Chitosan in induced resistance : more chances than limits or vice versa?

The effectiveness of chitosans (CHTs), deacetylated chitin derivatives, as plant resistance inducers depends on a number of variables, such as the molecular weight (MW) and the deacetylation degree (DD) of the oligomers/polymers, the solvent, the pathosystem and the mode of administration. All these aspects are briefly examined and discussed with the aim of giving useful advices for succesfull application of CHTs, particularly to control virus diseases