1 Faculty of Biology, National University of Uzbekistan, 100174, Tashkent, Uzbekistan. 2 Institute of Environmental Biotechnology, Graz University of Technology, Graz, Austria. 3 Department of Food and Environmental Sciences, P.O.B. 56, Biocenter 1, Viikinkaari 9, FIN-00014, University of Helsinki, Finland. Chapter 7 Alleviation of Salt Stress in Cucumber and Tomato by Root Colonising Bacteria EGAMBERDIEVA D 1,3 , BERG G 2 , LINDSTRÖM K 3 , AND L.A. RÄSÄNEN 3 ABSTRACT Saline conditions are known to suppress the growth of crops. One possibility to circumvent this problem is to use root colonizing, salt tolerant bacterial inoculants, which can alleviate salt stress in plants. To evaluate the effect of different plant growth promoting rhizobacteria (PGPR) under salt stress conditions, the four strains Pseudomonas putida 1T1, Pseudomonas trivialis 3Re27, Pseudomonas extremorientalis TSAU20 and Stenotrophomonas rhizophila ep-17 were analysed on cucumber and tomato in pot experiments. Four salinity levels (2.5, 5.0, 7.5 and 10.0 dSm –1 ) were maintained in potting soil amended with NaCl. Results showed that PGPR inoculation, even at higher salinities (7.5 dSm –1 ), significantly increased dry weight of cucumber and tomato by on average 68% compared with non- inoculated plants. All bacterial strains were salt tolerant, growing well with 3% NaCl in the growth medium, and survived in the rhizosphere , the numbers of Cfu being equal at salinity levels 0 – 7.5, All strains produced IAA under salt conditions in vitro. Due to the our results we recommend using of PGPRs as a seed dressing in the greenhouse and fields in order to improve the growth of cucumber and tomato in farmlands with a high soil salinity. Key words: Root colonisation, PGPR, Salinity, Cucumber, Tomato.