Biological control of the tomato wilt caused by Clavibacter michiganensis subsp. michiganensis using formulated plant growth-promoting bacteria

Rhizobacteria have been reported as bioagents of bacterial diseases and plant growth promoters. The present in vitro study and greenhouse experiment aimed to evaluate the efficiency of Bacillus subtilis, B. amyloliquefaciens, Pseudomonas fluorescens, and P. aeruginosa for the control of bacterial wilt caused by Clavibacter michiganensis subsp. michiganensis and promoting the growth of tomato plants. Effect of formulated and cell suspensions on disease reduction and the pathogen colonization frequency in plants were assessed. The tested bacterial species were able to inhibit the growth of the causal pathogen in vitro. Under greenhouse conditions, the highest reduction in disease severity was detected in tomato plants treated with formulated B. amyloliquefaciens (74.4%), followed by P. aeruginosa (66.7%), while the lowest reduction occurred in tomato seedlings treated with cell suspensions of P. fluorescens (40%) and B. subtilis (53.3%). The four bacterial species produced siderophores, hydrogen cyanide and indole acetic acid in different concentrations. The study confirmed that the use of the four bacterial species as suspensions or formulations could be applied as future eco-friendly alternatives to the synthetic fungicides for controlling the bacterial wilt of tomato caused by C. michiganensis subsp. michiganensis.