Isolation and screening of rhizobacteria containing ACC- deaminase for growth promotion of sunflower seedlings under axenic conditions

The use of rhizobacteria containing 1-Aminocycloprpane-1- carboxylic acid (ACC) deaminase may have beneficial effect on plant growth by regulating endogenously synthesized ethylene. Forty isolates of rhizobacteria containing ACC-deaminase were isolated by using dilution plate technique and screened for growth promotion of sunflower seedlings under axenic conditions. Selected isolates revealed the differential ability to utilize ACC as sole N source. On the basis of determined ACC qualitative assay, 12 isolates were noted for highest, 15 medium and 13 lower ACC-deaminase activity. The results showed that 31 isolates (out of 40) increased the root length, shoot length, root fresh weight, shoot fresh weight, root dry weight and shoot dry weight up to 58, 63, 71, 53, 67 and 55%, respectively, over uninoculated control, while 9 isolates had negative effect on root and shoot growth as compared to control. The isolates showing positive effects were taken as plant growth promoting rhizobacteria (PGPR) for further experimentation. The results indicated that screening effective isolates of rhizobacteria containing ACC-deaminase for growth promotion of sunflower under axenic conditions could be a valuable approach for selecting efficient isolates before testing their potential under natural conditions.