Phenotype characteristics of root nodulating bacteria isolated from woody legume trees grown in Saudi Arabia and their ability to nodulation King Saud University, Natural Plan For Science and Technology (NPST) Thobayet S. Al-Shaharani and Nader D. Shetta Range and Forestry Applied Research Unit, Dept. of Plant Production, King Saud University, Riyadh Tools and Equipment Microbiology laboratory was provided with several equipment such as Atomic Absorption and HPLC, incubator shaker, Alumina flow, PCR set, Freezer -200C , Bathwater, Seed incubator, Water distillation set, Electrophoresis set and Autoclave. Introduction Saudi Arabia is located within the regions of tropical and sub-tropical deserts and Acacias are the most dominant tree species throughout the country. It is possible to find rhizobial strains associate with Acacia species in three regions vary in their climate conditions and these regions are Abha, Madinah and Riyadh where no attention has been given to Acacia species in respect to their relation and behaviour with Rhizobia strains under the different local environmental conditions. Thus a comprehensive study on Acacia is necessary to achieve this goal. The mean track of the project was environment, management, treatment and enhancement of pastures and forests development in Saudi Arabia. Acacia tree species are play an important role in economical and social development, but Acacia tree species are face several problems to growth and reproduction such as overgrazing, wood cutting for fuel, agricultural expansion and hard environmental conditions. Despite the importance of Acacia tree species in Saudi Arabia, no attention has been given to their growth parameters and their root-nodule symbionts especially under local conditions. The project was consisted of two main items, first, Ecological studies of native Acacia tree species and Rhizobium isolates in the selected areas, second, Rhizobium studies in the rhizospere and root nodules of these tree species and its applications in three different regions, eastern area (Madinah), southern area (Abha) and central area (Riyadh) at Saudi Arabia. Methods The project was consisted of two main studies; 1- Ecological studies of native Acacia tree species and Rhizobium isolates in the selected areas. 2- Rhizobium studies in the rhizospere and root nodules of these tree species and its applications. The research was conducted through a series of experiments as describe bellow. A Results All selected sites in Riyadh area had extreme environmental conditions and few tree species can tolerate these conditions. in Riyadh area, the dominant tree species in most studied locations was Acacia tortillis subsp. raddiana followed by Acacia tortilis subsp. tortillas then Acacia gerrardii and, while Acacia ehrenbergiana was located in a few sites. The degradation was noticed in all studied sites and that because the intensive grazing and cuttings. Also the regeneration of trees was very poor. So urgent intervention will be needed to protect the local tree species. Phenotypic ally, the Rhizobium isolates from legume trees grown at Riyadh area are belong to the fast growing groups except one strain isolated from Acacia tortillis subsp. raddiana..The strains showed resistance to antibiotics, temperature, salinity, heavy metals and pH. The isolates from present study may be useful to increase the symbiotic nitrogen fixation in legume trees. This study therefore provides the basis for further research on the phylogeny of Rhizobium strains nodulating the legume trees, as well as their use to improve growth and nitrogen fixation of Acacia species grow in central region of Saudi Arabia. B Objectives The project objectives are: a-To investigate the symbiotic and phenotypic characteristics of root-nodulating Rhizobium bacteria associate with Acacia species. b- To select the effective and competitive strains tolerant to high temperature, drought and salinity to improve nitrogen fixation ability of Acacia species. c- To uncover the biodiversity of Rhizobia under different climatic conditions. d- To Produce a bio-fertilizer agents (Rhizobium strains). Rhizobium strains grown on Yeast Extract Mannitol Agar (YEMA) Media used in the study C Future Work In the next phases of the project, work will testing and studying the physiological and biochemical studies of Madinah and Abah regions. Identification of the Rhizobium isolates from different locations to select the effective strains. Test the host-range and effectiveness of inoculation with Rhizobium on tree seedlings. Test the Nitrogen fixation assays of the isolated nodules from tree seedlings. Growth of Rhizobium strains on the Congo Red and Bromthymol Blue Growth Temperature test Utilization of carbon sources