Interactions of Bacillus amyloliquefaciens FZB42 with the fungal pathogen Rhizoctonia solani in the rhizosphere of lettuce (Lact

Soumitra Paul Chodhury (Graz): Rhizoctonia solani is the causal agent of bottom rot in lettuce (Lactuca sativa). The plant-associated Bacillus amyloliquefaciens FZB42 available as a commercial inoculant has genetic ability to synthesize secondary metabolites like cyclic lipopeptides and polyketides. We evaluated the rhizosphere competence of FZB42 on lettuce growth and health together with its impact on the indigenous rhizosphere bacterial community in field and pot experiments. The disease severity of bottom rot on lettuce was significantly reduced through treatment of young plants with FZB42. We could show that the treatment did not have a major impact on the indigenous rhizosphere bacterial community. However, the bacterial community showed a clear temporal shift depending on plant age. Expression analysis revealed that there was a clear induction of systemic resistance by FZB42 in lettuce plants. In conclusion, we revealed that FZB42 could establish itself successfully in the rhizosphere of lettuce without showing any durable effect on the rhizosphere bacterial community. We also showed that lipopeptides are actually produced by FZB42 in the lettuce rhizosphere and they play an important role in eliciting induced systemic resistance against the attack of R. solani.