Antagonistic activity and identification of antagonistic bacteria JB7 against Fusarium head blight

Abstract:

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the major diseases limiting wheat production. Biocontrol has been considered an effective and sustainable method for the control of crop diseases. [Objective] To screen out endophytic strains with inhibitory effects on F. graminearum from wheat grains and evaluate their biocontrol potential, providing strain resources and theoretical support for the development and utilization of biocontrol agents against FHB in wheat. [Methods] Plate confrontation, spore germination, and cell-free supernatant (CFS) inhibition experiments were carried out to screen out the endophytic strains with antagonistic activity against F. graminearum from wheat grains. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were employed to observe the conidial morphology, membrane integrity, and mycelial reactive oxygen species of F. graminearum treated with the CFS. Pot experiments were performed to verify the biocontrol effects of the endophytic bacteria on FHB. Illumina HiSeq was used for whole genome sequencing. [Results] A highly efficient endophytic strain JB7 inhibiting the growth of F. graminearum was isolated from wheat grains. The CFS of strain JB7 in the decline stage showed the inhibition rate of 85.23% on the spore germination of F. graminearum. Moreover, it led to concavity on spore surface, cell membrane damage, leakage of nucleic acids and proteins, and accumulation of reactive oxygen species in the mycelia of F. graminearum. The CFS of strain JB7 significantly increased the content of soluble protein and malondialdehyde. Strain JB7 could produce protease, cellulase, glucanase, and siderophores. Pot experiments showed that strain JB7 decreased the disease index of FHB (P<0.05) in wheat. The strain was identified as Bacillus methylotrophic JB7 by whole genome sequencing, and it carried 12 gene clusters for the synthesis of secondary metabolites with antimicrobial functions. [Conclusion] Strain JB7 could inhibit the growth of F. graminearum and demonstrated a strong control effect on FHB, serving as a candidate strain for the biocontrol of FHB in wheat.