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The present study was conducted to determine the plant growth-promoting activities of Bradyrhizobium sp. (vigna) strain MRM6 grown in the presence and absence of the selected herbicides, quizalafop-p-ethyl and clodinafop. The herbicide tolerant Bradyrhizobium sp. (vigna) strain MRM6 was further tested for bioremediation and plant growth promoting potential using greengram as a test crop, grown in soils treated with quizalafop-p-ethyl and clodinafop, at both recommended and higher dose rates. The quizalafop-p-ethyl and clodinafop tolerant Bradyrhizobium sp. (vigna) strain MRM6 recovered from the nodules of greengram plants produced a substantial amount of indole acetic acid, siderophores, hydrogen cyanide and ammonia, both in the presence and absence of technical grade quizalafop-p-ethyl and clodinafop under in vitro conditions. Both quizalafop-p-ethyl [40 (recommended dose), 80, and 120 µg kg-1 soil] and clodinafop [400 (recommended dose), 800, and 1200 µg kg-1 soil] decreased the growth of Bradyrhizobium sp. MRM6-inoculated and un-inoculated plants. Quizalafop-p-ethyl at all concentrations showed more phytotoxicity and affected the growth in terms of nodulation, total dry biomass, nutrients (nitrogen and phosphorus) uptake and seed yield compared to clodinafop or un-inoculated control. When the inoculant strain MRM6 was used with any concentration of the two herbicides, the growth and nodulation parameters of the plants were relatively better compared to the plants grown in soils treated solely (without inoculant) with the same concentration of each herbicide. For example, when strain MRM6 was used with 1200 µg clodinafop kg-1 soil, it increased the symbiotic attributes (nodule number, nodule dry mass, leghaemoglobin), whole biomass, root N, shoot N, root P, shoot P, seed yield, and grain protein by 14%, 62%, 60%, 102%, 23%, 31%, 9%, 10%, 72% and 4%, respectively, compared to the un-inoculated treatment having the same concentration of clodinafop. The present findings suggest that the bradyrhizobial strain MRM6 endowed with multiple properties could be used to facilitate the productivity of greengram under herbicide-stressed soils.

Keywords: Bioremediation, Herbicide-stress, Legume, PGPR (Plant growth promoting rhizobacteria), Toxicity

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