Efficacy of aqueous extracts from ten local plant species on three bacterial pathogens of cassava under laboratory and field conditions in south West Nigeria

This study investigates the antibacterial efficacy of aqueous extracts from ten local plant species against three major bacterial pathogens of cassava: Xanthomonas axonopodis, Erwinia carotovora subsp. carotovorum, and Agrobacterium tumefaciens. Laboratory assays using agar well diffusion revealed that extracts of Azadirachta indica and Tithonia diversifolia exhibited the largest zones of inhibition against Xanthomonas axonopodis (24 mm and 22 mm, respectively, at 200 mg/mL), while Commelina diffusa and Euphorbia heterophylla showed the least activity. Minimum inhibitory concentration (MIC) tests confirmed the strong antibacterial potential of Azadirachta indica and Tithonia diversifolia, both displaying the lowest MIC values (50 mg/mL) against Xanthomonas axonopodis. Field trials demonstrated that cassava plots treated with Azadirachta indica and Tithonia diversifolia extracts had the lowest disease incidence (15% and 18%, respectively) compared to the control (55%) and chemically treated plots (25%). Disease severity ratings were also significantly reduced in these plots, with mean scores of 1.5 and 1.7, respectively, versus 4.0 in the control and 2.3 in chemically treated plots. These findings highlight the potential of Azadirachta indica and Tithonia diversifolia extracts as effective, natural alternatives for managing bacterial diseases in cassava, supporting the advancement of sustainable agricultural practices in Nigeria.