-AMINOCYCLOPROPANE-1-CARBOXYLATE (ACC) ENRICHMENT: AN EFFECTIVE APPROACH TO SCREEN PLANT GROWTH-PROMOTING RHIZOBACTERIA FOR MAIZE

By using enrichment medium containing 1-aminocyclopropane-1-carboxylic acid (ACC) as sole nitrogen source, 21 strains were isolated from the maize rhizosphere in two phases i.e., 9 isolates in first phase and 12 isolates in second phase. Two trials in glass jars were conducted under gnotobiotic conditions to select effective plant growth-promoting rhizobacteria (PGPR). All the 21 isolates tested in both the trials exhibited growth promoting activity in maize but with variable degree of efficacy. Among the 9 isolates tested in 1st trial, isolate Q14 caused an increase of 7.1-folds in root elongation over uninoculated control. Shoot length and seedling fresh weight (root + shoot) were increased up to 7.0-and 2.0-folds, respectively, over uninoculated control in response to inoculation with Q7. In the 2 nd trial, rhizobacterial isolate Q30 was found to be the most effective as its inoculation resulted in 2.8-, 2.0-and 1.7-folds increase in root elongation, shoot length and seedling fresh weight (root + shoot weight), respectively, over uninoculated control. The growth promoting activity exhibited by the rhizobacteria might be due to their ability to hydrolyze ACC, thus resulting in decreased endogenous ethylene synthesis, which eliminated the potential inhibitory effects of higher ethylene concentrations. Results showed that use of ACC-enriched medium is an effective and efficient approach to select promising PGPR