Evaluation of Two Bacterial Antagonists in Controlling Tomato Damping off Pathogen, Rhizoctonia solani under In Vitro and In Vivo Conditions

Abstract

The antagonism exerted by two bacterial strains, Burkholderia gladioli (F79) and an unidentified strain (C31) was tested against an isolate of Rhizoctonia solani, a major causal agent of damping off disease in tomato. In response to dual culturing with F79 and C31 on potato dextrose agar (PDA), Percent Inhibition of radial growth (P1RG) values exhibited a significant in vitro growth inhibition (P<0.05) of R. solani at 44% and 37% by F79 and C31, respectively after 4 days of culturing (DAC). Microscopic observations exhibited abnormal swellings and darkening of the mycelia subjected to antagonism, compared to the colorless thread-like mycelia in the control. To determine the effect of antagonists in controlling pre-emergence and post-emergence damping off in tomato in vivo, crushed sclerotia were first inoculated to seeds and two weeks old seedlings, by dipping in an aqueous suspension for two hours, followed by dipping in 108 cells/ml cell suspensions of either F79 or C31 antagonists for 30 min. The control was maintained without antagonists treatment. Five days1 after sowing on sterile moist filter papers, the seeds treated with F79 and C31 strains following R. solani sclerotia inoculation, showed 27% and 54% germination, respectively, compared to 13% germination in the control experiment (P<0.05). Of the treated seedlings that were transferred to sterile potting media in pots, 14% were healthy at 8 DAC in F79 treatment, compared to 6% recovery rate in the control experiment The results of this study revealed the potential of using F79 and C31 bacterial strains for the control of tomato damping off disease caused by R. solani. Further in vivo evaluations are required to ascertain their stability as potent bio control agents.