Pseudomonas sp.: A promising biocontrol agent against selected phytopathogens

Abstract

The biological control of plant pathogenic microorganisms by Pseudomonas sp. is attracting increasing attention in the agricultural world, since the indiscriminate use of toxic chemicals constitutes a potential threat to both human and animal health, as well as the environment. A total of 27 bacterial strains were isolated from the rizhospheric soil of the tomato (Solanum lycopersicum) plant, and their antagonistic activities against a few of the selected pathogenic bacteria and fungi were evaluated using dual-culture assays, biochemical tests for the production of Hydrogen Cyanide (HCN), Indole Acetic Acid (IAA), Iron Chelating Agent (siderophore), and phosphate solubilisation. Furthermore, the separated antagonists were examined for the generation of hydrolytic enzymes such as protease, amylase, ß-1, 3 glucanase, cellulose, chitinase, and pectinase. In all 27 strains isolated, the highest antagonistic activity was shown by only two bacterial strains Pseudomonas (VK1and VK2), against Klebsiella pneumoniae, Salmonella typhi, Xanthomonas campestris, Bacillus sp., Alternaria alternata, Aspergillus niger, A. flavus and Fusarium sp. Both the strains were identified as Pseudomonas sp. on the basis of morphological, physiological and biochemical characterization. Comparatively, strain VK1 was more effective against above pathogens than VK2 strain which was confirmed by dual culture assay. Both the strains of Pseudomonas sp. further were characterized for their antagonistic traits like production of HCN, IAA, siderophore, insoluble phosphate solubilising ability and hydrolytic enzymes properties. Similarly, VK1 strain showed positive test for all above biochemical tests, while VK2 strain was not able to produce IAA and showed negative test for phosphate solubilizing activities. So, VK1 strain of Pseudomonas was able to produce all above hydrolytic enzymes and found to be efficient antagonistic PGPRs. These findings indicated that isolated Pseudomonas sp. has a promising natural, eco-friendly, bio-safe and cost effective approach to cope against both phytopathogenic bacteria and fungi.