First and second authors: Département de phytologie-FSAA, Université Laval, Québec, Qc, G1K 7P4; and third author: Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, MB, R3T 2M9
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Accepted for publication 25 September 2002.
Silicon (Si) amendments in the form of exogenously supplied nutrient solution or calcium silicate slag protect wheat plants from powdery mildew disease caused by the fungus Blumeria graminis f. sp. tritici. The most striking difference between Si- and Si+ plants challenged with B. graminis f. sp. tritici was the extent of epidermal cell infection and colonization by B. graminis f. sp. tritici. Histological and ultrastructural analyses revealed that epidermal cells of Si+ plants reacted to B. graminis f. sp. tritici attack with specific defense reactions including papilla formation, production of callose, and release of electron-dense osmiophilic material identified by cytochemical labeling as glycosilated phenolics. Phenolic material not only accumulated along the cell wall but also was associated with altered integrity of haustoria in a manner similar to localized phytoalexins as reported from other pathosystems. These results strongly suggest that Si mediates active localized cell defenses against B. graminis f. sp. tritici attack.
© 2003 The American Phytopathological Society