Antifungal and plant growth promotion activity of volatile organic compounds produced by Bacillus amyloliquefaciens

Fusarium wilt of watermelon, caused by F. oxysporum f.sp. niveum (FON), is a devastating disease that causes extensive losses throughout the world. Five bacterial strains (L3, h, β, b, and L) isolated from the watermelon rhizosphere showed antagonistic activity against FON during in vitro tests. Strain L3 produced diffusible and volatile organic compounds (VOCs) which showed the strongest antifungal activity. Arabidopsis thaliana plantlets exposed to VOCs produced by strain L3 showed a 2.39‐fold increase in biomass, 1.40‐fold increase in primary root length, and 5.05‐fold increase in number of lateral roots. Confocal laser scanning microscope showed that the GFP‐labeled strain L3 could colonize along the elongation and differentiation zones of watermelon roots. In greenhouse pot experiments, the biocontrol efficiency of strain L3 against fusarium wilt of watermelon was up to 68.4% in comparison with the control treatment. In addition, inoculation of the strain L3 resulted in a 23.4% increase in plant fresh weight. Based on 16S rDNA sequence analysis, the strain L3 was identified as Bacillus amyloliquefaciens L3. Fourteen VOCs produced by strain L3 were identified through GC‐MS analysis. Of nine VOCs tested, 2‐nonanone and 2‐heptanone were proved to have strong antifungal properties. Acetoin and 2,3‐butanediol were found to promote plant growth. The results suggested B. amyloliquefaciens L3 was a potential biocontrol agent, and that VOCs produced by B. amyloliquefaciens L3 play important roles in the process of biocontrol and plant growth promotion. Arabidopsis thaliana plantlets exposed to volatile organic compounds produced by Bacillus amyloliquefaciens showed antagonistic activity against Fusarium wilt of watermelon: a 2.39‐fold increase in biomass, 1.40‐fold increase in primary root length, and 5.05‐fold increase in the number of lateral roots.