Response to salinity stress of Rhizobium leguminosarum bv. viciae strains and their host plants.

We investigated the effect of residual salts from the previous summer’s irrigation on two non-irrigated cover crops—broad bean and common vetch—and on their rhizobial symbiontics. Before sowing, seeds were inoculated with a salt-tolerant strain and a salt-sensitive strain of Rhizobium leguminosarum biovar viciae. An increase in the electrical conductivity of the saturated-soil extract from 2.0 dS m−1 to 6.0 dS m−1 caused a severe reduction of broad bean biomass, while growth of common vetch was almost unaffected by the salinity level. Our results clearly indicate that common vetch as a cover crop may increase the availability of nitrogen in soil more than broad bean also in saline environments. A high ability of both inoculated strains to nodulate Vicia plants was observed under controlled conditions. In contrast, inoculated strains were not able to nodulate plants in salinized soils, showing lower competitiveness compared to natural rhizobial population. Indeed, the new isolates from nodules were salt-sensitive when tested in vitro. The complex interaction among bacteria, plant and soil determined the survival of endogenous salt sensitive rhizobial strains and limited the success of inoculation with exogenous salt resistant rhizobia.