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Inhibition of Blumeria graminis f. sp. tritici Germination and Partial Enhancement of Wheat Defenses by Milsana

First author: Alternatech, 70, rue des Jacobins, F-80000 Amiens, France; second, sixth, and seventh authors: Laboratoire Mycologie-Phytopathologie-Environnement, Université du Littoral Côte d'Opale, B.P. 699, F-62228 Calais cedex, France; third author: Laboratoire d'Informatique et de Statistiques, Institut Supérieur d'Agriculture de Lille, 48 Boulevard Vauban, F-59046 Lille cedex, France; fourth author: Institut Supérieur d'Agriculture de Beauvais, rue Pierre Waguet, B.P. 30313, F-60026 Beauvais cedex, France; and fifth author: Laboratoire des Polysaccharides Microbiens et Végétaux CNRS FRE 2779, Université de Picardie Jules Verne, Avenue des Facultés, le Bailly F-80025 Amiens Cedex 1, France

The prophylactic efficiency of Milsana against powdery mildew was evaluated on wheat (Triticum aestivum). A single short spraying on 10-day-old plantlets reduced the infection level by 85% and two long sprayings led to the total restriction of the disease. Although microscopic studies showed that Milsana treatments enhance hydrogen peroxide accumulation at the fungal penetration site, biochemical analysis did not allow us to correlate this accumulation with the activation of several enzyme activities involved in active oxygen species (AOS) metabolism. Only lipoxygenase activity, which is involved in both AOS metabolism and lipid peroxidation, showed a 26 to 32% increase 48-h posttreatment in leaves infiltrated with Milsana. This weak effect of Milsana on wheat lipid metabolism was confirmed at the lipid peroxidation level, which surprisingly, was shown to decrease in treated plants. In order to explain the high efficacy of Milsana, the fungistatic effect on conidia germination was also examined. In planta, we showed that a Milsana treatment resulted in a higher proportion of abnormally long appressorial germ tubes, whereas in vitro, it dramatically inhibited fungal conidia germination. The partial activity of Milsana in terms of defense response induction in the wheat/powdery mildew pathosystem and its newly described direct fungistatic activity are discussed.

Additional keywords: induced resistance.