Evaluation of Trichoderma spp., Pseudomonas fluorescence and Bacillus subtilis for biological control of Ralstonia wilt of tomato

Abstract

Background: Ralstonia solanacearum is the major bacterial disease in tomato, which invades the roots of diverse plant hosts and colonizes xylem vessels causing wilt, especially in tropical, subtropical and warm-temperate regions. R. solanacearum produces several toxins helping it to invade the plant’s natural defense mechanism. Native isolates of Trichoderma spp., Pseudomonas fluorescence and Bacillus subtilis can be used as biocontrol agents to control the bacterial wilt and combined application of these beneficial microbes can give better results. Methods: Bacterial wilt infection in the field was identified by field experts and the infected plant part was used to isolate Ralstonia solanacearum in CPG media and was positively identified. Subsequently, the efficacy of the biocontrol agents was tested and documented using agar well diffusion technique and digital microscopy. 2ml of the microbial concentrate (10 9 cfu/ml) was mixed in one liter of water and was applied in the plant root at the rate of 100 ml per plant as a treatment method. Results: It was observed that the isolated Trichoderma spp. AA2 and Pseudomonas fluorescence PFS were most potent in inhibiting the growth of R. solanacearum, showing ZOI 20.67 mm and 22.33 mm, respectively. Digital microscopy showed distinct inhibitory effect on the growth and survival of R. solanacearum. The results from the field data indicated that Trichoderma spp. and Pseudomonas fluorescence alone were able to prevent 92% and 96% of the infection and combination of both were more effective, preventing 97% of infection. Chemical control methods prevented 94% of infection. Conclusions: Results showed the bio-efficacy of the native isolates. The various level of antagonistic effect against R. solanacearum shown by all 13 isolates, including the results shown by native isolates in the field, manifested the promising potential of the biocontrol agents, like Trichoderma and Pseudomonas against controlling the bacterial wilt infection.