Fosfitos no manejo do míldio da videira: eficácia e modo de ação

Abstract

The present study was aimed at evaluating alternative products, based on plant extracts, phosphorilated mannan-oligosaccharides, phosphites and acibenzolar-S-methyl (ASM) for the protection of grapevine against downy mildew, as well as the influence of these treatments on the quality of grape cultivar Merlot. Potassium phosphites and acibenzolar-S-methyl toxic effects on Plasmopara viticola an on the activation of defense enzymes peroxidase, polyphenoloxidase, chitinases, β-1,3-glucanase and on the contents of total soluble phenolics and lignin were assessed. In field trials, phosphites provided protection against downy mildew similarly to fungicides. Treatments based on phosphorylated mannan oligosaccharides, acibenzolar-S-methyl and plant extracts showed no effective control of downy mildew. Treatments did not influence the analytical quality of the berries. In glasshouse and lab trials, phosphites provided the lowest incidence of disease on leaves and had direct toxicity, inhibiting the germination of sporangia. Major activities of peroxidase, polyphenoloxidase and chitinases were detected after phosphite applications, which, in general, did not increase lignin content. ASM was not effective for the control of downy mildew on leaves and for the inhibition of germination of sporangia; however, increased the activity of peroxidase and promoted the accumulation of lignin.