Phytotoxic effects of model biofumigation on the host plant and collateral effects to non-target microbiota. ITC effects on rhizosphere bacterial communities

Biofumigation is a biocontrol technique that involves the mulching of Brassica plant tissues into soil to release isothiocyanates (ITCs). Whilst the biocidal effects of ITCs against plant pathogens are well documented, effects on the surrounding microbiome, the host crop and potential ITC pathogen tolerance evolution remain understudied. Here we used an in vivo tomato model system to evaluate the efficacy of ITC against Ralstonia solanacearum plant bacterial pathogen, the surrounding microbiome and the host crop. We found that ITC was efficient at suppressing R. solanacearum growth. However, there was no reduction in host crop disease symptom severity, and we observed ITC tolerance evolution in R. solanacearum. Additionally, weekly ITC exposure reduced soil microbiome richness and eliminated certain rare taxa, but increased network connectivity and reduced the number of negative associations between taxa. Our results suggest that while ITC can successfully inhibit R. solanacearum growth in the soil, disease symptom severity was not alleviated and there were collateral effects on non-target microbiota and pathogen ITC tolerance evolution which could limit the long-term efficiency of biofumigation biocontrol. Further research is hence required to understand the broad-spectrum antimicrobial activity of ITCs in soil microbiomes, phytotoxic effects on host crops and the effects on future pathogen invasion susceptibility.