Chitosan as an option to control mildew in the sustainable vinegrowing

The aim of this study was to evaluate different concentrations of chitosan on the severity of mildew and the germination of Plasmopara viticola, in addition to its effect on vegetative growth of grapevines cv. Cabernet Sauvignon and Merlot. Two experiments were conducted. In the first vine cuttings were planted in pots with Plantmax (R) and sand 1:1 (v:v) and maintained in a greenhouse under intermittent mist. Every seven days were sprayed with aqueous solutions of chitosan at concentrations of 0, 20, 40, 80 and 160 mg L-1. The leaves were inoculated with sporangia of P. viticola 48 hours after the second application of chitosan. The first symptoms appeared ten days after inoculation, and severity ratings were performed every two days. The concentration of 160 mg L-1 of chitosan decreased the severity of downy mildew in 70.2 % and 79.1% in cv. Merlot and Cabernet Sauvignon, respectively. Sporangial germination tests were also conducted. The highest concentration of chitosan (160 mg L-1) inhibited by 50 % germination of P. viticola after 24 hours. In the second experiment, cuttings, pre-rooted, were obtained and handled as the previous experiment. After 60 days in a greenhouse, we evaluated the following variables: mass of roots and leaves, root length and leaf area. There was no significant difference between treatments for the variables related to plant development.