SYMBIOTIC EFFICIENCY OF AZIDE RESISTANT MUTANTS OF PROSOPIS-CINERARIARHIZOBIA

Seven rhizobial mutants, with enhanced resistance to sodium azide (25 mu g ml(-1)), have been isolated following ultraviolet-irradiation of the native rhizobial strain, PC-1 (azide resistance 5 mu g ml(-1)), of Prosopis cineraria. Five out of the seven isolated mutants (azi-1, az i-2, azi-4, azi-6, azi-7) showed significant increases in per cent sho ot nitrogen (33-45%) and plant dry weight (14-40%) over the parent str ain, PC-1. However, two isolated mutants, azi-3 and azi-5, did not sho w any improvement in nitrogen-fixing efficiency, in terms of per cent shoot N and plant dry weight possibly due to high reversion frequencie s. It can be inferred that increased rhizobial resistance to azide and effectiveness are associated with each other in legume-Rhizobium symb iosis system.