Combining in vitro and in vivo screening to identify efficient
Pseudomonas biocontrol strains against the phytopathogenic bacterium
Ralstonia solanacearum
Abstract
While plant pathogens are traditionally controlled using synthetic
agrochemicals the availability of commercial bactericides is still
limited. One potential control strategy could be the use of
plant-growth-promoting bacteria (PGPBs) to suppress pathogens via
resource competition or the production of antimicrobial compounds. This
study aimed to conduct in vitro and in vivo screening of eight
Pseudomonas strains against Ralstonia solanacearum (the causative agent
of bacterial wilt) and to investigate underlying mechanisms of potential
pathogen suppression. We found that inhibitory effects were Pseudomonas
strain-specific, with strain CHA0 showing the highest pathogen
suppression. Genomic screening identified 2, 4-diacetylphloroglucinol
(DAPG), pyoluteorin, and orfamides A and B secondary metabolite clusters
in the genomes of the most inhibitory strains, which were investigated
further. While all these compounds suppressed R. solanacearum growth,
only Orfamide A was produced in the growth media based on mass
spectrometry. Moreover, orfamide variants extracted from Pseudomonas
cultures showed high pathogen suppression. Using the Micro Tom tomato
cultivar, it was found that CHA0 could reduce bacterial wilt disease
incidence with one of the two tested pathogen strains. Together, these
findings suggest that a better understanding of Pseudomonas-Ralstonia
interactions in the rhizosphere is required to successfully translate in
vitro findings into agricultural applications.