Potential for plant growth promotion of Kocuria arsenatis Strain ST19 on tomato under salt stress conditions

This study aims to assess the effect of five endophytic bacteria on the growth promotion of tomato plants under salt stress conditions. Twenty-five endophytic bacteria were isolated from roots of the native halophyte Stipa tenacissima L. collected from Djelfa (Algeria) and were evaluated for their halotolerant potential. Seven strong halotolerant isolates were selected and characterized for in vitro Plant Growth Promotion (PGP) including the ACC-deaminase activity, inorganic phosphate solubilization and the production of indole-3-acetic acid and siderophores. Five strains showing high PGP traits were investigated for the mitigation of salt stress and PGP of tomato (Solanum esculentum L. cv. Aïcha). Screening of the salt-tolerant isolates for PGP traits in saline condition (75 mM NaCl) under Petri-dishes experiment of tomato revealed that three isolates ST09, ST18 and ST19 improved the growth of tomato seedlings by highlighting germination rate, shoot and root lengths and biomass. Under greenhouse conditions at 0 and 75 mM NaCl, inoculation of strains ST09, ST18 and ST19 in tomato seedlings produced an increase in germination (69.23%, 73.07% and 73.07%). The isolate ST19 showed an increase of more than 90% in root elongation and 17.4% increase in biomass when compared to uninoculated tomato seedlings at 75 mM NaCl stress. Phylogenetic analysis based on the 16S rRNA gene showed that the strain ST19 belongs to the genus Kocuria, and is closely related to Kocuria arsenatis |CM1E1|KM874399T (99.29% similarity). Thus, we conclude that the inoculation of tomato plants with the strain ST19 showed its efficiency to mitigate salt stress conditions.