Acid and salt tolerance behavior of Rhizobium isolates and their effect on microbial diversity in the rhizosphere of redgram (Cajanus cajan L.)

Abstract

Experiments were conducted in two phases, first under in vitro condition to study the stress tolerant ability and then in pot experiment to study the effect of Rhizobium isolates on rhizospheric microbial activity. The strain CHRS-7 could tolerate the pH 4.0, whereas RAN-1 and RAB-1 could not. The growth of all the strains was luxuriant in 1% NaCl solution and decreased with increase in the concentration of NaCl. All the strains could produce the phytohormone indole acetic acid (IAA) by metabolizing different carbon sources. The highest amount of IAA was produced by RAB-1 (81 µg/mL), CHRS-7 (78 µg/mL) and RAN-1 (72 µg/mL) by metabolizing mannitol, glucose , and sucrose, respectively. The higher bacteria and rhizobial population was enumerated in the treatment with inoculation of Rhizobium strains and added with 50% of soil test dose of nitrogen whereas higher fungi population was enumerated with the treatment receiving 150% of a soil test dose of nitrogen. The soil enzymes activity, microbial biomass carbon and nitrogen were also higher with a lower dose of external sources of N (50% of a soil test dose) and decreased with increase in nitrogen dose.