Root colonisation and induction of plant defence-associated signalling pathways in Arabidopsis thaliana by Serratia marcescens, Streptomyces galilaeus, and Trichoderma viride

Abstract Some microorganisms that are antagonistic to phytopathogens can activate induced systemic resistance (ISR) in plants. We sought to determine whether Streptomyces galilaeus CFFSUR-B12, Serratia marcescens CFFSUR-B2, and Trichoderma viride CFFSUR-A21 – strains recognised for their antagonistic capacity – could colonise the roots of and induce resistance in Arabidopsis thaliana. The antagonistic activity of Colletotrichum spp. was determined in dual-culture assays. Strains were inoculated separately in the roots of A. thaliana to study root colonisation and activation of ISR in leaves. PR1 and PDF1.2 expression was monitored by RT-qPCR in leaves. Serratia marcescens CFFSUR-B2 colonised the rhizoplane and endorhizosphere, whereas Str. galilaeus CFFSUR-B12 and T. viride CFFSUR-A21 only colonised the rhizoplane. Serratia marcescens and T. viride induced co-expression of PR1 and PDF1.2, while Str. galilaeus induced only PDF1.2 expression. These findings reveal new avenues for research into plant disease management in the humid tropics.