MANGANESE-RESISTANT MUTANTS OF AZOSPIRILLUM BRASILENSE: THEIR GROWTH AND RELATIVE EFFICIENCY IN ASSOCIATIVE NITROGEN FIXATION WITH CHEENA (PANICUM MILIACEUM) IN ACID SOIL

Abstract

Nitrosoguanidine-induced manganese-resistant mutants Mn^r101, Mn^r107, Mn^r105, Mn^r193, Mn^r2-15 and Mn^r2-7 of Azospirillum brasilense were isolated and used for associative nitrogen fixation with cheena (Panicum miliaceum L.) genotype RArM6 in acid soil (pH 5.3). Three of the Mn-resistant mutants (Mn^r105, Mn^r193 and Mn^r101) showed crossresistance to aluminium (2.5ppm) and neomycin (15-50μg/ml) but not to streptomycin except Mn^r101 and Mn^r107. It is also suggested that these three mutants may be most suitable for nitrogen economy in acid soils having various pH and associated factors of acidity.