Abstract

Rhizobia could exhibit plant growth-promoting mechanisms besides nitrogen fixation. In search of efficient rhizobia with multiple PGP traits, 72 groundnut nodulating rhizobia isolates were screened in vitro for their plant growth promoting traits like phosphate solubilization, production of indole acetic acid, ammonia, hydrogen cyanide, production of different hydrolytic enzymes and antifungal activity. About 72% of the isolates produced IAA, varying from 7.4 to 78.8 μg.ml⁻¹ and 23.6% of the isolates were able to solubilize tri-calcium phosphate. Even if all isolates could produce ammonia, two isolates were strongly produced. Only two isolates were able to produce hydrogen cyanide. The enzymatic production study revealed that 50 and 48% of the tested isolates showed protease, and cellulase activities respectively. Only 13.8% of the isolates were found to be inhibitory against the test pathogen, Fusarium oxysporum, but the maximum inhibition potential was exhibited by GNR-07. The present study also demonstrated that 100% of the isolates exhibited multiple PGP (plant growth promotion) properties, with isolates GNR-37 and GNR-28 being superior, acquiring the highest number of PGP properties (87.5% each). These isolates can be potential candidates as a PGPR inoculant after evaluation of their performance under greenhouse and field conditions.

Key words: Rhizobia isolates, plant growth-promoting traits, enzymes and some chemical compound production, antifungal activity.