Annals of Plant Protection Sciences

In this study, a total of 70 bacterial isolates belonging to genera Bacillus and Pseudomonas were isolated from rhizospheric soils of mustard. Plant growth promoting traits, like solubilization of inorganic phosphate (P) and production of indole acetic acid (IAA), ammonia (NH₃), hydrogen cyanide (HCN), siderophores and catalase was assessed both in the presence and absence of technical grade of herbicides (quizalafop-p-ethyl & clodinafop). A total of 18 isolates showed the plant growth promoting activities both in the presence and absence of the tested herbicides. On the basis of multiple plant growth promoting activities, bacterial isolates were further evaluated for their tolerance to the selected herbicides. Among these, Bacillus strains PS 2, PS 9 and PS 19 and Pseudomonas strain PS 1 showed maximum tolerance to quizalafop-p-ethyl (1200 to 1600 μg mL⁻¹) and clodinafop (1600 μg mL⁻¹), quizalafop-p-ethyl (at 40 & 80 μg L⁻¹) and clodinafop (at 400 & 800 μg L⁻¹) reduced P solubilization, synthesis of IAA and siderophores. Among the two herbicides, quizalafop-p-ethyl was more toxic than clodinafop. Hydrogen cyanide and ammonia production by the isolates however, did not change following any concentration of two herbicides. This study suggested that the metabolic activities of plant growth promoting rhizobacteria (PGPR) decline following herbicides application.