Controlling gray mould caused by Botrytis cinerea in cucumber plants by means of chitosan

The objective of this study was to evaluate the effects of chitosan and chitin oligomers on gray mould caused by Botrytis cinerea in cucumber plants. Almost complete inhibition of Botrytis conidia germination was found, in vitro, at 50 ppm chitosan but not with chitin oligomers at any concentrations. It was found that chitosan controlled the gray mould caused by B. cinerea (0.45 disease index) compared with control (3.5 disease index). Chitin oligomers did not show any effect (3.5 disease index). Although chitin oligomers elicited chitosanase activity by 2.4 folds and peroxidase activity by 2.0 folds and chitosan elicited their activities only by 1.9 and 0 fold, respectively; disease control was not affected. Spraying chitosan 1 h before inoculation with Botrytis conidia decreased gray mould incidence by 65%. Spraying chitosan 4 or 24 h before inoculation reduced disease development by 82% and 87%, respectively. However, spraying chitosan on the leaves 1 h after inoculation decreased gray mould only by 52%. It is concluded that although a dual mode of action was involved in the control of gray mould by chitosan, the antifungal activity of the compound was an essential factor. The induction of the defence response without the antifungal activity was not enough to suppress the disease. (C) 2002 Elsevier Science Ltd. All rights reserved.