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Distinct Defenses Induced in Wheat Against Powdery Mildew by Acetylated and Nonacetylated Oligogalacturonides

First, second, third, eighth, and ninth authors: Université Lille Nord de France, F-59000 Lille, Unité de Chimie Environnementale et Interactions sur le Vivant, GIS PhyNoPi, Université du Littoral Côte d'Opale, 17 avenue Blériot, BP 699, F-62228 Calais cedex, France; fourth and seventh authors: Laboratoire des Polysaccharides Microbiens et Végétaux, Université de Picardie Jules Verne, Avenue des Facultés, le Bailly, F-80025 Amiens cedex, France; fifth author: Arvalis-Institut du Végétal, Station Expérimentale, F-91720 Boigneville cedex, France; and sixth author: LaSalle Beauvais, GIS PhyNoPi, rue P. Waguet, BP 30313, F-60026 Beauvais cedex, France.

In wheat, little is known about disease resistance inducers and, more specifically, about the biological activities from those derived from endogenous elicitors, such as oligogalacturonides (OGAs). Therefore, we tested the ability of two fractions of OGAs, with polymerization degrees (DPs) of 2–25, to induce resistance to Blumeria graminis f. sp. tritici and defense responses in wheat. One fraction was unacetylated (OGAs–Ac) whereas the second one was 30% chemically acetylated (OGAs+Ac). Infection level was reduced to 57 and 58% relative to controls when OGAs–Ac and OGAs+Ac, respectively, were sprayed 48 h before inoculation. Activities of various defense-related enzymes were then assayed in noninoculated wheat leaves infiltrated with OGAs. Oxalate oxidase, peroxidase, and lipoxygenase were responsive to both OGAs–Ac and OGAs+Ac, which suggests involvement of reactive oxygen species and oxilipins in OGAs-mediated responses in wheat. In inoculated leaves, both fractions induced a similar increase in H₂O₂ accumulation at the site of fungal penetration. However, only OGAs+Ac led to an increase in papilla-associated fluorescence and to a reduction of formed fungal haustoria. Our work provides the first evidence for elicitation and protection effects of preventive treatments with OGAs in wheat and for new properties of acetylated OGAs.

Additional keywords: induced resistance, Triticum aestivum.