The rhizobacteria isolates Pseudomonas fluorescens T58, Pseudomonas putida 53 and Bacillus sphaericus B43, selected after greenhouse tests for biological control of Fusarium wilt in tomato, were all able to induce systemic resistance (ISR) against Fusarium oxysporum f.sp. lycopersici. The effects of bacteria on accumulation of phenolic compounds, pathogenesis-related proteins and structural changes in cells showed that each bacteria affected plants differently. Phenol accumulation patterns were not affected by bacteria treatments, but a phenolic compound that was accumulated after Fusarium-infection was not detected in plants treated with P. fluorescens T58 or B. sphaericus B43. Peroxidase activity in the stem was stimulated by all three bacteria. The increase due to B. sphaericus B43 occurred transiently three days after bacteria treatment, while peroxidase activities in plants treated with P. fluorescens T58 or P. putida 53 increased six days after bacteria treatment. Chitinase or ß-1, 3-glucanase are not associated with ISR against F. oxysporum. Cell wall modifications were observed after all bacteria treatments and subsequent Fusarium-infection. P. fluorescens T58 induced deposition of callose on cell walls, while isolates P. putida 53 and B. sphaericus B43 induced extrusion of occluding material into the lumina of xylem vessels and thereby inhibited Fusarium.

Key words

Biocontrol, Fusarium oxysporum, Induced systemic resistance, phenols, PR-proteins

FULL PAPER [PDF AVAILABLE HERE ]