Novel halotolerant rhizobacterial strains mitigated the salt stress in-vitro and in-vivo and improved the growth of tomato plants

Abstract

Increasing land salinization has become one of the most damaging threats to the global modern agriculture and has challenged food production and food security. Plant growth promoting rhizobacteria (PGPR) have emerged as efficient biological tools to improve plant growth in stressed environments. The present study was conducted to isolate, identify and characterize halotolerant PGPR from an unexplored saline area of Pakistan. The effect of the isolated strains was evaluated in-vitro and on the tomato varieties grown under 150 mM salt stress in the field. A total of 12 strains were isolated and further screened in-vitro to check their halotolerance. The isolates were screened using nutrient agar medium supplemented with different levels (5, 10, 15, 20 and 25%) of NaCl. After screening, two highly salt tolerant strains were selected and identified using 16S rRNA technique. Isolates B9 and B10 were successfully identified as Pseudarthrobacter oxydans (NR_026236.1) and Staphylococcus pasteuri (NR_024669.1). The isolates were tested qualitatively for their biochemical and plant growth promoting traits. These isolates promoted tomato growth under salinity stress when applied alone or in consortium. The isolates demonstrated catalase and protease activity, phosphorous solubilization (PSI: 2.45, 2.63) and produced indole acetic acid. The current findings established that the isolated strains were highly resistant and tolerant up to 25% NaCl stress as compared to the other reported strains. These halophiles possessed promising plant growth promoting traits hence, are assumed to have great potential to serve as bioinoculants for the alleviation of adverse effects of salinity on crops.