IMPROVED N-2 FIXATION IN 2,4-D TREATED WHEAT ROOTS ASSOCIATED WITH AZOSPIRILLUM-LIPOFERUM - STUDIES OF COLONIZATION USING REPORTER GENES

Among several Azospirillum strains tested for N-2 fixation in associat ion with wheat in a model system, 2 A. lipoferum strains (SpBr17 and 5 96) were found to be more efficient than the 8 other A. lipoferum and A. brasilense strains tested. Plants treated with low concentrations ( 0.7 mu g ml(-1)) of 2,4-dichlorophenoxyacetic acid (2,4-D) followed by inoculation supported larger acetylene reduction activity than plants treated only with bacteria. Three broad host range plasmids carrying lacZ, as a reporter gene, controlled by nifA, nodG and ntrC promoters were transferred to A. lipoferum SpBr17 and strain 596 by conjugation. All the transconjugants showed high beta-galactosidase activity in th e free-living condition. Studies on colonization of wheat roots using the SpBr17 nodC-lacZ gene fusion, which expressed the lacZ gene at the highest level, indicated the localization of bacteria on the young pa rts of roots as a thick coat. Counts of azospirilla on plant roots sho wed increased association of bacteria in 2,4-D treated plants.