Diversity of non-rhizobial bacteria from nodules of Melilotus indicus L. and their plant growth promotion ability

Abstract

Seventy-four isolates of the non-rhizobial endophytic bacteria obtained from nodules of wild legume Melilotus indicus L. collected from nine different Egyptian soils. Diversity of these isolates was studied based on their morphological and physiological characteristics. Additionally, their growth promoting activity assessed based on production of indole acetic acid (IAA) ammonia, hydrogen cyanide (HCN), solubilization of phosphorous (P), fixation of nitrogen in culture media and antibiosis of pathogenic fungi. The isolates showed different colony shapes. The isolates were gram-positive being rod in shape. Bacterial isolates showed a wide diversity in their pH tolerance ranged from three to11 and high tolerance to NaCl up to 10%. All the isolates were unable to grow at 10 °C, while all of them grew at 40°C. Nearly, all the isolates showed high tolerance to the different heavy metals used. Most of the isolates produced IAA and ammonia and about 14% of the isolate had the ability to fix nitrogen in culture media. Most of the isolates had antagonistic activity against Fusarium oxysporium f. sp. fabae, Fusarium oxysporium f. sp. Lycopersiciand Alternaria alternate. All the isolates cannot solubilize P or produce HCN. In conclusion, the 74 non-rhizobial endophytic bacteria isolates are both phenotypically diverse. Such bacteria might act as plant growth promoting as well as supporting agents within root nodule for both host and rhizobia. In addition, some of these isolates were a diazotroph in culture media and M. indicus can be a potential source of unique endophytic bacteria.