Phylogenetic and characterization of salt-tolerant rhizobial strain nodulating faba bean plants

Abstract

Improvement of faba bean production in the new reclamation land in Egypt requires isolation and selection of effective abiotic stress tolerant rhizobial strains. Three rhizobial strains were isolated from healthy faba bean plants growing in different geographic areas in Egypt. These isolates were adapted against different concentrations of NaCl (100, 150 and 200 mM) by using the enrichment method. They were evaluated by measuring the symbiotic N2-fixation parameters under greenhouse and field conditions during two seasons (2010/2011 and 2011/2012). One rhizobial strain exhibited the highest values of symbiotic N2-parameters, nitrogenase activity and proline content. Based on 16S rDNA and nifH gene sequence, this strain was shown to belong to the Rhizobium leguminosarum bv. viciae. A strong similarity was found between the 16S rDNA and nifH gene sequence of the strain E15 and R. leguminosarum bv. viciae 3841 (100% similarity for 16S rDNA and 95% similarity fornifH gene). The results show that the maximum growth of this strain was obtained at pH 7 and 30°C. This strain was tolerant to drought stress till 20% polyethylene glycol and it yielded the highest concentrations of indole-3-acetic acid (IAA) at the end of the logarithmic phase. This strain solubilized inorganic phosphorus. R. leguminosarumbv. viciae was able to survive, persist, grow and effectively nodulated faba bean plants at high salt concentrations under greenhouse and field conditions and it could be used for biofertilization to reduce the severe effects of salinity and drought stress in the new reclamation land in Egypt. Key words: Vicia faba, Rhizobium leguminosarum bv. viciae, abiotic stress, nifHgene.