Induction of defense-related proteins in tomato roots treated with Pseudomonas fluorescens Pf1 and Fusarium oxysporum f. sp lycopersici

Pseudomonas fluorescens isolate Pfl was found to protect tomato plants from wilt disease caused by Fusarium oxysporum f. sp. lycopersici, Induction of defense proteins and chemicals by P fluorescens isolate Pfl against challenge inoculation with F oxyxporum f. sp. lycopersici in tomato was studied. Phenolics were found to accumulate in bacterized tomato root tissues challenged with F oxysporum f. sp. lycopersici at one day after pathogen challenge. The accumulation of phenolics reached maximum at the 5(th) day after pathogen challenge. In pathogen-inoculated plants, the accumulation started at the 2(nd) day and drastically decreased 4 days after the pathogen inoculation. Activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) increased in bacterized tomato root tissues challenged with the pathogen at one day after pathogen challenge and activities of PAL and PO reached maximum at the 4(th) day while activity of PPO reached maximum at the 5(th) day after challenge inoculation. Isoform analysis revealed that a unique PPO I isoform was induced and PO I and PPO2 isoforms were expressed at higher levels in bacterized tomato root tissues challenge inoculated with the pathogen. Similarly, beta-1,3 glucanase. chitinase and thaumatin-like proteins (TLP) were induced to accumulate at higher levels at 3-5 days of challenge inoculation in bacterized plants. Western blot analysis showed that chitinase isoform Chi2 with a molecular weight of 46 kDa was newly induced due to R fluorescens isolate Pfl treatment challenged with the pathogen. TLP isoform with molecular weight of 33 kDa was induced not only in P. fluorescens isolate Pfl-treated root tissues challenged with the pathogen but also in roots treated with P fluorescens isolate Pfl alone and roots inoculated with the pathogen. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restriction of invasion of F oxysporum f. sp. lycopersici in tomato roots.