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 degrees C) and high (40 degrees C) temperatures. Sixteen strains showed important IAA production (50-123 mu g IAA/ml) and 11 were identified as high phosphate solubilizers (greater than 20 mu g/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.

Automated summary

This study tested the plant growth-promoting activities and phenotypic traits of 29 different Rhizobium laguerreae strains from Morocco. The results showed that some strains produced significant amounts of indole-3-acetic acid (IAA) and had high phosphate solubilization abilities. In pot and greenhouse experiments, the combination of selected R. laguerreae strains with two PGP bacteria strains resulted in increased plant biomass and nodule formation. These strains could be used to mitigate the effects of drought stress on lentil cultivation.