Rhizobacteria Capable of Producing ACC-deaminase May Mitigate Salt Stress in Wheat

Rhizobacteria may promote plant growth by cleaving plant-produced 1-aminocyclopropane-1-carboxylic acid (ACC) through ACC-deaminase activity. The effectiveness of plant-growth-promoting rhizobacteria (PGPR) for improving the growth and yield of wheat (Triticum aestivium L.) was evaluated under salinity stress. The effect of high ethylene concentrations on plant growth and performance of these strains for reducing this negative impact was also evaluated by conducting a classical triple-response bio-assay. Eighteen rhizobacterial strains containing ACC-deaminase were screened by conducting ajar experiment under axenic conditions at 1 (original), 5, 10, and 15 dS m(-1). The four most effective strains were further evaluated in a pot trial at salinity levels of 1.46 (original), 5, 10, and 15 dS m(-1). In general, salinity depressed the growth of wheat, but inoculation improved the growth and yield of wheat compared with the uninoculated controls. At the high salinity level (15 dS m(-1)), plant height, root length, plant biomass, and grain yield increased upto 37, 70, 116,and 111%, respectively, compared with the control. Results indicated that inoculated plants had higher K+/Na+ ratios, relative water contents and chlorophyll content; however, relatively low proline contents compared with controls. The results also showed that intensity of the classical triple response decreased due to inoculation with these strains. Pseudomonas putida (W2) and P fluorescens (W17) were the most effective strains for alleviating salt stress even at higher salinity levels. Our results suggest that the assay for ACC-deaminase activity could be an efficient approach to screen effective PGPR for increasing the growth and yield of wheat under salt-stressed conditions.