Beneficial effect of Rhizobium laguerreae co-inoculated with native Bacillus sp. and Enterobacter aerogenes on lentil growth under drought stress

A collection of 29 Rhizobium laguerreae strains phylogenetically different originating from 4 biogeographic regions of Morocco were tested for their PGP activities and phenotypic traits. The strains showed different levels of tolerance to salt ranging from 0.5 to 1.5% NaCl, an optimal growth in neutral pH (7) and were sensitive to low (10 °C) and high (40 °C) temperatures. Sixteen strains showed important IAA production (50–123 μg IAA/ml) and 11 were identified as high phosphate solubilizers (greater than 20 μg/ml). A pot experiment enabled the selection of 3 R. laguerreae strains LMR575, LMR597, and LMR655 with a symbiotic efficiency of 78, 78 and 76% respectively. In a subsequent greenhouse experiment, the elite rhizobial strains were tested in single and combined inoculations with 2 PGP strains Bacillus sp. LMR698 and Enterobacter aerogenes LMR696 previously isolated from lentil rhizosphere using field soil. All treatments underwent two irrigation levels (30 and 50% of water retention capacity). Under sufficient watering conditions (50%), the combination of R. laguerreae LMR655 with both bacterial strains (E. aerogenes LMR696 and Bacillus sp. LMR698 increased plants biomass by 38 and 23% respectively and number of nodules (54 and 52 nodules/plant respectively). Whereas, under drought stress conditions (30%), all combination except R. laguerreae LMR575+ Bacillus sp. LMR698 yielded a shoot dry weight significantly comparable to nitrogen-fertilized control. Moreover, R. laguerreae LMR597 and LMR655 combined with E. aerogenes showed an increase of areal biomass of 8 and 3% respectively. These performing strains could be further exploited in agricultural practices to mitigate the drought stress effects for a sustainable lentil cultivation.