The performance of salt tolerant mutant BGR CN-6M was better than BGR CN-7M and their wild parents and also reference strain, BGR AU-1 in acid soil. The inoculation of BGR CN-6M to blackgram in acid soil significantly increased the growth parameters such as plant height and dry matter production and yield parameters such as number of branches plant-1, number of pods plan-1, number of dusters plant-1, test weight and grain yield at all levels of N tested. The acid tolerant mutant rhizobial BGR CN-6M can be used as a potential biofertilizer for blackgram grown in salt soil of Cuddalore and Nagapattinam districts of Tamil Nadu under rainfed condition with moderate level of nitrogen i.e. 10 kg N ha-1 which is 50 % of recommended dose. The application of rhizobial biofertilizer helps inreducing the fertilizer by 50 % (10 kg N ha1) and the input cost by nearly 20 per cent. Besides the yield ofblackgram significantly improved in salt soil.
