Silicon induces antifungal compounds in powdery mildew-infected wheat

Most plants can defend themselves against fungal infections by natural means, which can be induced by a number of biotic and abiotic elicitors. Recently, soluble silicon (Si) has been shown to induce resistance in a number of plant species. In Si-treated wheat (Triticum aestivum) infected with powdery mildew (Blumeria graminis f.sp. tritici (Bgt)), microscopic and ultrastructural observations highlighted the presence of phenolic-like material associated with degraded powdery mildew haustoria. Since phytoalexins have never been reported in wheat, we sought to clarify the nature of the fungitoxic compounds produced within the leaves of Si-treated wheat plants infected with Bgt. In this work, TLC analyses coupled with a bioassay have revealed the differential presence of fungitoxic aglycones between Si-treated and control plants. When these fractions were analyzed by HPLC, comparative analyses of the profiles have confirmed that at least three compounds were produced in higher amounts following a Si treatment in infected plants. Fresh transverse sections of wheat leaves infected with Bgt were analyzed by fluorescence microscopy and zones of infection in Si-treated plants were characterized by intense fluorescence and collapse of conidial chains. These results tend to confirm that wheat plants fed with Si can produce phytoalexins in response to powdery mildew infection. (c) 2005 Elsevier Ltd. All rights reserved