Mutation to resistance for virus N-1 in the blue-green alga Nostoc muscorum.

The spontaneous and nitrosoguanidine induced N-1 virus resistant mutants of the blue-green alga Nostoc muscorum were isolated with the average mutation frequency of 3.55 X 10(-5) and 6.08 X 10(-4) respectively. Of the surviving colonies 8 per cent became virus sensitive,whereas out of the remaining 92 per cent 9.3 per cent showed lysogenic behaviour and 13.3 per cent showed poor or no nitrogen fixing ability. Mutation to virus-resistance was independent of the presence of the virus.Spontaneous host range mutants of virus were not found in repeated experiments.