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Three experiments were conducted in order to investigate the effect of water deficiency on nodulation, rhizobial diversity and growth of common bean. In the first experiment, the effect of water deficiency was studied on two soil samples under glasshouse conditions. A significant decrease in nodulation and shoot dry weight production was observed. The molecular characterization of the root nodule isolates by PCR-RFLP of 16S rRNA and nodC genes showed that the nodulation by Rhizobium etli was severely inhibited. The in vitro analysis of salt tolerance indicated that drought stress favoured nodulation by salt-tolerant strains. In the second experiment, the effect of water deficiency was studied on sterilized sand using Rhizobium tropici CIAT899(T) and Ensifer meliloti bv. mediterranense 4H41 as inoculants. The results showed that strain 4H41, which is the more salt tolerant, was more competitive and more effective under water deficiency than strain CIAT899T. In the third experiment, the strain 4H41 was used to inoculate four fields. A significant increase in nodule number, shoot dry weight and grain yield was observed even in the non-irrigated soils. This work constitutes the first report of a strain enhancing the growth and the grain yield of common bean under water deficiency. (c) 2007 Elsevier Ltd. All rights reserved.