Understanding rice growth-promoting potential of Enterobacter spp. isolated from long-term organic farming soil in India through a supervised learning approach

This study addresses the plant beneficial enterobacteria present in rice rhizosphere and their efficiency for enhancing nitrogen uptake in rice plant. Using culturable approaches, the population of total diazotrophs present in rhizosphere samples collected from different organic rice fields of Sikkim were studied and recorded in the range between 4.62 to 4.97 log(10) CFU/g soil. All the isolated commonly occurred diazotrophic bacterial isolates were screened based on their ability to fix nitrogen in milligram per gram of sugar consumed under in-vitro condition with the reference check. In addition to nitrogen fixation, plant growth promoting traits such as production of indole-3-acetic acid and gibberellic acid were estimated using spectrophotometric approaches and compared against Bacillus subtilis as reference multi-potent plant growth promoting strain. In-vivo evaluation of these diazotrophic species in rice found improvement in both above and below ground responses in rice plant evaluated by estimating changes in chlorophyll concentration, plant biomass, root architecture, nitrogen uptake, microbial biomass and associated biochemical activity of soil. Further, the selected isolates were identified through DNA targeted analysis of 16S rRNA gene present in diazotrophs and which identified that the isolates belonged to the Enterobacter genus. Statistical models were prepared for deciphering the dynamics of plant growth improvement due to selective enrichment of rhizosphere bacteria and found significant (p<0.05) correlation between soil and plant parameters. This study concludes that Enterobacter spp. present in organic paddy soils of Sikkim having good nitrogen fixing abilities and whose selective enrichment in rhizosphere improved nitrogen uptake and plant growth promotion in rice plant.