Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2006
Publication Date: 12/19/2007
Citation: Panina, Y., Fravel, D.R., Shcherbakova, L.A., Baker, C.J. 2007. Biocontrol and plant pathogenic fusarium oxysporum-induced changes in phenolic compounds in tomato leaves and roots. Journal of Phytopathology. 155:475-481. Interpretive Summary: Biological control is being investigated as an environmentally friendly tool for the management of Fusarium wilt of tomato and other crops. Our previous work showed that the soil-inhabiting, non-pathogenic fungus Fusarium oxysporum strain CS-20 triggered responses in tomato to make it less susceptible to a pathogenic form of the same fungus. Chemical compounds are produced in tomato to help defend it from pathogens. We found that specific chemical compounds, particularly ferulic acid, are stimulated in tomato by strain CS-20. Some compounds are stimulated more by CS-20 than by the pathogen, and some less. We also found that very low amounts of strain CS-20 can stimulate these responses, sometimes more than higher amounts of CS-20. This information will be used by scientists developing non-chemical control methods for plant diseases.
Technical Abstract: The biocontrol fungus Fusarium oxysporum strain CS-20 was previously shown to reduce incidence of Fusarium wilt of tomato through an uncharacterized host-mediated response. Since phenolic compounds are involved in the defense response of tomato to pathogens and other stressors, this work was undertaken to determine if biocontrol strains induced changes in phenolic compounds in leaves and roots of tomato seedlings in the presence and absence of pathogenic F. oxysporum f. sp. lycopersici. Roots of intact, bare-root tomato seedlings were placed in water or aqueous fungal spore suspensions. Two biocontrol F. oxysporum strains (CS-20 [host-mediated mechanism] and 8SSK [control mechanism unknown]) and two plant pathogenic strains of F. oxysporum f. sp. lycopersici race 1 were used. After 24 or 72 h exposure, phenolic compounds were extracted from leaves and roots before identification by HPLC. Significantly greater amounts of phenolics were recovered from leaves than roots. There were significant qualitative and quantitative differences between the two sampling times. Compared to the control treatment, strain CS-20 alone significantly altered (usually increasing) the ferulic, caffeic, and vanillic acid contents, and concentrations of four unidentified phenolic compounds recovered from leaves and roots. In another experiment, tomato seedlings growing in sterile sand were drenched with spores of strain CS-20 the day before treating them with varying concentrations of spores of the pathogen for 24 or 72 h. Plant tissue was collected and phenolic compounds were extracted. The amount of pathogen present did not significantly affect the plant phenolic response to the presence of strain CS-20. This work demonstrates that tomato responds within 24 h to the presence of the biocontrol strain CS-20 by alterations in secondary metabolism that are typical of resistance responses in tomato.