Evaluation of Antibacterial Potentials of Aqueous Extracts of Two Capsicum Fruits in the Management of Xanthomonas axonopodis pv. phaseoli

Abstract

Common bacterial blight of cowpea is caused by Xanthomonas axonopodis pv. phaseoli (Xap) which can devastate both the seedlings and adult plants, thereby yield reduction. The experiment was carried out by evaluating the antibacterial potential of two aqueous pepper fruit extracts; Capsicum chinense cv. Bonnet and Capsicum annuum cv. Red bell. The extracts were prepared at 25, 50 and 75% w/v concentrations. Sterile distilled water (SDW) was used a negative control while streptomycin sulfate (0.2% w/v) served as positive control. Bactericidal evaluation of the extracts was carried out using agar well diffusion method, laid out in a Completely Randomized Design (CRD) with three replications. Pathogenicity, morphological and biochemical tests of the isolates confirmed the characteristics of the bacterium. The results revealed that the two extracts had inhibitory effects on the two isolates of the bacterium tested. At 75% concentration for both extracts and 72 hrs after incubation, Bonnet pepper extract recorded inhibition zones of 23.50 mm and 15.27 mm while Red bell pepper extract had 23.23 mm and 12.60 mm on Xap1 and Xap2 isolates, respectively. These values were significantly higher than inhibition zones (11.20 mm and 8.17 mm) recorded for Bonnet pepper extract and inhibition zones (11.20 mm and 9.53 mm) recorded for Red bell pepper extract at 50% concentration. It could be concluded that, the two Capsicum fruit extracts have promising potential in the management of Xanthomonas axonopodis pv. phaseoli (Xap) at 75% concentration which could serve as alternative to synthetic chemicals for poor resource farmers.