ABSTRACT
Five Rhizobium strains (Cb1, Cb2, Cb3, Cb4 and Cb5) were isolated from root nodules of cluster bean [Cyamopsis tetragonoloba (L.)] on yeast extract mannitol agar (YMA) medium. All the five Rhizobium isolates have shown the Indole Acetic Acid( IAA) production in culture medium supplemented with L-tryptophan. The IAA content in culture supernatant was estimated by using the colorimetric method (13). All the five Rhizobium isolates produced maximum amount of IAA in medium supplemented with 2.5mg/ml Ltryptophan concentration. Production of IAA was maximum at 72h of incubation when bacteria reached the stationary phase. The cultural conditions were optimized for maximum IAA production by using different carbon and nitrogen sources as well as changing the incubation period. Glucose and L-asparagine were found to be the best carbon and nitrogen sources, respectively for maximum IAA production. The cell wall affecting agent, penicillin increased the IAA production up to 77.95% in Cb4, 59.52% in Cb5 and 37.84% in Cb3 isolates, over the control. Among the five isolates studied, isolate Cb4 showed better performance in IAA production.