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Chitosan Oligomers and Copper Sulfate Induce Grapevine Defense Reactions and Resistance to Gray Mold and Downy Mildew

First, second, fifth, and sixth authors: Eco-Toxicologie, URVVC-EA 2069, Universitéde Reims, B.P. 1039, F-51687 Reims cedex 2, Franc; third author: Agrolor, CA Le Cahn 17, rue Laurent Bonnevay 54100 Nancy, Franc; and fourth author: Œnologie & Chimie Appliquée, URVVC-EA 2069, Universitéde Reims, B.P. 1039, F-51687 Reims cedex 2, France

Chitosan (CHN), a deacetylated derivative of chitin, was shown to be efficient in promoting plant defense reactions. CHN oligomers of different molecular weight (MW) and degree of acetylation (DA) triggered an accumulation of phytoalexins, trans- and cis-resveratrol and their derivatives ε-viniferin and piceid, in grapevine leaves. Highest phytoalexin production was achieved within 48 h of incubation with CHN at 200 μg/ml with an MW of 1,500 and a DA of 20% (CHN1.5/20), while oligomers with greater MW were less efficient, indicating that a specific MW threshold could be required for phytoalexin response. Treatment of grapevine leaves by highly active CHN1.5/20 also led to marked induction of chitinase and β-1,3-glucanase activities. CHN1.5/20 applied together with copper sulfate (CuSO₄) strongly induced phytoalexin accumulation. CuSO₄ alone, especially at low concentrations also elicited a substantial production of phytoalexins in grapevine leaves. Evidence is also provided that CHN1.5/20 significantly reduced the infection of grapevine leaves by Botrytis cinerea and Plasmopara viticola, and in combination with CuSO₄ conferred protection against both pathogens.

Additional keywords: elicitor, Vitis vinifera.