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 β-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 0–0.20m 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, β-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.
RESUMO A fim de se obter agentes de biocontrole para controle da antracnose em frutos de mamão em pós-colheita, buscou-se: i) selecionar bactérias epifíticas de mamoeiro antagonistas a Colletotrichum brevisporum pela produção de compostos antimicrobianos difusíveis e voláteis, quitinase e inibição da germinação de conídios; ii) quantificar a produção de biofilme pelos isolados selecionados; iii) obter uma concentração de bactérias que proporcionasse o controle da antracnose em discos de frutos; iv) avaliar a redução da severidade da doença em frutos de mamão. De 224 bactérias, 74 exibiram um mecanismo de ação contra o patógeno, 13 isolados dois mecanismos, quatro apresentaram três, e uma bactéria exibiu todos. Mediante a verificação da compatibilidade entre antagonistas, e a quantificação da formação de biofiolme, estabeleceram-se cinco “Mix” compostos por quatro isolados bacterianos. Em discos de frutos as bactérias foram avaliadas nas concentrações 106, 107 e 108 UFC mL-1. À exceção do Mix 2, os demais reduziram significativamente a antracnose nos discos quando comparados ao controle. Os “Mix” 1, 3, 5, na concentração 108 UFC mL-1 exibiram melhor desempenho reduzindo a doença em até 75 %, 89,78 % e 90,8 %, respectivamente. Os Mix 3 e 5, na concentração de 108 UFC mL-1, foram avaliados em frutos juntamente com o fungicida sintético Piraclostrobina. Não se verificou diferença significativa entre os Mix e o fungicida, que atingiu níveis de redução da doença superiores a 97 %, e as combinações com 98 %, frente ao controle não tratado.
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).
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