Journal of Applied Biosciences (J. Appl. Biosci.) [ISSN 1997 - 5902]
Volume 1: 18 - 31. Published January 2008.
Protection of tomato plants against fusaric acid by resistance induction
Maina M*^., R. Hauschild**, R. Sikora**
*Current address: FACT Biosciences Unit, Westlands, Nairobi, Kenya
**Institute for Plant Diseases, University of Bonn, Nussallee 9, 53115 Bonn, Germany.
^Corresponding author email: m.mwangi@elewa.org
ABSTRACT
Objectives: The rhizobacteria Bacillus sphaericus B43, Pseudomonas fluorescens T58, and P. putida 53 are able to induce systemic resistance (ISR) against Fusarium oxysporum f.sp. lycopersici in tomato. This study investigated if ISR reduced damage by the toxin Fusaric Acid (FA) that is produced by F. oxysporum.
Methodology and Results: Bacteria were applied to the rhizosphere of tomato plants. Chlorophyll content and ion leakage were determined after placing leaf discs in FA. Active oxygen species (AOS), superoxide and hydrogen peroxide levels were determined in leaves of plants injected with FA. Activities of superoxide dismutase, ascorbate and guaiacol peroxidases involved in AOS metabolism were quantified. In untreated plants, FA led to high ion leakage and chlorophyll degradation caused by H2O2 accumulation. All bacteria treatments reduced chlorophyll degradation. Ion leakage was reduced by treatment with P. fluorescens T58 and B. sphaericus B43, while P. putida 53 was less effective. Treatment of plants with bacteria resulted in increased superoxide contents, but varying over time. Increased SOD and GPX activities in untreated plants were suppressed after bacteria treatment. Plants treated with P. fluorescens T58 showed only a transient increase in superoxide. P. putida 53-treated plants removed AOS, but high initial superoxide levels led to membrane damages. Treatment with B. sphaericus B43 suppressed effects of FA, but AOS metabolism showed only slight alterations.
Conclusions and potential applications of findings: The results show that ISR could also protect plant tissues from damage by pathogen toxins, which is a potential new dimension to the known mechanisms of action of biocontrol agents.
Key words: Active oxygen species, Fusarium, induced systemic resistance, rhizobacteria, tomato, Fusaric Acid.
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