Salt tolerance of endophytic root bacteria and their effects on seed germination and viability on tomato plants

Salinity is one of the most brutal environmental factors limiting the productivity of agricultural lands worldwide. It is considered that the salinity may be one of the important reasons for the low yield in Iğdır of the tomato plants, which is medium resistant (3-5 dS.m^-1) among vegetables. Eco-friendly techniques such as endophytic root bacteria treatments (ERB) are needed to restore saline soils to agriculture and also to increase the yield of tomatoes. Endophytic bacteria colonizing the inside of plants increase plant growth by various mechanisms and also mitigate the adverse effects of biotic and abiotic stresses on plants. In this study, endophytic bacteria were isolated from the roots of tomato plants exposed to salt stress. Then, these isolates' tolerance levels to different NaCl (0, 0.1, 0.2, 0.4, 0.8 M) concentrations and their potential to promote plant growth (PGP) traits were determined. It was recorded that 14.8% of the isolates whose salt tolerance was tested were highly tolerant to NaCl and 18.5% were highly susceptible. The tested ERB isolates exhibited typical PGP characteristics such as siderophore production (4-30 mm diameter), phosphate solubilizing activity (6-16 mm diameter), and IAA production activity (24.9-171.6 µg/ml). Moreover, it was determined that the nitrogen fixation potential is high 55.7% of the isolates tested, and 11.1% low. In addition, the effects of ERB treatments on germination and vigor index in two tomato cultivars under standard and saline conditions in the lab were evaluated. Some ERB isolates in tomato plants under standard and saline conditions increased seed viability, hypocotyl length, root length, and seedling fresh weight, and also accelerated germination.