Evaluation of the Inhibitory Effect of Extracts of two Medicinal Plants on the Development of Phytophthora megakarya in Theobroma cacao

Abstract

The production of cocoa (Theobroma cacao) is threatened by the attack of pathogens, the most aggressive of which is Phytophthora megakarya. The study of the inhibitory effects of Ocimum basilicum and Psidium guajava leaf extracts on growth in vitro and in vivo conditions would be necessary to deal with this pathogen. Thus, the aqueous and ethanolic extracts of the two plants at different concentrations and slices of mycelium 5 mm in diameter were used. The in vivo sensitivity of the pathogen to the extracts was carried out by innoculating an inoculum/extract complex with a volume of 20 μL in the cavities of the pods. The means obtained were separated by Duncan’s multiple tests at the 5% probability threshold. The results obtained show that the ethanolic extracts of plants under in vitro conditions completely inhibit the mycelial growth of the pathogen at a concentration of 4mg/mL and more. In contrast, the aqueous extracts of basilicum and guajava reduce their growth by 49, 53% and 32.5%, respectively, at a concentration of 8 mg/mL. The pods inoculated with the aqueous extract of basilicum at a concentration of 4mg/mL show no sign of necrosis, as well as those with ethanolic extracts of guajava and basilicum at a concentration of 6 mg/mL after six days of inoculation. These extracts have been shown to be effective and can, therefore, be used as an alternative in the control of brown rot of cocoa pods.