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RESENDE, Mário Lúcio V. et al. Selection of plant extracts to induce resistance and activate defense responses in cocoa against witches' broom disease. Fitopatol. bras. [online]. 2007, vol.32, n.3, pp. 213-221. ISSN 0100-4158. http://dx.doi.org/10.1590/S0100-41582007000300005.
The objective of this study was to find new inducers of resistance against witches' broom disease (Crinipellis perniciosa) of cocoa (Theobroma cacao), with higher or equal efficacy to that conferred by the standard inducer acibenzolar-S-methyl and to study possible defense responses activated in cocoa by these more efficient elicitors. Extracts from several plants were tested, mainly those from native plants from the savannah of Minas Gerais State, as well as extracts from cultivated plants. It was verified that aqueous extracts from "lobeira" (Solanum lycocarpum) tree with symptoms of witches' broom induced protection of cocoa seedlings at similar levels as that conferred by ASM. The aqueous and boiled extract from "lobeira", here named VLA, was not toxic in vitro: in fact, it promoted C. perniciosa growth on PDA medium. The activities of pathogenesis-related proteins chitinase and b-1,3- glucanase stimulated by VLA and ASM were assessed and it was verified that both treatments induced higher activities of peroxidase, chitinase and b-1,3-glucanase in cocoa seedlings, compared to the respective controls, from 4 to 18 days after spraying (DAS). The lignin content also increased in plants treated with VLA or ASM, mainly at 18 DAS.
Keywords : Induced resistance; Theobroma cacao; Solanum lycocarpum; acibenzolar-S-methyl (ASM); pathogenesis-related proteins; lignin.