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EnglishThe cotton plant (Gossypium hirsutum) is affected by several diseases of economic importance, among them root-knot nematode (Meloidogyne incognita races 3 and 4). Methods to control this disease include the application of nematicides, solarization, deep plowing, crop rotation and use of antagonistic microorganisms. Among species of Bacillus, there are strains that act as bioregulators and antagonists of several pathogens. Tests to identify these strains are hampered by the difficulty of obtaining large populations of the pathogen and by the time of execution of the in vivo tests that should be conducted for about 90 days. The objective of this research was to compare the toxicity of B. thuringiensis strains to two nematodes, M. incognita and Caenorhabditis elegans, evaluating the possibility of using C. elegans as an indicator for the selection of strains with biocontrol potential against M. incognita. Therefore, the toxicity of nine B. thuringiensis strains on C. elegans and M. incognita was evaluated under laboratory and greenhouse conditions. Most strains toxic to C. elegans in vitro were also toxic to M. incognita, and three of them (S906, S1192, S2036) significantly reduced the populations of the two nematodes. The toxic effect of B. thuringiensis strains on C. elegans was like that reported for the same bacterial isolates on M. incognita in vivo. These results suggested that it is plausible to use C. elegans as an indicator of toxicity for selection of B. thuringiensis strains toxic to M. incognita. Key words: Biocontrol; phytonematode; root-knot nematode; rhizobacteria portuguesO algodoeiro (Gossypium hirsutum) e acometido por varias doencas de importância economica, dentre as quais a meloidoginose (Meloidogyne incognita racas 3 e 4). Entre os metodos de controle dessa doenca, destacam-se as aplicacoes de nematicidas, a solarizacao, a aracao profunda, a rotacao de culturas e o uso de microrganismos antagonistas. Dentre as especies do genero Bacillus, existem estirpes que atuam como biorreguladores e antagonistas de varios patogenos. Os testes para identificacao dessas estirpes sao prejudicados pela dificuldade de se obter grandes populacoes do patogeno e pelo tempo de execucao dos testes in vivo que devem ser conduzidos por cerca de 90 dias. Diante disso, o presente trabalho teve como objetivo comparar a toxicidade de estirpes de B. thuringiensis a dois nematoides, M. icognita e Caenorhabditis elegans, verificando a possibilidade de empregar C. elegans como indicador para a selecao de estirpes com potencial de biocontrole contra M. incognita. Para tanto, a toxicidade de nove estirpes de B. thuringiensis para C. elegans e M. incognita foi avaliada em laboratorio e em casa de vegetacao. A maioria das estirpes toxicas ao C. elegans in vitro, tambem foi toxica ao M. incognita, sendo que tres delas (S906, S1192, S2036) reduziram significativamente as populacoes dos dois nematoides. O efeito toxico apresentado pelas estirpes de B. thuringiensis contra C. elegans foram similares aos apresentados pelos mesmos isolados contra M. incognita in vivo. Esses resultados sugerem que e plausivel o uso do C. elegans como indicador de toxicidade para selecao de estirpes de B. thuringiensis toxicas a M. incognita. Palavras-chave: Biocontrole; fitonematoide; nematoide das galhas; rizobacterias

Caenorhabditis elegans as an indicator of toxicity of Bacillus thuringiensis strains to Meloidogyne incognita race 3