Identification and Characterization of Rhizobium Associated with Woody Legume Trees Grown under Saudi Arabia Condition

Six woody legume tree species, Acacia ehrenbergiana (Hayne.), Acacia nilotica (Willd.), Acacia saligna (Labill.), Acacia tortilis (Forssk.), Acacia tortilis var. reddiana ( Savi.) and Leucaena leucocephala (Lam.) were performed the growth characteristics and to identify the resistance of native isolated Rhizobium strains from root zone surrounding trees to environmental stressesantibiotic, high temperature, salinity and acidity. Physiological properties of all isolated strains were fast growing and had the same colony morphology and produced high, slimy/mucous transparent to creamy colored colonies on YEMA plates after 3 days of incubation at 28°C. In addition to the strains failed to absorb Congo Red stain in the medium except for those isolated from L. leucocephala (LLR). Acid production was observed among the isolates after 72 hours. The generation span or longevity for YEMB cultures at 28°C ranged between 2.07 and 3.85 hours. The strains showed ability to the resistance of antibiotics, temperature, salinity and pH fluctuation. Based on the utilization of carbon and nitrogen as sole source of carbon and nitrogen, the results showed that those strains probably belonging to one of two groups, Rhizobium or Sinorhizobium. The isolates from present study may be useful to increase the symbiotic nitrogen fixation in legume trees. Therefore the study provides basis for further research on the phylogeny of Rhizobial strains nodulating the legume trees, as well as their use as inoculants to improve growth and nitrogen fixation in arid lands of the central region of Saudi Arabia.