Combining biocontrol agents, Saccharomyces cerevisiae and Bacillus subtilis against root rot disease caused by the pathogenic fungus, Fusarium solani

Abstract

Local isolates of Saccharomyces cerevisiae and Bacillus subtilis had an antagonistic potential against Fusarium solani, the causes of root rot disease in pepper plants. Maximum antagonism was obtained when the mixture of the two biocontrol agents were used. Image Analysis System revealed interaction between Saccharomyces cerevisiae and / or Bacillus subtilis and the phytopathogen (Fusarium solani) led to fungal mycelium deformation and coiled spiral, zigzag or fragmented hyphae of the pathogen appeared. Application of the two biocontrol agents reduced disease percentage of pepper plants reaching 15% when the seeds of pepper plants were treated with the mixture of S. cerevisiae and Bacillus subtilis, 25% and 30% when S. cerevisiae and Bacillus subtilis were used respectively, compared with control 75% (F. solani). Also, improved seedling lengths and fresh and dry weights of plants were obtained as a result of Saccharomyces cerevisiae and / or Bacillus subtilis application. Data also revealed that, when F. solani co-cultured with S. cerevisiae and / or Bacillus subtilis, total soluble protein, peroxidase and polyphenol oxidase enzymes were increased in the cultures. The two biocontrol agents also revealed extracellular chitinolytic activity in the presence of the phytopathogen as evaluated by chitin mineral agar plate assay. The results showed that under anaerobic conditions, Bacillus subtilis exhibited increased antagonism toward Fusarium solani, when nitrate was present in the growth medium. Addition of 2.5 and 5 mM potassium nitrate, however exhibited a more pronounced effect on the reduction of the fungal colony diameter than 10 and 100 mM concentrations