Enhancement of growth and salt tolerance in Brassica napus L. seedlings by halotolerant Rhizobium strains containing ACC-deaminase activity

A greenhouse experiment was conducted with four (ACC) deaminase-producing halotolerant Rhizobium strains, R29 (Sinorhizobium mellilote), R103 (Sinorhizobium mellilote), R281 (Rhizobium legominozaroum bv. phaseoli) and R307 (Rhizobium legominozaroum bv. phaseoli) and evaluated for their efficiency in improving canola plant growth under salt stress (with (50 mM NaCl + MgCl2) and control treatments), as factorial in randomized complete block design with three replications. Results revealed that with increasing salinity in compared to the negative control (0 mM salt), the overall reduction of growth of canola seedlings was around 21.3%. However, Rhizobium strains inoculation significantly increase the shoot/root elongation, shoot/root dry weight, stem diameter, leaf numbers, RWC up to 15.3/27.5, 24.86/53.1, 18.4, 18.05 and 8.4% respectively, compared to positive control (50 mM salt). Salt stress also caused 1.12-fold reduction in the root/shoot dry weight ratio compared to the absence of salt, while the salt tolerance index (ratio of biomass of salt stressed to non-stressed plant) was significantly increased (up to 1.26-fold) in inoculated plants compared to positive control. Furthermore, nutrient uptakes (N, P, K up to 56.14, 38.2 and 36.5%) under salt stress by canola was significantly (P < 0.01) increased. In summary, this study indicates that the use of ACC-deaminase producing halotolerant Rhizobium bacteria mitigates the salt stress effects.