Response to infection by Fusarium graminearum in the rachis of a resistant and a susceptible barley cultivar
Miller, S.S., Hadinezhad, M., Chabot, D. and Watson, E.M. (2016) Response to infection by Fusarium graminearum in the rachis of a resistant and a susceptible barley cultivar. Poster presented at 8th Canadian Workshop on Fusarium Head Blight, Nov.20-22, 2016, Ottawa, ON, Canada.
To evaluate the response of resistant and susceptible barley cultivars (cvs) to Fusarium head blight (FHB), structural and chemical changes were investigated in the rachis of Chevron, a resistant cv, and Chapais, a susceptible cv, after inoculation with Fusarium graminearum. Microscopy of cross sections of the rachis showed differences in severity of infection, with more fungus being visible in the vascular bundles of Chapais than in Chevron 5 days post-inoculation. In addition, the chemical composition of the cell walls in the vascular bundles of Chevron underwent changes, as evidenced by the loss of fluorescence in this tissue. Sequential gravimetric analysis was conducted to elucidate chemical changes in the rachis, followed by sugar profile analysis using HPLC-ELSD. The results showed that in all treatments, cellulose was the fraction with the highest content. In both cultivars, while the content of hemicellulose and cellulose decreased after inoculation with Fusarium compared to the mock inoculated samples, indicating some cell wall degradation by fungal enzymes, the lignin and water soluble components increased. The content of lignin in Fusarium inoculated samples of Chevron (23.2 ± 1.2 %, w/w dried rachis tissue) was significantly higher than in Chapais (12.2 ± 1.2 %), which could reflect cell wall fortification in Chevron as a defence against FHB. Sucrose was the predominant free sugar in the water soluble fraction of all treatments, however, the total content of free sugars (sucrose, glucose and fructose) was significantly higher in the Fusarium inoculated Chapais (5.3 ± 0.2 %, w/w dried rachis tissue) compared to Chevron (4.5 ± 0.2 %), suggesting greater fungal degradation of the cell wall and stored fructans in the susceptible cultivar. The sugar composition of the cellulose fraction was similar for all treatments, glucose being the main component with small amounts of xylose and fructose. However, the content of glucose was higher in the rachis of inoculated Chevron compared to Chapais, suggesting stronger cell wall structure in the resistant barley.
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