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Carbohydrate fractionation and profiles in the rachis of wheat varieties susceptible and resistant to Fusarium graminearum

Hadinezhad, M., Watson, E.M., Tosh, S.M., Brummer, Y. and Miller, S.S. 2016. Carbohydrate fractionation and profiles in the rachis of wheat varieties susceptible and resistant to Fusarium graminearum. Poster presented at 8th Canadian Workshop on Fusarium Head Blight, Nov.20-22, 2016, Ottawa, ON, Canada.

Abstract

Fusarium head blight (FHB) is a serious disease of wheat caused by Fusarium graminearum which affects both yield and quality of wheat. Plant resistance to pathogens is comprised of a complex network of constitutive and inducible defensive barriers. The cell wall of the wheat rachis is the first major barrier that pathogens must overcome to successfully colonize plant tissues. Therefore, the main objective of this study was to determine the cell wall composition of the rachis in two wheat varieties: Chinese Spring (CS) a susceptible variety, and CS-7EL, an addition line of Chinese Spring that carries a fragment of the long arm of chromosome 7E of Thinopyrum elongatum, which confers resistance to FHB. Both lines were point inoculated at anthesis, and the heads collected at day 4. Sequential gravimetric analysis was conducted to fractionate the rachis, and the carbohydrate profiles of free sugar, soluble polysaccharides, and insoluble polysaccharides were evaluated by HPLC. Cellulose, hemicellulose, and lignin were the three major structural components of the rachis with 33.93 ± 1.6 %, 29.62 ± 1.4 %, and 12.87 ± 1.50 % (w/w), respectively. The main sugars in the ethanol fraction for both varieties were sucrose, glucose, and fructose, while the soluble and insoluble polysaccharides comprised mainly glucose followed by xylose and small amounts of arabinose. Although the glucose level in the insoluble polysaccharide fraction showed no significant difference in the control treatment for both varieties, the fungus inoculated treatment showed significantly higher glucose for CS-7EL compared to CS. The same trend was obtained for sucrose content in the ethanol fraction. However, glucose and fructose in CS-7EL were higher than in CS, both in control and inoculated treatments. These results suggest that sucrose in the free form is the preferred substrate for Fusarium. Also, the cellulose/hemicellulose polysaccharides of the rachis in CS are degraded relatively easily by the fungus, but the cell wall presents a much stronger barrier in CS-7EL.

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