Antifungal activity of lemongrass and thyme essential oils and effect on gray mold control and postharvest quality of ‘Italia’ grape

The aim of this study was to test the hypothesis that lemongrass and thyme essential oils (EOs) reduce Botrytis cinerea development and control gray mold in ‘Italia’ grapes. The fungitoxicity evaluation was performed by EOs direct contact with the pathogen, in culture medium, and by exposure to the EOs volatile phase. Individualized rachis berries were inoculated by subcuticular injection of a conidia suspension and after 4 hours sprayed with the EOs of lemongrass and thyme (100 to 1,000 mg·L-1), or oils blend (500 mg·L-1 thyme + 100 mg·L-1 lemongrass), and then stored at 25 °C / 75% relative humidity. To verify the possibility that the EOs protect the fruit against B. cinerea, the berries were sprayed with 400 mg·L-1 of each EOs or with the blend (200 mg·L-1 thyme + 200 mg·L-1 lemongrass), and after 24 hours inoculated with B. cinerea. On clusters, thyme (800 mg·L-1) and the blend (500 mg·L-1 thyme + 100 mg·L-1 lemongrass) were sprayed 4 hours after inoculation and then stored at 25 and 1 °C. The disease incidence and severity were analyzed, as well as the fruit quality attributes. EOs had antimicrobial effect, in-vitro, incorporated into the culture medium or by volatilization against B. cinerea. On detached berries, the thyme and oil blend reduced the gray mold severity when inoculated 4 hours before spraying. In clusters, thyme at 800 mg·L-1 significantly reduced the gray mold development only in fruits kept at 1 °C, without impairing the clusters quality, which could be an alternative for the disease management in postharvest.