Isolation, identification, and improving nematotoxicity of rhizobacterial strains against Meloidogyne incognita

Background and objectives Root-knot nematodes, Meloidogyne spp., have been reported to cause severe losses to field, horticultural, and medicinal plants throughout the world. Chemical nematicides are routinely applied for protection of the aforementioned crops. Residues of these toxic nematicides are carried to the final consumed products, which can be quite hazardous to human health on consumption. Biocontrol by using antagonistic organisms to inhibit the pathogens and reduce diseases is an ecofriendly management tool. This study was planned to isolate, identify, and improve or increase the activity of two isolated rhizobacterial strains known to have nematicidal properties − based on preliminary studies − using protoplast fusion technique and assessing the nematicidal potential of the fusants against root-knot nematode, Meloidogyne incognita J2. Materials and methods Certain rhizobacterial colonies isolated from the rhizosphere soil of cucumber and banana plants were identified by 16S rDNA to Pseudomonas aeruginosa (accession number LC187271) and Bacillus licheniformis (accession number LC187270). They were manipulated using protoplast fusion technique to improve their nematicidal potentials. The fused protoplasts generated and 10 fusant isolates were assessed against M. incognita J2. Results and conclusion All the tested fusants exhibited increase in their nematicidal activity than their parents against root-knot nematode, M. incognita J2, under laboratory conditions. The percentages of nematode mortality after 72 h of exposure were 85 and 86% by B. licheniformis and P. aeruginosa suspensions, respectively, whereas the percentages of mortality caused by fusants ranged between 91 and 99% as compared with control. The obtained results indicated that protoplast fusion technique is a successful tool to enhance the lethal effect of the isolated rhizobacteria strains against root-knot nematode. The genetically engineered bacteria can play a dual role under field conditions as a biocontrol agent against nematode and subsequently improve plant productivity.