Antifungal activities of some citrus essential oils against Pyricularia oryzae

Rice is a staple food worldwide because many families depend on it as an everyday source of food. However, there are some agents posing as threat to the availability of rice worldwide thereby threatening food security. Pyricularia oryzae is a fungal agent notable for causing rice blast disease thereby causing shortage in the production of rice. Essential oils (EOs) from peels (fresh and dried) of three species of citrus fruit (lime, grapefruit and tangerine) were investigated for their antifungal activity against P. oryzae. The EOs were extracted and analysed for their composition using standard analytical techniques. Their antifungal activities were also tested on potato dextrose agar (PDA) medium using disc diffusion method and the results obtained were compared with standard antifungal agents. Dried tangerine EO had the highest fungal mycelial growth inhibition (90%) which was followed by fresh tangerine EO (76.2%). The compounds detected in the essential oils composed majorly hydrocarbons and oxygenated hydrocarbons with limonene, beta myrcene and alpha terpineol detected in fairly high amount in all the investigated essential oils. This study, shows that the peels of these citrus fruits could be of great importance in combating the scourge of P. oryzae, reducing the occurrence of rice blast disease, enhancing rice availability as a staple food and by extension, ensuring food security. These attributes highlight the potential benefits of citrus fruit peels instead of regarding them as mere waste materials.