Université de Moncton, Department of Biology, Moncton, NB, Canada, E1A 3E9.
Bacterial canker caused by Clavibacter michiganensis subsp. michiganensis is known to cause significant economic losses to tomato production worldwide. Biological control has been proposed as an alternative to current chemical containment methods, which are often inefficient and may leave adverse effects on the environment. However, only little headway has so far been made in developing biocontrol strategies against C. michiganensis subsp. michiganensis. To address this knowledge gap, we investigated the antagonistic capacity of PCA, produced by Pseudomonas sp. LBUM223, and DAPG and HCN, both produced by Pseudomonas sp. LBUM300, on C. michiganensis subsp. michiganensis under in vitro and in planta conditions. Nonsynthesizing isogenic mutants of the producer strains were also developed to further dissect the role of each individual metabolite on C. michiganensis subsp. michiganensis biological control. Novel specific quantitative polymerase chain reaction TaqMan assays allowed quantification of C. michiganensis subsp. michiganensis in tomato plants and rhizospheric soil. Pseudomonas spp. LBUM223 and LBUM300 significantly repressed C. michiganensis subsp. michiganensis growth in vitro, while their respective nonproducing mutants showed less or no significant antagonistic activity. In planta, only Pseudomonas sp. LBUM300 was capable of significantly reducing disease development and C. michiganensis subsp. michiganensis rhizospheric population, suggesting that the production of both DAPG and HCN was involved. In summary, simultaneous DAPG/HCN production by Pseudomonas sp. LBUM300 shows great potential for controlling bacterial canker of tomato.