Exploring wild Rhizobium isolates for development of Rhizobium mutants suitable for blackgram under acid soil condition

Abstract

Soil acidity is the major soil environmental stress factor limits Rhizobium survival and thereby reducing nodulation. In addition which results in deficiencies of Calcium, Magnesium, Potassium, Molybdenum and also cause aluminium toxicity which also affects nodulation and inturn the productivity in pulses. Developing a mutant strain of Rhizobium to tolerate acidity from wild type available in the acid soils will survive in soil and enhance the nodulation thereby improve N2 fixation. In the present study the three Rhizobium mutants viz,. VM1, VM2 and VM3 were developed using EMS mutagen for Chloramphenicol resistance from the native Rhizobium strains isolated from blackgram nodules grown under acid soils (pH 4.5 to 5.0) of NPRC, Vamban. Among the three, VM1 alone tolerated 200 ppm Chloramphenicol and others showed meagre growth. In the acid tolerant test VM1 Rhizobium mutant alone grew at both acidic pH levels (5.0 & 4.0) and confirmed in BOX PCR analysis also. The Rhizobium mutant (VM1) increased the ability of wild mutant to grow on acidic pH without causing major alteration in its DNA.