Meloidogyne incognita is a plant pathogen causing root-knot nematodes disease in many crops worldwide. Due to the environmental threat on the use of chemical fumigants, there is a need for a biological control method using microbial antagonists on root-knot nematodes disease. Therefore, this study was conducted to screen and evaluate the biocontrol potential of P. fluorescens strains against root-knot nematodes. The effectiveness of six P. fluorescens strains viz., Pf1, Pf2, Pf3, Pf4, Pf5and Pf6 were tested in vitro and also in pots experiment for their inhibitory activities and biocontrol potential against root-knot nematodes disease caused by Meloidogyne incognita on okra plant. Treatments of the nematode with 1.0-6.0% concentrations of 108 CFU/mL of Pf4 and Pf5 strains caused 70.0-95.0% inhibition on nematode egg-hatch and 2nd stage juveniles activity. Pf3, Pf4 and Pf5showed a decrease in the number of roots galling with increased root and shoot dry weights of stressed okra plant. Moreover, there was 25.99-36.43%, 37.76-79.145% and 42.62-62.37%, 69.83-98.09% increase in shoot length and leaf areas after 15th and 30th day respectively of P. fluorescens inoculation. The inoculated okra plants exhibited higher photosynthetic pigments, higher antioxidant enzymes activity and mineral contents than the nematode treated groups. Higher mineral contents were observed in the roots than the leaves of the okra plant subjected to the nematode infection. The bacteria strains especially Pf4 and Pf3 have considerable potential to reduce the menace of the nematodes in the treated okra plant. Therefore, the strains can be used for crop management against root-knot nematodes disease.
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