Isolation, identification, and biocontrol activity of an endophytic strain Bacillus amyloliquefaciens CGB15 from sugarcane

Abstract:

More than half of the crop diseases are caused by fungal pathogens, which comprise the majority of crop pathogens. In addition to germplasm improvement via breeding and application of agrochemicals, another efficient strategy for disease prevention and control is to isolate and apply the biocontrol rhizospheric and/or endophytic microorganisms of the crop. [Objective] In this study we screened, isolated, and identified the endophytic bacteria with antagonistic effect against fungal pathogens infecting major crops from sugarcane to provide a theoretical basis for developing a new strategy for the biocontrol of crop fungal diseases. [Methods] Plate confrontation assay was used to isolate bacteria against multiple crop pathogenic fungi from sugarcane leaves. We identified the isolates based on 16S rRNA gene sequences, tested the inhibitory effect of the candidate strain on the sexual mating/filamentous growth and teliospore germination of Sporisorium scitamineum causing sugarcane smut, and then carried out field trial to explore the effect of the strain on sugarcane smut under field conditions. Furthermore, we examined the inhibitory effect of the candidate strain on the appressorium formation of Pyriculariaoryzae causing rice blast, as well as on diseased spot formation of detached leaves and rice seedlings cultivated in pots. [Results] The isolated bacterial strain CGB15 was identified as Bacillus amyloliquefaciens. CGB15 suppressed sexual mating/filamentous growth of S.scitamineum, making the fungal colony appear smooth under confrontation culture conditions. CGB15 suppressed the teliospore germination of S.scitamineum, with an inhibitory rate of (89.01±0.12)%. Under field conditions, CGB15 treatment showed a relative disease control rate of 48.65%. The supernatant of the fermented liquid of CGB15 inhibited the appressorium formation of P.oryzae, with an inhibitory rate of (93.55±1.11)%. Moreover, such supernatant suppressed the formation of diseased spots on detached leaves and rice seedlings cultivated in pots. We thus infer that CGB15 can produce and secret bioactive compounds to suppress the cell differentiation and pathogenicity of P.oryzae. [Conclusion] B.amyloliquefaciens CGB15 is an endophytic bacterial strain isolated from sugarcane leaves and has the potential to be applied in the prevention and control of sugarcane smut and rice blast.