and hamper the infection process of H . vastatrix . Its fungistatic effect against germination of fungal urediniospores should also be considered as a strategy to reduce the amount of inoculum required to start a CLR epidemic under field conditions.