Microbiological properties of soils are sensitive to changes provided by organic cultivation of banana 'BRS Princesa' in the semi-arid region

Soil microbiota has a key role in the dynamics of natural and agro-ecosystems and is sensitive to changes in these environments. This study evaluated changes in the microbiological properties of soils under an organic production system of banana 'BRS Princesa' (Musa spp.). The experimental design consisted of completely randomized blocks, with four replications. Treatments consisted of 1) soil cover with green manure and agricultural gypsum at a dose of 2,820 kg ha−1, 2) soil cover with green manure without gypsum application, 3) soil cover with weeds and agricultural gypsum at a dose of 2,820 kg ha−1, 4) soil cover with spontaneous plants without gypsum application, and two controls: 5) soil under native Caatinga and 6) soil under regenerating forest (capoeira). The evaluated properties were ß-glucosidase, arylsulfatase, acid phosphatase, fluorescein diacetate hydrolysis activities (FDA), carbon and phosphorus contents in microbial biomass, basal soil respiration, microbial and metabolic quotients, and arbuscular mycorrhizal fungi spore density. Soil samples were collected from the 0­0.20m depth layer in two seasons. No parameter could distinguish the treatments. Spontaneous plants provided conditions equivalent to those under green manure. Agricultural gypsum application also did not influence the microbial biomass and microbiota activity, in the analyzed soil depth. However, ß-glucosidase and arylsulfatase activities, the carbon content in microbial biomass, and metabolic and microbial quotients were sensitive to land-use changes and could distinguish areas under organic cultivation from those under native vegetation. Therefore, these properties can be considered good indicators for monitoring the quality of these soils. Furthermore, microbial communities of soils under organic cultivation responded with arylsulfatase activity corresponding to that found in soils under regenerating forest, which may indicate that organic management tends to provide the microbiota with a condition similar to that found under situations that are little disturbing to edaphic living.(AU)

Bioassay on banana rhizome discs for selecting bacteria antagonistic to Fusarium oxysporum f. sp. cubense / Bioensaio em discos de rizomas de bananeiras para a seleção de bactérias antagonistas a Fusarium oxysporum f. sp. cubense

Detached plant organs are alternative materials to in vitro tests for selecting biocontrol agents. On the other hand, the use of scales to quantify injured areas can generate inconsistent results. Rhizospheric and endophytic bacteria were selected as growth inhibitors of Fusarium oxysporum f. sp. cubense (Foc), the causal agent of Panama disease of banana. For this, rhizome discs were treated with 200 µL of antagonist suspension (109 CFU mL−¹) and inoculated with the pathogen. The material was placed in plastic gerbox boxes and incubated in BOD at 25 °C for 12 days. Afterward, the area of rhizome discs (mm²) colonized by Foc was quantified by digital images. The assay was set up in a completely randomized design, with four replications and three discs per replication. The control consisted of untreated and inoculated discs. The results showed the efficiency of this method in selecting the biological control agent, as the 26 isolates were group into five different clusters, with isolates belonging to four of these groups (from '1' to '4') being able to reduce Foc colonization. Isolates 520EB, 993EB, and 531EB had the highest potential for inhibition, with areas of 343.3, 344.1, 364.8 mm², respectively, promoting inhibition ranging from 53 to 56 % of the colonized area compared to the control (782.6 mm²).

O emprego de órgãos vegetais destacados é uma alternativa aos testes in vitro para seleção de agentes de biocontrole. Por outro lado, o uso de escalas para quantificação de área lesionada pode gerar resultados inconsistentes. Bactérias rizosféricas e endofíticas foram selecionadas como inibidoras do crescimento de Fusarium oxysporum f. sp. cubense (Foc), agente causal do mal-do-Panamá da bananeira. Para tanto, discos de rizoma foram tratados com 200 µL de suspensão dos antagonistas (109 UFC mL-¹) e inoculados com patógeno. O material foi disposto em caixas plásticas tipo gerbox e incubado em BOD a 25 ºC, por doze dias. Após, a área dos discos de rizoma (mm²) colonizada por Foc dos discos foi quantificada por meio de imagens digitais. O ensaio foi montado em delineamento inteiramente casualizado, com quatro repetições e três discos por repetição. Discos não tratados e inoculados compuseram o controle. Com base nos resultados obtidos, foi possível verificar a eficiência do método na seleção de agente de controle biológico, uma vez que foi possível o agrupamento dos 26 isolados utilizados em cinco clústeres distintos, sendo que isolados pertencentes a quatro destes grupos (do '1' a '4') foram capazes de proporcionar a redução da colonização por Foc. Os isolados com maior potencial de inibição foram520EB, 993EB e 531EB com 343,3, 344,1, 364,8 mm2, respectivamente, promovendo inibição variando de 53 a 56 % da área colonizada quando comparados com ao controle (782,6 mm²).

Bioassay on banana rhizome discs for selecting bacteria antagonistic to Fusarium oxysporum f. sp. cubense / Bioensaio em discos de rizomas de bananeiras para a seleção de bactérias antagonistas a Fusarium oxysporum f. sp. cubense

Detached plant organs are alternative materials to in vitro tests for selecting biocontrol agents. On the other hand, the use of scales to quantify injured areas can generate inconsistent results. Rhizospheric and endophytic bacteria were selected as growth inhibitors of Fusarium oxysporum f. sp. cubense (Foc), the causal agent of Panama disease of banana. For this, rhizome discs were treated with 200 µL of antagonist suspension (109 CFU mL−¹) and inoculated with the pathogen. The material was placed in plastic gerbox boxes and incubated in BOD at 25 °C for 12 days. Afterward, the area of rhizome discs (mm²) colonized by Foc was quantified by digital images. The assay was set up in a completely randomized design, with four replications and three discs per replication. The control consisted of untreated and inoculated discs. The results showed the efficiency of this method in selecting the biological control agent, as the 26 isolates were group into five different clusters, with isolates belonging to four of these groups (from '1' to '4') being able to reduce Foc colonization. Isolates 520EB, 993EB, and 531EB had the highest potential for inhibition, with areas of 343.3, 344.1, 364.8 mm², respectively, promoting inhibition ranging from 53 to 56 % of the colonized area compared to the control (782.6 mm²).(AU)

O emprego de órgãos vegetais destacados é uma alternativa aos testes in vitro para seleção de agentes de biocontrole. Por outro lado, o uso de escalas para quantificação de área lesionada pode gerar resultados inconsistentes. Bactérias rizosféricas e endofíticas foram selecionadas como inibidoras do crescimento de Fusarium oxysporum f. sp. cubense (Foc), agente causal do mal-do-Panamá da bananeira. Para tanto, discos de rizoma foram tratados com 200 µL de suspensão dos antagonistas (109 UFC mL-¹) e inoculados com patógeno. O material foi disposto em caixas plásticas tipo gerbox e incubado em BOD a 25 ºC, por doze dias. Após, a área dos discos de rizoma (mm²) colonizada por Foc dos discos foi quantificada por meio de imagens digitais. O ensaio foi montado em delineamento inteiramente casualizado, com quatro repetições e três discos por repetição. Discos não tratados e inoculados compuseram o controle. Com base nos resultados obtidos, foi possível verificar a eficiência do método na seleção de agente de controle biológico, uma vez que foi possível o agrupamento dos 26 isolados utilizados em cinco clústeres distintos, sendo que isolados pertencentes a quatro destes grupos (do '1' a '4') foram capazes de proporcionar a redução da colonização por Foc. Os isolados com maior potencial de inibição foram520EB, 993EB e 531EB com 343,3, 344,1, 364,8 mm2, respectivamente, promovendo inibição variando de 53 a 56 % da área colonizada quando comparados com ao controle (782,6 mm²).(AU)