PGPR Characterization of Non-Nodulating Bacterial Endophytes from Root Nodules of Vigna unguiculata (L.) Walp.

Abstract

Seventeen morphological groups of Non-Nodulating Endophytic Bacteria (NNEB) were isolated from the interior of healthy cowpea root nodules (Vigna unguiculata L. Walp.) growing in seven soils from three regions of Peru. The amplification and partial sequencing of the 16S rRNA ribosomal gene for representatives of each morphological group showed that they were closely related to members of genera Rhizobium, Agrobacterium, Phyllobacterium, Mesorhizobium, Bosea, Ochrobactrum, Bradyrhizobium, Labrys, Ensifer, Starkeya and Nordella (Proteobacteria), and of Mycobacterium (Actinobacteria). The plant growth promotion capacity of representative NNEB strains was examined. Agrobacterium radiobacter 5620I and 5722H isolates showed high IAA production (> 400 μg ml−1). Ochrobactrum haematophilum 5410F and Starkeya novella 5740O were the best isolates solubilizing tricalcium phosphate (> 300%). Agrobacterium radiobacter 5722H was the best isolate for production of siderophores (272.59%), whereas A. radiobacter 5620I showed the greatest antagonistic activity against Fusarium oxysporum (88.52%). The NNEB strains identified in this study showed that cowpea root nodules are a potential source of Plant Growth Promoting Bacteria (PGPB) which may be used for the development of new inoculants.