Isolation and characterization of a multiple herbicide resistant strain [Av(MHR)

The present study was aimed to isolate a multiple herbicide resistant strain [(MHR)] of Anabaena variabilis exhibiting resistance against four common rice-field herbicides, viz., Arozin, Alachlor, Butachlor and 2,4-D. The multiple herbicide resistant (MHR) strain was isolated by spontaneous mutational techniques. Of the four spontaneously occurring mutants, Arozin resistant mutant (Ar-R) exhibited 92-98% survival in lethal concentrations of Arozin, Alachlor, Butachlor and 2,4-D, and was designated as MHR strain, Av(MHR). The MHR strain exhibited faster growth rate, substantial increase in macromolecular contents, photosynthesis, nitrogenase and glutamine synthetase (GS) activity not only in graded concentration of herbicides but below (0-25 mg L) and above the lethal dosages (25-80 mg L), and even in the presence of combined lethal dosages of all four herbicides as compared to wild type as well as Alachlor, Butachlor and 2,4-D resistant strains. The cross resistance relationship in Arozin resistant (Ar-R) mutant strain of A. variabilis with lethal dosages of Alachlor, Butachlor and 2,4-D did indicate that it was a single mutational event and resistance to Arozin was associated with the acquisition of resistance to Alachlor, Butachlor and 2,4-D. Evidently such improved Av(MHR) strain of diazotrophic cyanobacterium A. variabilis under herbicide(s) stressed agro-ecosystem, particularly rice-fields, would likely to serve as efficient biofertilizer.