Controle biológico de Alternaria dauci com Bacillus pumilus e Bacillus subtilis em sementes de cenoura
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Data
2021-12-16
Autores
Riceto, Mariane Pereira
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Universidade Estadual Paulista (Unesp)
Resumo
A queima-das-folhas na cultura da cenoura pode ser causada por um complexo etiológico, entre os quais se destaca o fungo A. dauci. Este patógeno é transmitido por sementes infectadas, podendo reduzir a germinação e vigor, ressaltando a importância da utilização de sementes isentas deste fungo. O gênero Bacillus tem sido investigado pela sua habilidade de controlar fitopatógenos, característica concedida principalmente ao mecanismo de antibiose. Seu emprego possui o intuito de minimizar os efeitos negativos do uso de produtos químicos e aumentar a produção de alimentos de melhor qualidade, propiciando, assim, o desenvolvimento de uma agricultura alternativa e/ou sustentável. Diante do exposto, o presente trabalho teve como objetivo verificar a viabilidade do emprego das bactérias B. pumilus e B. subtilis como alternativa de controle de A. dauci em sementes de cenoura, avaliando a ação in vitro destas antagonistas sobre o patógeno e os efeitos de seu emprego no tratamento das sementes sobre a qualidade sanitária e fisiológica das sementes tratadas, e no desenvolvimento inicial das plântulas. Inicialmente, foi avaliado o efeito in vitro de B. subtilis (linhagem QST 713) e B. pumilus (linhagem QST 2808) sobre o A. dauci por meio do teste de pareamento em meio de cultura, em placas de Petri. Em seguida, sementes de cenoura cultivar Brasília foram tratadas com as espécies de Bacillus, para averiguar o efeito dos antagonistas in vivo. Sementes tratadas com fungicida à base de ditiocarbamato, sementes inoculadas não tratadas e sementes não inoculadas não tratadas compuseram os demais tratamentos. Após os tratamentos, as sementes foram avaliadas quanto à qualidade sanitária, pelo método do papel filtro, e ao potencial fisiológico pelos testes de primeira contagem de germinação (PCG - vigor) e germinação (G). Para avaliar o efeito dos tratamentos no desenvolvimento das plântulas, em casa-de-vegetação, foram avaliados o índice de velocidade de emergência (IVE), comprimento de raiz e de parte aérea, e massa fresca e seca de raiz e parte aérea. No teste in vitro, não houve diferença estatística entre os tratamentos para a formação do halo de inibição, mostrando que os isolados de B. subtilis e B. pumilus empregados têm pouco e/ou nenhum efeito antagonista contra A. dauci. O tratamento biológico com B. subtilis e B. pumilus diminuiu a incidência do patógeno nas sementes de cenoura. Com relação à qualidade fisiológica, B. subtilis não interferiu na germinação e vigor (PCG) das sementes, mas B. pumilus apresentou efeitos distintos sobre estas variáveis nos dois ensaios, interferindo negativamente na PCG e germinação no primeiro ensaio. O tratamento biológico das sementes não interferiu no desenvolvimento das plântulas nos experimentos em casa-de-vegetação. Os resultados indicam que B. subtilis tem potencial de emprego no manejo de A. dauci nas sementes de cenoura. Embora B. pumilus tenha sido eficiente na redução do patógeno nas sementes, os efeitos deste antagonista na germinação e vigor sugerem a necessidade de mais investigações para a sua recomendação na microbiolização de sementes de cenoura.
Carrots leaf blight can be caused by an etiological complex, which includes Alternaria dauci fungus. Infected seeds transmit this pathogen, which can reduce germination and vigor, highlighting the importance of using seeds free of this fungus. The genus Bacillus has been investigated for its ability to control phytopathogens, a characteristic attributed mainly to the mechanism of antibiosis. Its use seeks to minimize the negative effects of chemical products and increase the production of better quality food, thus providing the development of an alternative and/or sustainable agriculture. Regarding the aforementioned, the present study aimed to verify the use of B. pumilus and B. subtilis as an alternative to control A. dauci in carrot seeds, by the evaluation of those antagonists in vitro action on the pathogen, the effects of their use in seed treatments on the sanitary and physiological quality of the treated seeds, and on the initial development of the seedlings. Initially, the in vitro effects of B. subtilis (QST 713 strain) and B. pumilus (QST 2808 strain) on A. dauci were evaluated through the pairing test in culture medium, in Petri dishes. Then, cultivar Brasília carrot seeds were treated with Bacillus species, to investigate the effect of antagonists in vivo. Seeds treated with a dithiocarbamate-based fungicide, untreated inoculated seeds and untreated uninoculated seeds composed the other treatments. After the treatments, seeds were evaluated for sanitary quality, with the filter paper method, and for the physiological potential, with the first germination count (PCG - vigor) and germination (G) tests. In order to evaluate the treatments effect on seedling development, emergence speed index (IVE), root and shoot length, as well as root and shoot fresh and dry mass were evaluated in greenhouse experiments. There was no statistical difference between the treatments for the inhibition halo in in vitro tests, showing that the B. subtilis and B. pumilus isolates tested have little and/or no antagonistic effect against A. dauci. Biological treatment with B. subtilis and B. pumilus reduced the incidence of the pathogen on carrot seeds. Concerning seeds physiological quality, B. subtilis did not interfere with seeds germination and vigor (PCG), but B. pumilus had different effects on these variables in the two assays, presenting negative interference on PCG and germination in the first assay. The biological treatment of the seeds did not interfere in seedlings development in greenhouse experiments. The results indicate that B. subtilis has potential for use in the management of A. dauci in carrot seeds. Although B. pumilus was efficient in reducing the pathogen incidence in seeds, the effects of this antagonist on germination and vigor suggest that further investigations are necessary for its recommendation in carrot seeds microbiolization.
Carrots leaf blight can be caused by an etiological complex, which includes Alternaria dauci fungus. Infected seeds transmit this pathogen, which can reduce germination and vigor, highlighting the importance of using seeds free of this fungus. The genus Bacillus has been investigated for its ability to control phytopathogens, a characteristic attributed mainly to the mechanism of antibiosis. Its use seeks to minimize the negative effects of chemical products and increase the production of better quality food, thus providing the development of an alternative and/or sustainable agriculture. Regarding the aforementioned, the present study aimed to verify the use of B. pumilus and B. subtilis as an alternative to control A. dauci in carrot seeds, by the evaluation of those antagonists in vitro action on the pathogen, the effects of their use in seed treatments on the sanitary and physiological quality of the treated seeds, and on the initial development of the seedlings. Initially, the in vitro effects of B. subtilis (QST 713 strain) and B. pumilus (QST 2808 strain) on A. dauci were evaluated through the pairing test in culture medium, in Petri dishes. Then, cultivar Brasília carrot seeds were treated with Bacillus species, to investigate the effect of antagonists in vivo. Seeds treated with a dithiocarbamate-based fungicide, untreated inoculated seeds and untreated uninoculated seeds composed the other treatments. After the treatments, seeds were evaluated for sanitary quality, with the filter paper method, and for the physiological potential, with the first germination count (PCG - vigor) and germination (G) tests. In order to evaluate the treatments effect on seedling development, emergence speed index (IVE), root and shoot length, as well as root and shoot fresh and dry mass were evaluated in greenhouse experiments. There was no statistical difference between the treatments for the inhibition halo in in vitro tests, showing that the B. subtilis and B. pumilus isolates tested have little and/or no antagonistic effect against A. dauci. Biological treatment with B. subtilis and B. pumilus reduced the incidence of the pathogen on carrot seeds. Concerning seeds physiological quality, B. subtilis did not interfere with seeds germination and vigor (PCG), but B. pumilus had different effects on these variables in the two assays, presenting negative interference on PCG and germination in the first assay. The biological treatment of the seeds did not interfere in seedlings development in greenhouse experiments. The results indicate that B. subtilis has potential for use in the management of A. dauci in carrot seeds. Although B. pumilus was efficient in reducing the pathogen incidence in seeds, the effects of this antagonist on germination and vigor suggest that further investigations are necessary for its recommendation in carrot seeds microbiolization.
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Palavras-chave
Controle alternativo, Daucus carota, Microbiolização de sementes, Patologia de sementes, Queima-das-folhas da cenoura, Alternative control, Daucus carota, Seed microbiolization, Seed pathology, Carrot leaf blight