Fungistatic activity of essential oils for the control of bipolaris leaf spot in maize

Research institutions have emphasized alternative disease control agents because they represent a great option with beneficial effects on human and animal health and ecosystem balance. Despite the studies already done on botanical fungicides, their effective use requires knowledge about the applicability of natural products to different production systems. The main objective of this study is to evaluate the efficacy of essential oils of Ocimum pupuraceus L., Cymbopogon nardus (L.) Rendle, Cymbopogon citratus (DC.) Stapf, and Lippia sidoides Cham. on the inhibition of mycelial growth and germination of conidia of B. maydis. The other objectives of this study were to perform gas chromatographic and phytotoxicity analyses, and test the control of bipolaris leaf spot using essential oils of L. sidoides applied as a preventive and curative agent. Among the treatments studied, the essential oil of L. sidoides is effective in inhibiting mycelial growth and conidial germination at the concentrations of 5 and 1%, respectively. The main constituent of the oil is thymol (92.68%). The concentration range 0.75-3% of L. sidoides essential oil is phytotoxic to maize plants. Lower values of the area under the progress curve of bipolaris leaf spot are observed at concentrations 0.1-0.5%, when the essential oil was applied as a preventive agent prior to the colonization of plant tissues by the pathogen. The application of the oil as a curative to plants with the disease also shows efficacy at the concentration 0.1%, reducing the severity by more than 54%. These results demonstrate the potential effects of L. sidoides essential oil on preventive and curative control of bipolaris leaf spot in maize and mycelial growth. Key words: Medicinal plants, alternative control, phytopathogens, Zea mays, Bipolaris maydis, Lippia sidoides.