The effect of sooty mold on fluorescence and gas exchange properties of olive tree

Sooty mold is a complex of dark-pigmented fungi that covers leaves and branches of the olive tree (Olea europaea L.). This coverage can bring several consequences for the plant, such as decrease of the photosynthetic rate. Therefore, this study aims to understand the effect of sooty mold on fluorescence and gas exchange of olive leaves. Olive leaves were field-collected and histological, physiological (water content, fluorescence parameters, and carbon dioxide fluxes), and biochemical (osmolality; chlorophyll a, b, and a/b contents; and lipid peroxidation) analyses were performed in healthy leaves and in leaves covered with sooty mold. Histological analysis revealed a complex fungal hyphae proliferation on both leaf surfaces of covered leaves that predominated on the abaxial surface. Sooty mold-covered leaves showed significantly lower levels of water content and of basal (F0), maximal (Fm), and variable fluorescence (Fv). The proliferation of the sooty mold resulted in a decrease of fluorescence parameters, foliar free gas exchanges, and water content. Based on these results, we can conclude that sooty mold infection could affect light reaching leaves and the normal physiological metabolism of the plant (as photosynthesis) would be affected, with consequences for production.