Aim:  To study the effect of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) deaminase from Pseudomonas fluorescens against saline stress under in vitro and field conditions in groundnut (Arachis hypogea) plants. Methods and Results:  Four plant growth‐promoting rhizobacteria (PGPR) strains were used in this study to evaluate their efficacy in groundnut plants against saline stress under in vitro. Among the four PGPR strains used, Ps. fluorescens strain TDK1 showed greater performance in improving the plant growth parameters of groundnut seedlings in vitro. PCR amplification using Pseudomonas‐specific 16S‐23S rRNA internal transcribed spacers (ITS) primers revealed that all the four strains belonged to the group of fluorescent pseudomonads. ITS region of Ps. fluorescens strain TDK1 was cloned and sequenced. ACC deaminase activity using biochemical and molecular (PCR) analysis revealed that among all the four strains, Ps. fluorescens strain TDK1 showed greater amount of ACC deaminase activity and positive reaction to PCR amplification. ACC deaminase gene from Ps. fluorescens strain TDK1 was isolated, cloned and sequenced. Pseudomonas bioformulations were developed and they were tested in groundnut plants under saline‐affected soils. The results indicated the superior performance by Ps. fluorescens strain TDK1 possessing ACC deaminase activity in improving yield parameters in groundnut plants despite salinity. Conclusions:  Pseudomonas fluorescens strain TDK1 possessing ACC deaminase activity enhanced the saline resistance in groundnut plants, which in turn resulted in increased yield when compared with the groundnuts treated with Pseudomonas strains not having ACC deaminase activity. Significance and Impact of the Study:  The promising role of ACC deaminase from Ps. fluorescens strain TDK1 in alleviating saline stress has been concluded in groundnut plants. This study will be useful for exploiting the activity of ACC deaminase from microbial strains against various biotic and abiotic stresses wherever ACC accumulated as precursor for ethylene biosynthesis.

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Plant growth promoting bacterial (PGPB) strains Pseudomonas fluorescens Pf1 and endophytic Bacillus subtilis EPB5, EPB22, EPB 31 were tested for their capacity to induce water stress related proteins and enzymes in green gram (Vigna radiata) plants. Among the different bacteria used, P. fluorescens Pf1 increased the vigour index, fresh weight and dry weight of green gram seedlings in vitro. Quantitative and qualitative analyses of stress-related enzymes indicated the greater activity of catalase and peroxidase in green gram plants bacterized with P. fluorescens Pf1 against water stress when compared to untreated plants. The greater accumulation of proline was recorded in Pf1 treated plants compared to untreated plants. The pot culture study revealed the greater resistance to water stress by green gram plants treated with P. fluorescens Pf1 compared to untreated plants. The greater activity of stress-related enzymes in green gram plants mediated by PGPB could pave the way for developing drought management strategies.

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