Bacillus amyloliquefaciens: a versatile antimicrobial Firmicute for the suppression of wilt caused by Ralstonia pseudosolanacearum in tomato

ABSTRACT

Rhizosphere bacteria based biological control strategy is an eco-friendly approach to protect crops from various plant diseases. Among these, spore-forming Bacillus, abundant in the rhizosphere, provide unique advantages for plant health. This study focused on characterising two tomato rhizosphere-associated Bacillus amyloliquefaciens strains (Trb7 and Trb11), highly effective against the bacterial wilt pathogen Ralstonia pseudosolanacearum in vitro. Species identification was based on partial 16S rRNA gene sequencing, supported by phylogenetic analysis. Five antimicrobial peptide (AMP) genes (surfactin, fengycin, bacilysin, subtilin, and spore protein) were detected in both the isolates of B. amyloliquefqciens using specific molecular markers. Greenhouse trials showed that prophylactic application of these isolates led to an 83.4% reduction in tomato bacterial wilt, with only 16.6% wilt incidence compared to the 100% in the R. pseudosolanacearum-inoculated control. Moreover, these B. amyloliquefaciens isolates exhibited plant-growth-promoting traits in vitro. Interestingly, they also showed significant inhibition of mycelial growth against Sclerotium rolfsii and Alternaria alternata, major fungal pathogens in tomatoes. Overall, our findings highlight the potent bactericidal role of B. amyloliquefaciens isolates in suppressing R. pseudosolanacearum in tomatoes.

Key highlights

1. Two among the 100 Bacillus displayed antibacterial activity against Ralstonia pseudosolanacearum.

2. Antibacterial firmicutes was identified as Bacillus amyloliquefaciens through the 16S rRNA gene sequence analysis.

3. Five AMP genes (srfAA, fenD, bacA, spas, and spoVG) were identified in the isolates.

4. Delivery of B. amyloliquefaciens drenching on rhizosphere significantly reduced wilt.

5. Additionally, B. amyloliquefaciens showed the antifungal activity on Sclerotium rolfsii and Alternaria alternata.

GRAPHICAL ABSTRACT

Graphical abstract depicting the isolation and characterisation of Bacillus amyloliquefaciens for the suppression of wilt caused by Ralstonia pseudosolanacearum in tomato. Figures was created and manually edited in Biorender.com.

KEYWORDS:

• Rhizosphere Bacillus
• bacterial wilt
• antibacterial
• AMP gene
• PGPR
• antifungal

Acknowledgements

We thank to University Grants Commission (UGC) for providing financial assistance to carry out this study. Various facilities provided by the Head, Department of Plant Pathology, Tamil Nadu Agricultural University, Coimbatore, are gratefully acknowledged. The authors are thankful to Director, ICAR-IARI, for providing the necessary facilities to complete this work successfully. Dr. Aundy Kumar is grateful to CRP (Genomics) for providing funds for supporting the work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Compliance with ethical standards

Our manuscript ‘Bacillus amyloliquefaciens: a versatile antimicrobial Firmicute for the suppression of wilt caused by Ralstonia pseudosolanacearum in tomato’ complies with the Ethical Rules applicable to the Biocontrol Science and Technology journal.

Additional information

Funding

This work was supported by University Grants Commission [Fellowship ID - F1-17.1/2014-15/RGNF-2014-15-SC-TAM-86150]; CRP Genomics [CRP-Genomic/VIII/2020-22].