Activité antimicrobienne des extraits de streptomyces spp. Vis-à-vis de xanthomonas phaseoli pathovar manihotis (agent responsable de la bactériose vasculaire du manioc)

Abstract

Cameroon's economy remains heavily dependent on its agricultural sector, where cassava (Manihot esculenta Crantz) remains one of the pillars of the country's food security, primarily linked to the tuberous root. Despite this importance, cassava cultivation is under threat from a bacterial disease caused by Xanthomonas phaseoli pathovar manihotis (Xpm), known as cassava vascular bacterial blight. (CBB). The CBB can lead to the destruction of all cassava plants, resulting in decreased production yields and a loss of income for cassava producers. Hence the interest in combating this bacterium in the present study, which aims to evaluate the antimicrobial activity of the metabolic extracts of Streptomyces spp. against Xpm. Toachieve this, Xpm was isolated from cassava leaves affected by CBB, and then characterized. He was then subjected to the inhibitory activity of forty-three (43) isolates of Streptomyces spp. The metabolites produced by the isolates of Streptomyces that showed the best activities were extracted with methanol and then tested at different concentrations on Xpm. The concentrations of the extracts, equal to or greater than the minimum inhibitory concentrations (MIC) obtained in vitro, were then applied to cassava plants previously infected with Xpm, and the assessment of the health status of these plants was carried out over a period of 14 days. This study shows that seven (07) of the forty-three (43) tested isolates exhibited antagonistic activities against Xpm, with inhibition diameters ranging from 13.50 ± 2.12 mm to 27.50 ± 3.54 mm. The Ker-2 and Bel-12 isolates were selected as the most active Streptomyces isolates, with respective MICs of 2 µg/ml and 32 µg/ml, and a preservation effectiveness of infected cassava plants of 12% and 76% over a period of 14 days. The methanolic extract of the Bel-12 isolate thus appears as a biocontrol agent (BCA) for the CBB.