Traditional Malagasy farmers have developed a range of biological methods to restrict plant diseases without reliance on external or synthetic inputs. Five common Malagasy traditional practices demonstrated to be efficient against potato crop bacterial disease in experimental fields have been investigated for their antibacterial (i.e. bacteriostatic and bactericidal effects) and anti-virulence (i.e. anti-quorum sensing and anti-biofilm) activities against two phytopathogens, Pseudomonas aeruginosa and Ralstonia solanacearum. Results show that polar (methanolic) extracts of recipes exert anti-virulence activities rather than bacteriostatic and/or bactericidal activities. Indeed, three recipes (R5, R7 and R9) reduce the expression of QS-dependent virulence factors whereas only recipe (R5) exhibit anti-biofilm activities without affecting bacterial growth. R4 and R6 were not active, suggesting other bacterial targets and/or other bioactivity properties. Innovative approaches, inspired from ancestral practices, should be considered in the struggle against infectious diseases to limit the overuse of antibiotics for controlling infectious plant diseases and to reduce the overspread of multidrug resistant bacteria.
Biofilm, Quorum sensing, Pseudomonas, Ralstonia