Meetings of the Royal Botanical Society of The Netherlands

Induction of resistance was demonstrated to be involved in the suppression of fusarium wilt of radish by selected PGPR strains of Pseudomonas fluorescens. in a special bioassay. The pathogen. Fusarium oxysporum f.sp. conglulinans, and the PGPR strains were inoculated spatially separated on the plant root. P. fluorescens WCS374, applied in talcum onto the root tips, induced resistance in six radish cultivars differing in their susceptibility to F. oxysporum f.sp. conglutinans. applied in peat onto the root base. Significant suppression of disease by bacterial treatments was generally observed when disease incidence ranged between approximately 40 and 80% in the control treatment, occasionally at higher and not at lower disease incidence. Both P. fluorescens WCS374 and WCS417, and their extracted cell wall material induced resistance, whereas P. putida WCS358 or its cell wall material did not, in the special bioassay. Spontaneous phage-resistant mutants of strains WCS374 and WCS417, lacking the Oantigenic side chain of the lipopolysaccharide, or cell wall material extracted from these mutants, did not reduce disease incidence in this experimental design.