Toxicity Assessment of Herbicides Quizalafop-p-Ethyl and Clodinafop Towards Rhizobium Pea Symbiosis

In modern conventional agriculture, herbicides are frequently used to prevent yield losses due to weeds. Herbicides also affect negatively the productivity of legumes. With these considerations, we evaluated the effects of soil applications of different concentrations of quizalafop-p-ethyl and clodinafop on the performance of Rhizobium inoculated pea, grown in clay pots. In this study, the concentration of herbicides higher than the recommended rates of quizalafop-p-ethyl and clodinafop adversely affected the dry matter accumulation, symbiotic properties, grain yield and nutrient status of pea plants. Toxicity of quizalafop-p-ethyl and clodinafop to pea plants increased progressively with increase in rates of herbicides. Of the two herbicides, quizalafop-p-ethyl was more toxic than clodinafop. In contrast, when herbicide tolerant Rhizobium strain MRP1 was also used with herbicide, it increased the measured parameters at all concentrations. A maximum increase of 11%, 17%, 46%, 33%, 21% and 7% in the root N, shoot N, root P, shoot P, seed yield and seed protein, respectively, was observed when MRP1 was used with 120 mu g quizalafop-p-ethyl kg(-1) soil while with 1,200 mu g clodinafop kg(-1) soil it increased the root N, shoot N, root P, shoot P, seed yield and seed protein by 20%, 9%, 56%, 56%, 29% and 7%, respectively, compared with the un-inoculated but herbicide treated control. This study suggested that the toxic effects of herbicides on pea plants could be attenuated by applying growth promoting herbicide tolerant strain of Rhizobium under herbicide stressed soil environment.