A Zinc Polyphenolic Compound Increases Maize Resistance Against Infection by Bipolaris maydis

Maize leaf blight (MLB), caused by the fungus Bipolaris maydis, is an important disease affecting maize production. In order to minimize the use of fungicides in agriculture, nutrient-based resistance inducers may become a promising alternative to manage MLB. The goal of this study was to investigate the potential of Semia^® (zinc (20%) complexed with a plant-derived pool of polyphenols (10%)) to hamper the infection of maize leaves by B. maydis by analyzing their photosynthetic performance and carbohydrate and antioxidative metabolism, as well as the expression of defense-related genes. Plants were sprayed with water (control) or Semia^® (referred to as induced resistance (IR) stimulus hereafter) and not inoculated or inoculated with B. maydis. The mycelial growth and conidium germination were significantly reduced by the IR stimulus in vitro. The MLB severity was significantly reduced by 76% for IR-stimulus-sprayed plants compared to plants from the control treatment. For infected and IR-stimulus-sprayed plants, the glucose, fructose, sucrose, and starch concentrations were significantly higher compared to inoculated plants from the control treatment. The activity levels of superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase were significantly higher for the IR-stimulus-sprayed plants compared to plants from the control treatment. Less impairment on the photosynthetic apparatus (higher values for leaf gas exchange (rates of net CO₂ assimilation, stomatal conductance to water vapor, and transpiration) and chlorophyll a fluorescence (variable-to-maximum Chl a fluorescence ratio, photochemical yield, and yield for dissipation by down-regulation) parameters)) along with a preserved pool of chlorophyll a+b and carotenoids were noticed for infected and IR-stimulus-sprayed plants compared to infected plants from the control treatment. The defense-related genes IGL, CHS02, PR1, PAL3, CHI, and GLU were strongly up-regulated in the leaves of IR-stimulus-sprayed and infected plants compared to infected plants from the control treatment. These findings highlight the potential of using this IR stimulus for MLB management.