Efeito da quitosana no controle de doenças e no desenvolvimento de plântulas de videira (Vitis vinifera)

Abstract

This research aimed to evaluate different chitosan concentrations on the control of grapevines fungal diseases and vegetative development of cv. Cabernet Sauvignon and Merlot. The experiments were carried out in Departamento de Agronomia da Universidade Estadual do Centro-Oeste do Paraná. In 2007, the experiment consisted in cuttings planted in vases, with sand as substrate and kept in greenhouse under misty system irrigation. After sixty days, chitosan was sprayed, in 12 days intervals. Chitosan concentrations were 0, 20, 40 and 80 mg L-1. Plants were inoculated in a suspension of Plasmopora viticola (1x106 sporangia mL-1) spores, seven days after the ninth chitosan spray. As the first symptoms onset, mildew severity was evaluated on 8 previously identified leaves per plant, using a diagrammatic scale of grades from one to twelve, which corresponds to 0 % to 100 % of injuried foliar area. Evaluation was done 28 days after inoculation. There was a negative linear effect on chitosan doses for cv. Cabernet Sauvignon. Decrease was 76.8 % on the highest chitosan dose (160 mg L -1). In the following year experiments, pre-rooted cuttings planted in vases containing substrate (sand and Plantmax®) were used, and cuttings were sprayed each seven days with aqueous solutions and the following chitosan concentrations: 0, 20, 40, 80 and 160 mg L -1. Half of total number of plants was inoculated with Plasmopara viticola spores suspension, 48 hours after the second chitosan spray. As the first symptoms onset, ten days after inoculation, severity evaluations were performed each two days. Chitosan dose of 160 mg L-1 reduced the mildew severity by 70.24 % and 79.1 % in cultivars Merlot and Cabernet Sauvignon, respectively. Sixty days after planting, plants that were not inoculated, were evaluated for the following variables: dry roots and leaves weight, roots length and foliar area. There were not significant differences among treatments in plant development. Other experiments, in vitro and in field conditions were carried out on the same chitosan concentrations. The mycelial growth test was conducted to Elsinoe ampelina, Botryosphaeria sp and Glomerella cingulata and the germination test for Elsinoe ampelina e Plasmopara viticola. There was a decrease in E. ampelina mycelial growth.The highest chitosan concentration (160 mg L-1) decreased in 57 % the fungus developmen, 192 hours after incubation. There was a development decrease by 30 and 40 %, for Botryosphaeria sp and Glomerella cingulata, 48 hours after incubation, respectively for the same chitosan concentration. In germination tests, the 160 mg L-1 chitosan dose reduced the spore germination of E. ampelina in approximately 98 % and 60 % for P. viticola, not differing from treatments with Bordeaux mixture and mancozeb. In field conditions experiments, the highest chitosan doses (80 and 160 mg L-1) presented a decrease in anthracnose severity among 93 and 81 %. For downy mildew, 160 mg L-1 concentration decreased the disease by approximately 81 %. It was possible to conclude that chitosan has a great potential in grapevines fungal diseases control.