Enzymatic Activity in Essential Oil-Treated and Pathogen-Inoculated Corn Plants

Bipolaris maydis and Exserohilum turcicum are important fungal pathogens that cause leaf blight in corn whose control have been difficult. Essential oils are a promising and environmentally friendly alternative for disease management, but the mechanisms of action remain poorly studied. Here, we aimed to assess the effect of B. maydis and E. turcicum as well as the essential oil of Morinda citrifolia in the activity of plant defense enzymes in corn plants. Experiments were carried out in a completely randomized design with three replications and six treatments as they follow: (T1): corn plants inoculated with B. maydis; (T2): corn plants inoculated with E. turcicum; (T3): corn plants treated with essential oil of M. citrifolia (0.25%) and inoculated with B. maydis; (T4): corn plants treated with essential oil of M. citrifolia (0.25%) and inoculated with E. turcicum; (T5): corn plants treated with essential oil of M. citrifolia (0.25%); and (T6): corn plants non-inoculated and treated with distilled water. Protein content (PC) and activities of the enzymes ascorbate peroxidase, catalase, chitinase (CHI), peroxidase (POX) and superoxide dismutase (SOD) were assessed. PC was significantly decreased, whereas CHI and SOD activity was higher in T1-T5 compared to T6. T4 and T5 significantly increased POX activity relative to T6. Therefore, our findings suggest that the essential oil of M. citrifolia may play an active role in disease control by activating defense enzymes in corn plants.