Seleção de rizobactérias como promotoras de crescimento e indutoras de resistência sistêmica em feijoeiro / Selection of rhizobacteria as growth-promoters and inducers of systemic resistance in bean

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Two hundred rhizobacteria obtained from rhizosphere and rhizoplane of healthy looking bean plants were investigated for their ability to promote growth in bean plants, increase grain yield and induce systemic resistance against leaf pathogens. In growth-promoting assays, bean seeds (Ouro Negro) were microbiolized with a propagule suspension and next sown under greenhouse conditions for quantification of growth parameters. In the laboratory conditions each isolate was also tested, for its ability to solublize phosphate and produce phosphatases. The isolate RP 28 solubilized phosphate in culture medium, but isolate RP 31 produced higher activity of phosphatases than RP28. When the root colonization bioassay was performed by seed microbiolization, eight out of 200 isolates colonized roots, which did not include the isolates selected previously. Based on in vitro and in vivo assays, isolates UFV-RP 28 and UFV- RP 31 were selected to test for plant growth promotion. Despite growth promotion detected in the greenhouse trials, no yield increased was observed in field experiments. The antagonistic potentiality of all rhizobacteria was investigated in vitro in order to verify whether they would show direct antagonism against canopy pathogens. Only four isolates showed direct antibiosis against Xanthomonas axonopodis pv. phaseoli but not against other pathogens tested. The selected isolates did not show any antagonistic activity against pathogens. All the three isolates produced siderophore but not chitinases. Induction of systemic resistance in plants microbiolized with isolate UFV-RP 48, UFV-RP 53 or UFV-RP 63 was determined in greenhouse experiments with use of Xanthomonas axonopodis pv. phaseoli as the challenging pathogen. These isolates in the previous testes were efficient for reducing disease severity. In the repeated inoculation, isolate RP 53 proved to be most efficient by reducing disease severity by 50% and was selected for field trial. Two experiments were done under field conditions. In the first, the severity of naturally occurring angular leaf spot (Phaeoisariopsis griseola) and rust (Uromyces appendiculatus), was 30% lower on plants originating from from seeds microbiolized with the rhizobacterium UFV-RP 53. In a second experiment, angular leaf spot did not appear, and the severity of rust was 43% lower on plants originating from UFV-RP 53 treated plants. Considering the spatial separation between the microbial components of the interaction, the multiplicity of protection as well as the lack of direct antagonism against investigated pathogens, the observed biocontrol may be a situation of induced resistance. Because of the good performance of isolate UFV-RP 53 as biocontrol agent, including to under field conditions, it was identified by both fatty-acid analysis and 16S rRNA sequencing as Pseudomonas putida.

ASSUNTO(S)

beans resistance induction rhizobacteria rizobactéria indução de resistência feijão fitopatologia

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