Bacillus spp. no controle biológico do complexo de doenças causadas por Fusarium-meloidogyne em algodoeiro
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Data
2021-07-12
Autores
Pacífico, Marina Guimarães
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Universidade Estadual Paulista (Unesp)
Resumo
O Brasil é o quarto maior produtor e o segundo exportador de algodão do mundo. A murcha de fusário (Fusarium oxysporum f. sp. vasinfectum - Fov) e a meloidoginose (Meloidogyne incognita raças 3 e 4 - Mi) causam sérios problemas às plantas, tanto isoladamente quanto em associação. O controle dessas doenças é difícil, oneroso e acarreta perdas de produtividade. Além do uso de variedades resistentes, uma alternativa, para ambos os patógenos, é o controle biológico, pois, além da eficiência, diminui a pressão da utilização de produtos químicos. Entre os agentes de biocontrole, Bacillus spp. têm se destacado no controle de doenças causadas por esses patógenos. O objetivo do presente trabalho foi selecionar e caracterizar isolados de Bacillus antagônicos a ambos os patógenos, bem como selecionar isolados promotores de crescimento das plantas. Para alcançar esses objetivos, foram realizados testes in vitro com 41 isolados de Bacillus (35 obtidos de algodoeiros, cinco da coleção da Embrapa Meio Ambiente e um produto comercial) quanto à caracterização bioquímica (produção de sideróforos, ácido indolacético, ácido cianídrico, catalase, solubilização de fosfato e assimilação de nitrogênio), à inibição do crescimento micelial e da germinação de esporos de Fov, e sobre a eclosão e a mortalidade de juvenis de Mi. Os isolados selecionados in vitro foram testados em casa de vegetação para verificar o potencial em controlar Fov e Mi raças 3 e 4, isolamente e com ambos os patógenos, além de ensaios para a promoção de crescimento de plantas. Os isolados selecionados na fase final foram identificados molecularmente. Para produção de ácido idolacético, assimilação de nitrogênio, sideróforos e catalase 20, 25, 23 e 21 isolados, respectivamente, apresentaram resultados positivos. Na inibição do crescimento micelial, 11 isolados apresentaram antagonismo a Fov e 15 reduziram significativamente a germinação de esporos. Onze isolados causaram mortalidade significativa de juvenis de Mi e quatro proporcionaram as menores áreas abaixo da curva de progresso da eclosão de ovos. Nesta fase foram selecionados os isolados S2527, S2545 e AP03. Esses isolados, bem como a mistura dos mesmos, foram avaliados quanto à promoção de crescimento de plantas e sobre o fator de reprodução dos nematoides. A mistura contendo os isolados AP03+S2527 promoveu o crescimento de plantas de algodão em rizotrons, aumentando a altura, o diâmetro do caule e os pesos frescos da parte aérea e do sistema radicular. Os isolados S2527, S25245 e AP03 reduziram em, aproximadamente, 76% o fator de reprodução de Mi aos 100 dias. Dessa maneira, esses isolados e suas misturas foram testados sobre o complexo Fusarium-Meloidogyne em casa-de-vegatação, sendo observado que os isolados AP03, S2545, S2527 e suas misturas foram eficientes em controlar o complexo Fusarium-Meloidogyne, com aproximadamente 56% de redução do número de ovos por planta aos 60 dias e 85% de redução do número de ovos aos 120 dias após a semeadura. Além disso, esses isolados aumentaram o número de planta que sobreviveram na presença de ambos os patógenos. Esses três isolados foram identificados como Bacillus velezensis.
Brazil is the fourth largest producer and the second exporter of cotton in the world. Fusarium wilt (Fusarium oxysporum f. sp. vasinfectum - Fov) and nematode root-knot (Meloidogyne incognita races 3 and 4 - Mi) are destructive to plants, both alone and in association. The control of these diseases is difficult, costly and leads to losses in productivity. In addition to the use of resistant varieties, an alternative, for both pathogens, is biological control, because, in addition to efficiency, it reduces the pressure of using chemical products. Among the biocontrol agents, Bacillus spp. has stood out in the control of diseases caused by these pathogens. The aim was to select and characterize the antagonistic Bacillus to both pathogens, as well as select that promote plant growth. To achieve these objectives, in vitro tests were carried out with 41 Bacillus isolates (35 obtained from cotton, five from the Embrapa Environment collection and one commercial product) for biochemical characterization (production of siderophores, indolacetic acid, hydrocyanic acid, catalase, phosphate solubilization and nitrogen assimilation), inhibition of mycelial growth and Fov spore germination, and on the hatching and mortality of Mi juveniles. The isolates selected in vitro were tested in a greenhouse to verify the potential to control Fov and Mi races 3 and 4, alone and with both pathogens, in addition to assays for the promotion of plant growth. Those selected were identified molecularly. For production of idolacetic acid, assimilation of nitrogen, siderophores and catalase 20, 25, 23 and 21 isolates, respectively, showed positive results. In the inhibition of mycelial growth, 11 isolates showed antagonism to Fov and 15 significantly reduced spore germination. Eleven isolates caused significant mortality of Mi juveniles and four provided the smallest areas below the egg hatch progress curve. In this phase, isolates S2527, S2545 and AP03 were selected. These isolates, as well as their mixture, were evaluated for the promotion of plant growth and for the nematode reproduction factor. The mixture containing the AP03+S2527 isolates promoted the growth of cotton plants in rhizotrons, increasing the height, stem diameter and fresh weight of shoots and roots. The isolates S2527, S25245 and AP03 reduced the reproduction factor of Mi by approximately 76% at 100 days. In this way, these isolates and their mixtures were tested on the Fusarium-Meloidogyne complex in greenhouse, and it was observed that the isolates AP03, S2545, S2527 and their mixtures were efficient in controlling the Fusarium-Meloidogyne complex, with approximately 56% of reduction in the number of eggs per plant at 60 days and 85% reduction in the number of eggs at 120 days after sowing. In addition, these isolates kept the plant alive longer in the presence of both pathogens. These three isolados were identied as Bacillus velezensis.
Brazil is the fourth largest producer and the second exporter of cotton in the world. Fusarium wilt (Fusarium oxysporum f. sp. vasinfectum - Fov) and nematode root-knot (Meloidogyne incognita races 3 and 4 - Mi) are destructive to plants, both alone and in association. The control of these diseases is difficult, costly and leads to losses in productivity. In addition to the use of resistant varieties, an alternative, for both pathogens, is biological control, because, in addition to efficiency, it reduces the pressure of using chemical products. Among the biocontrol agents, Bacillus spp. has stood out in the control of diseases caused by these pathogens. The aim was to select and characterize the antagonistic Bacillus to both pathogens, as well as select that promote plant growth. To achieve these objectives, in vitro tests were carried out with 41 Bacillus isolates (35 obtained from cotton, five from the Embrapa Environment collection and one commercial product) for biochemical characterization (production of siderophores, indolacetic acid, hydrocyanic acid, catalase, phosphate solubilization and nitrogen assimilation), inhibition of mycelial growth and Fov spore germination, and on the hatching and mortality of Mi juveniles. The isolates selected in vitro were tested in a greenhouse to verify the potential to control Fov and Mi races 3 and 4, alone and with both pathogens, in addition to assays for the promotion of plant growth. Those selected were identified molecularly. For production of idolacetic acid, assimilation of nitrogen, siderophores and catalase 20, 25, 23 and 21 isolates, respectively, showed positive results. In the inhibition of mycelial growth, 11 isolates showed antagonism to Fov and 15 significantly reduced spore germination. Eleven isolates caused significant mortality of Mi juveniles and four provided the smallest areas below the egg hatch progress curve. In this phase, isolates S2527, S2545 and AP03 were selected. These isolates, as well as their mixture, were evaluated for the promotion of plant growth and for the nematode reproduction factor. The mixture containing the AP03+S2527 isolates promoted the growth of cotton plants in rhizotrons, increasing the height, stem diameter and fresh weight of shoots and roots. The isolates S2527, S25245 and AP03 reduced the reproduction factor of Mi by approximately 76% at 100 days. In this way, these isolates and their mixtures were tested on the Fusarium-Meloidogyne complex in greenhouse, and it was observed that the isolates AP03, S2545, S2527 and their mixtures were efficient in controlling the Fusarium-Meloidogyne complex, with approximately 56% of reduction in the number of eggs per plant at 60 days and 85% reduction in the number of eggs at 120 days after sowing. In addition, these isolates kept the plant alive longer in the presence of both pathogens. These three isolados were identied as Bacillus velezensis.
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Palavras-chave
Controle biológico, Bacillus, Galha, Fusariose, Algodão, Biological control, Root-knot nematode, Fusarium wilt, Cotton