Lipopolysaccharide of Enterobacter asburiae strain RS83: A bacterial determinant for induction of early defensive enzymes in Lactuca sativa against soft rot disease

Abstract

Lipopolysaccharides (LPS) from plant pathogenic bacteria have been reported to be determinants of induced systemic resistance (ISR) for plant disease suppression. The role of bacterial LPS in ISR elicited by beneficial rhizobacteria has not been extensively reported. The capacity of Enterobacter asburiae strain RS83 to induce ISR against several diseases was previously demonstrated under greenhouse and field trials. The objectives of this study were (1) to examine the capacity of LPS extracted from strain RS83-mediated ISR in Lactuca sativa against bacterial soft rot disease and (2) to evaluate the enhanced early defensive-related enzymes induced by LPS of strain RS83 implicated for disease restraint. LPS from strain RS83 was first recovered in a hot MgCl2-Triton X-100 solution, solubilized with EDTA Triton X-100, and finally precipitated with MgCl2. The LPS was further tested for elicitation of ISR in lettuce against Pectobacterium catovorum subsp. catovorum (Pcc) under in vitro bioassay system. A colorimetric assay for superoxide dismutase (SOD) and peroxidase (PO) activities was performed. The results showed that lettuce treated with LPS of strain RS83 had less (P⩽0.05) disease incidence about 90% than the non-induced pathogen control. Before challenge with the pathogen, significant increase of SOD activity in plants induced with LPS of strain RS83 were 92% greater than the non-induced pathogen control. Only little increase of greater PO activity occurred in treatment induced with LPS of strain RS83 compared to the control. Both SOD and PO activities were significantly accelerated from 24 h to 72h after challenge compared to the control. These results suggest that LPS of strain RS83 plays a role in the induction of early defensive-related enzymes in lettuce against soft rot disease caused by Pcc.