Evaluation of plant-growth-promoting activities of rhizobacterium Pseudomonas putida under herbicide stress

The aim of this study was to evaluate the effect of selected herbicides (quizalafop-p-ethyl, clodinafop, metribuzin and glyphosate) at one, two and three times the recommended field rates on the plant-growth-promoting (PGP) traits of Pseudomonas putida strain PS9 isolated from the mustard rhizosphere. P. putida strain PS9 was selected for its high herbicide-tolerance and its production of substantial amounts of indole acetic acid, siderophores (salicylic acid and 2,3 dihydroxy benzoic acid) and exo-polysaccharides. It also exhibits HCN and ammonia releasing ability. A progressive, herbicide-concentration-dependent, decline in PGP properties (except exo-polysaccharide production) of P. putida strain PS9 was observed when the strain was grown in the presence of increasing concentrations of each herbicide. Generally, among the selected herbicides, the maximum toxicity to PGP traits of P. putida strain PS9 was shown by quizalafop-p-ethyl at three times the recommended dose. This study concludes that herbicides should be screened before field application for their degree of toxicity to PGP traits of beneficial microorganisms.