Isolation and Characterization of Antagonistic Bacterial Strains for Biocontrol of Collar Rot (Aspergillus niger) in Groundnut (Arachis hypogaea L.)

Aspergillus niger is a pathogenic fungus causing collar rot disease in groundnut (Arachis hypogaea L.). The species is currently recognized as one of the most severe threats to groundnut worldwide, negatively impacting on productivity and quality of groundnut. This study was conducted to isolate bacterial strains capable of inhibiting the pathogenic A. niger QT1 strain as well as the production of some extracellular cell wall hydrolytic enzymes. A preliminary screening resulted in a total of 138 bacterial isolates exhibiting endo-β-1,3-glucanase activity. The second screening resulted in 10 isolates showing strong antagonistic activities against A. niger QT1 of 41.05 to 61.6% inhibitory ability. Among these, five isolates produced high cell wall hydrolytic enzymes, including endo β-1,3-glucanase, chitinase, and cellulase. Using the nucleotide sequence of 16s rRNA as a marker, it was revealed that these isolates were identified as Bacillus velezensis (2 strains), and Bacillus siamensis (3 strains). The in vivo evaluation of the potential application for treatment of A. niger QT1 demonstrated that all five strains effectively controlled collar rot disease of groundnuts. The highest efficacy was observerd in the treatment supplemented with B. velezensis 137 with no groundnut death. The present results strongly supported for the application of bacteria as biocontrol agents in order to replace the use of chemical plant fungal pesticides.