Evaluation of Antagonistic Properties of Indigenous Biological Control Agents against Fusarium oxysporum, Causal Agent of Tomato Vascular Wilt in Burkina Faso

Abstract

This study aims to contribute to the improvement of plant health through the use of beneficial microorganisms, isolated from soil samples in Burkina Faso to control Fusarium oxysporum. The suspension dilution method was used for isolation from soil samples. King's B and LBA media were used to isolate bacteria of the Pseudomonas and Bacillus species, respectively. The antagonistic potential of the different colonies isolated   was evaluated using the co-culture method and in vivo in vegetation pots. Two tests were carried out in the greenhouse using a completely randomised block design.  Seedling treatment was carried out by immersing their roots in the bacterial solution beforehand. The results revealed the presence of bacteria with antagonistic properties. Identification of the bacteria based on sequencing of the 16S region of ribosomal DNA, revealed that they belonged to three genera composed of Bacillus (B. subtilis, B. amyloliquefasciens and B. thuringiensis), Pseudomonas (P. fluorescens) and Burkholderia (Burkholderia sp.). The strains exhibited antagonistic activity, significantly inhibiting the mycelial growth of F. oxysporum, F. duofalcatisporum and E. sorghinum, except L. theobromae. The results indicated that the soil treatments provided control of tomato vascular wilt. The rhizobacteria tested were more effective (with protection indices (PI) ranging from 87.1% to 96.1%) when applied a week before the pathogen in the soil than with seedling treatments where the pathogen and antagonists were applied at the same time (PI ranging from 54% to 77%). In addition, all bacteria promoted the growth of tomato plants irrespective of treatment. Finally, they are not only potential biocontrol agents against tomato vascular wilt, but also also contributed to seedling growth. These antagonistic bacteria could be proposed as microbial biopesticides for a biological control strategy against Fusarium wilt.