Understanding the diversity of Phosphate Solubilizing Nitrogen fixing bacteria in rhizosphere and bulk soil of C3 legume plants Cajanus cajan and Trigonella foenum graecum

Abstract

Soil is the paramount factor in agriculture. The bacterial diversity and population dynamics in the rhizosphere of C3 and C4 plants vary as they show different photorespiration pattern. Microbial diversity would be different in bulk soil and rhizospheric soil. Microbial activity in root habitat is responsible for plant productivity. Plant growth promoting rhizobacteria (PGPR) which reside in root system and around the roots, play an important role in increasing soil fertility, eliminating pathogens and plant growth promotion for developing environment friendly agriculture. Hence, it will be very insightful to understand the diversity of P solubilizing nitrogen fixing bacteria in rhizosphere of C3 and C4 plants. In this study we screened the isolates which show phosphate solubilizing and nitrogen fixing ability simultaneously. During this study, we screened phosphate solubilizing bacteria on Pikovskaya agar plates from Cajanus cajan (Pigeon pea) and Trigonella foenum-graecum (Fenugreek) on the basis of phosphate solubilizing index (PSI). Total of 66 PSBs were found. All the isolates were nitrogen fixing bacteria. These isolates were further characterized biochemically by molecular biology based method i.e. ARDRA. Furthermore, all these isolates were screened for PGP properties like IAA, Siderophore, HCN production. On the basis of highest PSI, four isolates were selected for future studies. On the basis of biochemical and molecular characterization, it was found that best PSB may belong to Pseudomonas sp./ Serratia sp./ Mesorhizobium sp./ Proteus sp. Isolates FR12 and PFF11 showed highest release of phosphate 491.4 and 398.8 μg/ml respectively from tricalcium phosphate (TCP). Whereas, elevated levels of IAA production 243.65 and 112.00 μg/ml were seen in isolates FR12 and PF1. Moreover, % Siderophore units were 11.57 for FB4, 13.36 for FR12 and 19.46 for PFF11. All four isolates gave HCN test positive. Based on the results, we could say that these isolates have higher phosphate solubilizing ability along with other crucial PGP traits. Species richness and evenness in a particular soil sample were determined by diversity indices. Pot experiment of these four isolates was then carried out. Plants of Cajanus cajan and Trigonella foenum-graecum inoculated with inoculum of these four isolates showed increased productivity, faster growth, high yield compared to the control. Thus, obtaining the isolates which show both phosphate solubilizing and nitrogen fixing abilities can help us to isolate this PGPR for agronomic interest.