Inhibitory effects of aqueous and ethanolic extracts of pepper (Capsicum annuum) on the development of necrosis caused by Phytophthora megakarya in Theobroma cacao

Abstract

The cocoa tree (Theobroma cacao L.), also called "food of the gods", is a plant mainly cultivated for its beans. However, the cultivation of this plant is confronted with many parasitic attacks among which, attack due to Phytophthora megakarya which causes the most yield loss. The Control of this pathogen consisted in involving the use of aqueous and ethanolic extracts of pepper and two strains of Phytophthora megakarya in order to improve cocoa tolerance against the attack of this pathogen. These aqueous and ethanolic extracts were prepared in the laboratory and incorporated into Potato Dextrose Agar and Small Pea Agar culture media at concentrations (g / ml) of 10^-1, 10^-2, 10^-3 and 10^-4, each containing a strain of Phytophthora megakarya. The results obtained revealed that all pepper treatments significantly inhibited the growth of Phytophthora megakarya with a 100% inhibition rate in the aqueous extract regardless of the strain used and inhibition rates of 89.33%. ; 63.35%; 54.39%; 42.86%; 100%; 70.22% and 57.54% for the ethanolic extract depending on the concentrations applied. In vivo treatment of leaf discs and pods detached prior to infection with Phytophthora megakarya resulted in significant inhibition, thereby reducing the incidence rate of disease severity. The values of this incidence vary from 0.1 to 1.2 for a percentage ranging from 0.5% to 20% of the severity of the disease depending on the nature of the extract of applied pepper. At concentrations (g / ml) 10^-1, 10^-2, 10^-3 and 10^-4, the aqueous extract completely inhibited the growth of mycelium and the development of Phytophthora megakarya spores while the ethanolic extract of pepper showed its inhibitory power at the concentration 10^-1 g/ml. The use of crude aqueous extracts or even diluted of pepper can therefore be considered in the fight against black pod desease in Cameroon.

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Keywords: Phytophthora megakarya, Theobroma cacao, Capsicum annuum, percentage of inhibition, biological control, black pod desease