Effects of Bacillus cereus F-6 on Promoting Vanilla (Vanilla planifolia Andrews.) Plant Growth and Controlling Stem and Root Rot Disease
A lipopeptide-producing bacterium, Bacillus cereus (F-6), was isolated from the rhizosphere soil of a healthy vanilla (Vanilla planifolia) plant cultivated on a plantation under 21 years of continuous cropping with vanilla. A pot experiment was conducted to investigate the effects of the green fluorescent protein-tagged F-6 (F-6-gfp) and its bio-organic fertilizer (BIO) on vanilla plant growth and stem and root rot disease, using the same plantation soil. The application of BIO significantly increased the vanilla plant root, stem and leave dry weights; however, there was not a significant difference between the F-6-gfp-inoculated treatment and the control. Meanwhile, the BIO application also significantly reduced the severity of stem and root rot disease compared to the control. The rhizosphere soil population of Fusarium was approximately 10-fold smaller in the BIO treatment compared to the control treatment at 150 days after transplantation. The number of B. cereus F-6-gfp in the rhizosphere soil of the BIO treatment remained significantly higher than that of the F-6-gfp-inoculated treatment throughout the experiment. In conclusion, F-6-gfp successfully colonized the rhizosphere soil in the BIO treatment, promoting vanilla plant growth, reducing the disease severity index, and decreasing the Fusarium population number, helping to remove barriers to the continuous cropping of vanilla.