American-Eurasian J. Agric. & Environ. Sci., 10 (3): 410-418, 2011 ISSN 1818-6769 © IDOSI Publications, 2011 Corresponding Author: N.D. Shetta, Plant Production, Food and Agriculture Sciences College, King Saud University, KSA. E-mail: n.shetta@yahoo.com / nshetta@ksu.edu.sa. 410 Identification and Characterization of Rhizobium Associated with Woody Legume Trees Grown under Saudi Arabia Condition N.D. Shetta, T.S. Al-Shaharani and M. Abdel-Aal Department of Plant Production, Food and Agriculture Sciences College, King Saud University, KSA Abstract: 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 stresses- antibiotic, 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. Key words: Woody legume trees Rhizobium characteristics Identification Environmental stress KSA INTRODUCTION species identified as potential N fixers [3]. Nowadays, Nutrient enrichment of soils by nitrogen fixing and semi arid temperate zones are major sources of N in symbiotic bacteria present in legumes has been known for semi-arid, arid and desert ecosystems: sequential centuries. Scientific demonstration of this symbiosis was cropping systems, agroforestry and silvopastoral systems started in 19th century and it established the facts that (pastoralism), providing timber, fuel, pulp, fodder and bacteria present in nodules on legume roots are even human food. Various published studied have been responsible for fixing atmospheric nitrogen [1]. Rhizobium discussing the establishment and functioning of NFTs spp. are well known group of bacteria that acts as the symbiosis [4]. The classical phenotypic characterization primary symbiotic fixer of nitrogen. These bacteria infect of Rhizobia has often been the first method employed the roots of leguminous plants, leading to the formation when classifying unknown strains of Rhizobia [1, 5]. of lumps or nodules where the nitrogen fixation takes Though this method provides valuable information, it is place. The bacterium’s enzyme system supplies a laborious and time consuming. The Biology system, constant source of reduced nitrogen to the host plant and which is based on metabolic fingerprinting by the plant furnishes nutrients and energy for the activities determination of carbon source utilization, offered a less of the bacterium. This symbiosis reduces the requirements tedious alternative for large scale screening of isolates. It for nitrogenous fertilizers during the growth of has been used to characterize and classify bacteria and leguminous crops [2]. Legumes are regarded as the third bacterial communities in a wide range of environments, largest family of angiosperm plants, including 17 000–19 including marine, agricultural and nonagricultural soils 000 species distributed world-wide with nearly 3000 and sludge [6, 7] The biology method has, for example, 2 introduced woody species from their tropical origin to arid