Wild legumes (herb or tree) are widely distributed in arid regions and actively contribute
to soil fertility in these environments. The N2-fixing activity and tolerance to drastic
conditions may be higher in wild legumes than in crop legumes. The wild legumes in
arid zones harbor diverse and promiscuous rhizobia in their root-nodules. Specificity
existed only in few rhizobia from wild legumes, however, the majority of them are
with wide host range. Based on phenotypic characteristics and molecular techniques
(protein profiles, polysaccharides, plasmids, DNA-DNA hybridization, 16SrRNA, etc.),
the root-nodule bacteria that was isolated from wild legumes had been classified into
four genera (Rhizobium, Bradyrhizobium, Mesorhizobium and Sinorhizobium). The rhizobia
of wild legumes in arid zones, exhibit higher tolerance to the prevailing adverse
conditions, e.g. salt stress, elevated temperatures and desiccation. These rhizobia
may be used to inoculate wild, as well as, crop legumes, cultivated in reclaimed desert
lands. Recent reports indicated that the wild-legume rhizobia formed successful symbioses
with some grain legumes. Moreover, intercropping of some N2-fixing tree legumes (e.g.
Lablab, Leucaena, Sesbania, etc.) to pasture grasses improved biomass yield and herb
quality. In recent years, the rhizobia of wild legumes turn the attention of biotechnologists.
These bacteria may have specific traits that can be transferred to other rhizobia
through genetic engineering tools or used to produce industrially important compounds.
Therefore, these bacteria are very important from both economic and environmental
points of view.