Biocontrol Potential of Selected Lamiaceae Species Against Ralstonia solanacearum (Smith) Causing Wilting in Hot Pepper in Ethiopia.

Abstract

Background: Hot pepper (Capsicum annuum L.) is a significant crop worldwide, including in Ethiopia, but its yield is radically dropping owing to several biotic factors such as bacterial wilting, necessitating the development of environmentally benign plant-based natural treatments to address these challenges. Therefore, this study seeks to evaluate the biocontrol potential of selected Lamiaceae species against Ralstonia solanacearum in hot pepper cultivation.

Methods: Ethanolic leaf extracts from six plant species were prepared using the maceration technique and characterized through qualitative and quantitative phytochemical analyses. R. solanacearum was isolated from infected hot peppers and identified using biochemical tests. The antibacterial activity of plant crude extracts was assessed in vitro against R. solanacearum using the agar well diffusion assay. The broth microdilution method was used to determine the minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC). The data were analyzed using analysis of variance (ANOVA).

Results: All of the examined plants' ethanol extracts contain alkaloids, phenolics, and terpenoids. Mentha spicata had the highest total phenolic content (184.5 ± 0.5 mg GAE/g dry sample), whereas Salvia schimperi had the highest total flavonoid content (144.3 ± 0.3 mg CE/g). Plant extracts revealed a dose-dependent gradual increase in the inhibitory zone. M. spicata extract had the highest antibacterial activity (18.33 ± 0.57), followed by S. schimperi (16 ± 1) at 50 mg/mL. The zone of inhibition differed significantly among the analyzed plant extracts (p < 0.05). M. spicata had a lower MIC (6.25 mg/mL) and MBC (12.5 mg/mL).

Conclusion: The Lamiaceae family holds significant potential as a biocontrol agent against R. solanacearum, as antibacterial compounds were found in the extract. Future research should focus on validating M. spicata and S. schimperi extracts through in vivo field trials to develop sustainable, plant-based biopesticides for Ethiopian pepper farmers.