Rhizosphere associated bacteria as bio fertilisers in herbicide treated alfalfa (Medicago sativa)

Abstract

Purpose: The objective of the current study was to identify native bacterial strains with potential to mitigate the abiotic stress, caused by the topical application of the herbicide imazethapyr, as well as promoting growth of alfalfa (Medicago sativa). Methods: The initial investigation, involved the isolation of bacteria from the rhizosphere of field grown alfalfa, which were subsequently screened for their ability to fix nitrogen, synthesis auxin, solubilise phosphate and potassium, and the production of lipase, protease and cellulase enzymes, in addition to their tolerance to imazethapyr. Results: Among the selected isolates, Serratiarubidaea (A), Pseudomonasputida (B) and Serratia sp. (C) were found to have highest potential for these growth promoting traits. However, auxin production was only detected in S. rubidaea. In the second phase of the study, the effects of soil inoculation with bacterial species A, B and C and Sinorhizobium meliloti(R), on the growth and development of alfalfa were assessed in pot and field experiments. The results of these experiments, indicated that herbicide application decreased both crop yield and photosynthetic pigments. In most cases, the herbicide was shown to have less impact upon the growth of the inoculated plants compared to the control. However, increase of yield traits, photosynthetic pigments and microbial population only occurred in plants treated by AB, AR and ABR bacterial inoculations. Conclusions: Thus, alleviation of herbicide stress in conjunction with growth promotion has been achieved by using native rhizosphere-associated bacterial isolates. These findings open new avenues of research to develop potent biofertilizers, that are effective under herbicide stressed conditions.