2017 ASHS Annual Conference

Essential oils have been shown to be effective for controlling many plant pathogens and are considered to be safe for consumers and the environment. Anthracnose, caused by the fungus Colletotrichum gloeosporioides Penz., is one the most devastating diseases of tropical fruit crops, including avocado (Persea americana Mill.) and papaya (Carica papaya L.). Symptoms often appear on fruit after ripening, causing damage to the fruit during storage, transit, and marketing. Experiments were conducted to determine the efficacy of five different plant essential oils for postharvest control of anthracnose in avocado and papaya fruit. Essential oils were extracted from savory (Satureja khuzistanica Jamzad.), thyme (Thymus daenensis Celak.), cinnamon (Cinnamomum zeylanicum Blume.), mint (Mentha piperita Willd.), and lavender (Lavandula angustifolia Mill.) plants, and chemical components of each oil were identified by GC-mass spectroscopy. The polymerase chain reaction (PCR) method using the internal transcribed spacer (ITS) primer confirmed the identity of the C. gloeosporiodes isolate. Antifungal activity was evaluated by artificially inoculating fruit with C. gloeosporioides and then spraying the essential oils on the fruit immediately after inoculation. The essential oils were tested at concentrations of 0, 500, 1000 and 2000 μl L^-1. After storing the fruit for three weeks at 12±1°C followed by one week at room temperature (24±1°C), lesion diameter, disease severity, and fruit firmness were assessed. For both avocado and papaya, savory and thyme oils applied at 2000 μl L^-1 exhibited the strongest antifungal activity, reducing expansion of necrotic lesions around the inoculation sites on the fruit by 58-64% compared to the control. Also, at a concentration of 2000 μl L^-1, savory and thyme oils decreased disease severity more and decreased fruit firmness less than any of the other essential oils. This study showed that foliar application of savory or thyme oil is extremely effective as a natural fungicide for controlling anthracnose decay and prolonging storage life of avocado and papaya fruit.