Screening of Microbial Antagonists and Plant Extracts Against Selected Tomato Pathogens and Their Potential in the Management of Bacterial Wilt

Abstract

Tomato production is greatly affected by major bacterial and fungal phytopathogens such as Ralstonia solanacearum, Fusarium oxysporum f. sp. lycopersici and Alternaria solani. Bacterial wilt, caused by Ralstonia solanacearum, can result in up to 100% yield losses. The disease has no easily affordable and accessible effective management method and therefore farmers are forced to abandon production once the pathogen is established in the greenhouse or field. The main objective of the study was to evaluate the efficacy of local microbial isolates and plant extracts in managing bacterial wilt under field conditions. Microbial antagonists were isolated from soils collected in five counties. Plant extracts of 19 different plants were prepared in ethanol. Screening for activity of the antagonists was conducted using dual culture techniques while the activity of plant extract was assessed using the paper disk diffusion and food poisoned techniques. Degree of activity was measured as the diameter of zone of inhibition for bacteria and diameter of colonies for fungi. The most active antagonists and plant extracts against R. solanacearum in vitro were evaluated for their efficacy under field conditions. The microbial antagonists evaluated included Trichoderma hamatum, T. atroviride, T. harzianum, Bacillus subtilis, Acinetobacter spp., Serratia spp. The plant extracts were from Curcuma longa, Rosmarinum officinallis and Tagetes minuta. Commercial formulations of T. viride (Bio Cure F®) and Pseudomonas fluoresce (Bio Cure B®) were included as standard checks. The products were applied as drenches every two weeks commencing at transplanting until the tenth week after transplanting...................