Diverse culturable diazotrophic endophytic bacteria from Poaceae plants show cross-colonization and plant growth promotion in wheat

Diazotrophic endophytic bacteria colonizing cereal plants have a tremendous scope to increase crop yields by supporting low input sustainable agricultural demands of nitrogen. Present work was aimed at studying diversity and functional attributes of nitrogen fixing bacterial endophytes from cereal plants. Diazotrophic endophytic bacteria from cereal plants were enriched on nitrogen-free medium and their diversity analyzed by PCR-denaturing gradient gel electrophoresis. Evaluation of plant growth promoting traits of individual isolates and their effect on wheat plants was carried out in plant-soil system. DGGE analysis and band sequencing showed diazotrophic community to be similar in different plant parts but different than total endophytes. Thirty-one nitrogen fixing endophytic bacteria affiliated to Actinobacteria, Proteobacteria and Firmicutes representing 14 genera were isolated, where Arthrobacter, Rhizobium, and Bacillus spp. were more cosmopolitan. Cross-colonization of the endophytes monitored by green fluorescent protein tagging showed that they are not plant specific. All the bacterial isolates showed presence of nifH gene, siderophore production whereas 81% and 48% isolates showed IAA and P-solubilization, respectively. Biocontrol activity was seen only in Streptomyces spp. which inhibited the growth of Rhizoctonia solani. Pot experiments conducted with wheat plant inoculations showed good growth promotion and correlated with IAA and siderophore production by the isolates. Diverse endophytic nitrogen fixing bacteria colonize cereal plants non-specifically and possess other plant beneficial traits which help in plant growth promotion.