Potencial de ação de compostos como protetivos e sanitizantes contra o fitopatógeno Xanthomonas citri subsp. citri, causador do cancro cítrico
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Data
2019-02-28
Autores
Zamuner, Caio Felipe Cavicchia
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Universidade Estadual Paulista (Unesp)
Resumo
A citricultura constitui uma importante atividade econômica no país, com o Brasil sendo o maior produtor de laranja doce no mundo. A produção é ameaçada pelo cancro cítrico asiático, uma doença severa que traz grande prejuízo e leva a necessidade do controle de seu agente causador, a bactéria Gram-negativa Xanthomonas citri subsp. citri (Xac). Atualmente não há nenhuma medida curativa para os pomares e a opção é o manejo integrado para evitar o avanço da doença. O único controle químico utilizado no presente é a aplicação de compostos a base de cobre, os quais trazem riscos de contaminação ao solo e de mananciais de água. Desta forma, estratégias alternativas de controle são essenciais para manter a citricultura brasileira competitiva no mercado. Compostos derivados do metabolismo vegetal tais como os flavonoides, ácido fenólicos e terpenóides são classes de substâncias com um grande potencial antimicrobiano. Nesse contexto, foi avaliada a ação anti-Xac de compostos híbridos de chalcona, ésteres do ácido vanílico e os monoterpenóides Timol e Carvacrol. No caso dos híbridos de pirazinamida-chalconas, não houve atividade antimicrobiana constatada contra Xac. Para os vanilatos, os compostos de cadeia lateral de 5 até 8 carbonos apresentaram ação anti-Xac, com atividade bacteriostática. Timol e Carvacrol mostraram atividade anti-Xac, uma vez que foram bactericidas a 200 μg.mL-1. Estes terpenóides foram avaliados quanto ao seu modo de ação e apresentaram atividade na permeabilização da membrana de Xac, não agindo sobre a divisão/segregação ou causando danos ao DNA. Timol e Carvacrol apresentam baixa fitotoxiciade em sementes de Lactuca sativa até 100 μg.mL-1. Os ensaios protetivos em mudas de Citrus sinensis não indicaram ação mais eficaz para Timol e Carvacrol frente ao oxicloreto de cobre.
Citriculture has great importance to Brazil`s economy, with the country occupying the post of the largest sweet orange producer in the world. This production is threatened by Asiatic citrus canker, a crop disease which causes great losses in production and fruit quality. Because of these problems, there is a need to manage its causal agent – the Gram-negative bacteria Xanthomonas citri subps. citri (Xac). Nowadays there are no curative measure to surpass the disease in the orchards and the only option is the integrated management to avoid its spread. The only chemical control used in this strategy is based on copper, which is associated with soil and water springs contamination. For that reason, new alternative control strategies become essential to maintain the Brazilian citriculture competitive in the market. Compounds derived from plants metabolism such as flavonoids, phenolic acids and terpenoids are interesting substances with antimicrobial proprieties. In this context, we evaluated the anti-Xac action of hybrid chalcone compounds, vanillic acid esters and monoterpenoids (Thymol and Carvacrol). The pyrazinamide-chalcone hybrids showed no antimicrobial activity against Xac. In the case of the vanillic acid esters, synthetic compounds with a side chain structure composed of 5 to 8 carbons presented an bacteriostatic anti-Xac activity. Compounds Thymol and Carvacrol also showed anti-Xac action, once this compounds were bactericidal at 200 μg.mL-1. These terpenoids were evaluated for its mode of action in Xac and showed action in the membrane permeabilization, not affecting cell division/segregation nor damaging DNA. Furthermore, Thymol and Carvacrol presented low phytotoxicity until 100 μg.mL-1 in Lactuca sativa seeds. Protective assays in Citrus sinensis did not indicate a great efficiency for this monoterpenoids when compared to the commercial product based on copper oxychloride. Nevertheless, considering the promising antimicrobial activity found against Xac for Thymol and Carvacrol, it may be interesting compounds for further developments in applied formulations.
Citriculture has great importance to Brazil`s economy, with the country occupying the post of the largest sweet orange producer in the world. This production is threatened by Asiatic citrus canker, a crop disease which causes great losses in production and fruit quality. Because of these problems, there is a need to manage its causal agent – the Gram-negative bacteria Xanthomonas citri subps. citri (Xac). Nowadays there are no curative measure to surpass the disease in the orchards and the only option is the integrated management to avoid its spread. The only chemical control used in this strategy is based on copper, which is associated with soil and water springs contamination. For that reason, new alternative control strategies become essential to maintain the Brazilian citriculture competitive in the market. Compounds derived from plants metabolism such as flavonoids, phenolic acids and terpenoids are interesting substances with antimicrobial proprieties. In this context, we evaluated the anti-Xac action of hybrid chalcone compounds, vanillic acid esters and monoterpenoids (Thymol and Carvacrol). The pyrazinamide-chalcone hybrids showed no antimicrobial activity against Xac. In the case of the vanillic acid esters, synthetic compounds with a side chain structure composed of 5 to 8 carbons presented an bacteriostatic anti-Xac activity. Compounds Thymol and Carvacrol also showed anti-Xac action, once this compounds were bactericidal at 200 μg.mL-1. These terpenoids were evaluated for its mode of action in Xac and showed action in the membrane permeabilization, not affecting cell division/segregation nor damaging DNA. Furthermore, Thymol and Carvacrol presented low phytotoxicity until 100 μg.mL-1 in Lactuca sativa seeds. Protective assays in Citrus sinensis did not indicate a great efficiency for this monoterpenoids when compared to the commercial product based on copper oxychloride. Nevertheless, considering the promising antimicrobial activity found against Xac for Thymol and Carvacrol, it may be interesting compounds for further developments in applied formulations.
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Palavras-chave
Cancro cítrico, Xanthomonas, Citricultura, Antimicrobianos, Citrus canker, Citriculture, Antimicrobials