IN VITRO EFFICACY OF FIVE ESSENTIAL OILS ON THE MYCELIAL GROWTH OF ASPERGILLUS NIGER ISOLATES FROM ONION BULBS

Onion is a vegetable produced in practically all regions of Burkina Faso. Many efforts are being made to increase national production, but in storage, the loss due to black rot limits the disponibility of local bulbs during the year. The essential oils of Ocimum gratissimum, Ocimum basilicum, Cymbopogon citratus, Cymbopogon Gigantes, and Lippia multiflora, known to have antifungal properties, were added to a PDA medium and assessed in vitro at 500, 1000, 1500 and 2000 ppm concentrations on mycelial growth of isolates of Aspergillus niger. After the 4- and 7-day incubation, there was a highly significant difference between the essential oils at concentrations of 500 and 1000 ppm (p<0.001), and Ocimum gratissimum is considered the best essential oil with an inhibition percentage varying between 47.3 and 89.5%. However, all essential oils showed 100% total inhibition at 1500 ppm and the essential oils of Ocimum gratissimum and Cymbopogon giganteus demonstrated fungicidal effects at concentrations of 1500 and 2000 ppm, respectively. The intense antifungal activity of Ocimum gratissimum oil is related to the presence of thymol, a potent antioxidant responsible for the fungal activity. The activity of Ocimum gratissimum oil must also be tested in vivo to develop biopesticide formulations for the control of onion spoilage fungi.