Boosting photosynthetic machinery and defense priming with chitosan application on tomato plants infected with Fusarium oxysporum f. sp. lycopersici

Physiological processes of plants infected by vascular pathogens are mainly affected by vascular bundle obstruction, decreasing the absorption of water and nutrients and gas exchange by stomatal closure, and inducing oxidative cascades and PSII alterations. Chitosan, a derivative of chitin present in the cell wall of some organisms including fungi, induces plant defense responses, activating systemic resistance. In this study, the effect of chitosan on the physiological and molecular responses of tomato plants infected with Fusarium oxysporum f. sp. lycopersici (Fol) was studied, evaluating the maximum potential quantum efficiency of PSII photochemistry (Fv/Fm), photochemical efficiency of PSII (Y(II)), photochemical quenching (qP), stomatal conductance (gs), relative water content (RWC), proline content, photosynthetic pigments, dry mass, and differential gene expression (PAL, LOXA, ERF1, and PR1) of defense markers. A reduction of 70% in the incidence and 91% in the severity of the disease was achieved in plants treated with chitosan, mitigating the damage caused by Fol on Fv/Fm, Y(II), and chlorophyll contents by 23%, 36%, and 47%, respectively. Less impact was observed on qP, gs, RWC, and dry mass (16%, 11%, and 26%, respectively). Chitosan-treated and Fol-infected plants over-expressed PR1a gene suggesting a priming-associated response. These results demonstrate the high potential of chitosan to protect tomato plants against Fol by regulating physiological and molecular responses in tomato plants.