Plant Archives Volume 20 No. 2, 2020 pp. 5951-5957 e-ISSN:2581-6063 (online), ISSN:0972-5210 PHENOTYPIC CHARACTERIZATION OF RHIZOBIAL STRAINS SYMBIOTICALLY ASSOCIATED WITH PROSOPIS SPECIES IN INDIA Garima Bissa*, Nisha Tak and Hukam S. Gehlot BNF & Microbial Genomics Lab, Department of Botany, Center of Advanced Study, Jai Narain Vyas University, Jodhpur, (Rajasthan), India Abstract With the increasing desertification, legume-rhizobia symbiosis has been found to be a considerable contributor of fixed nitrogen specifically in the arid and semi-arid soils. In the present investigation, root nodule bacteria were isolated by trapping two legumes, Prosopis cineraria and Prosopis juliflora in soils collected from five sampling sites in India. A total of 32 strains were purified, most of them were fast-growing and two were slow-growing. Ten strains were selected for phenotypic characterization including nine fast-growing and one slow-growing. Strain JNVU PJ1 tolerated up to 5% (w/v) NaCl while most of them could survive up to 2%. All the strains survived at pH range of 6–11 and temperature up to 45°C, while few could grow even at 50°C. Most of the strains were sensitive to antibiotics Ciprofloxacin, Gentamycin, Kanamycin, Neomycin, Streptomycin and Tetracycline; and resistant to Erythromycin. Strains were diverse in terms of utilizing different sugars as sole carbon source. Dextrose was utilized by maximum number of strains (6 strains) and trehalose by 5 strains of the 10 tested. None of them could utilize galactose and inositol. These phenotypic traits and metabolic capability play an important role in survival of rhizobia in stressed conditions. The Prosopis-rhizobial strains showing phenotypic and metabolic diversity can be used as inoculums in various agroforestry programs for improving nitrogen content of the depleting soils. Key words: Prosopis, Legume, rhizobia, phenotypic traits Introduction The most important limiting factor for crop production is nitrogen. Biological Nitrogen Fixation (BNF) has been found to be a great contributor of fixed nitrogen in the terrestrial ecosystems, as it contributes at least 70 million tons of nitrogen every year (Peoples et al., 1995). Increasing desertification is one of the major effects of global climate change, thus, studying legume-rhizobia combinations that are well adapted to survive in environmental stresses like drought, high temperature and salinity, would be helpful in selecting the inoculants that could survive and contribute to the fixed nitrogen in the arid and semi-arid deserts (Atieno and Lesueur, 2019). Both high and low temperature beyond the optimum range of 25-30°C that is suitable for rhizobia, affects the nodulation and nitrogen fixation in the legumes adversely (Zhang et al., 1995). Thus, screening of rhizobia capable of enduring at high temperatures would be helpful in selecting tolerant strains to be used as inoculants especially in the dry arid regions. Antibiotics are another important marker for selection of efficient rhizobial inoculants as well as for characterization/identification of rhizobial strains at phenotypic level knowing that resistance and susceptibility to antibiotics is quite related with the symbiotic effectiveness (Schwinghamer and Dudman, 1973; Kremer and Peterson, 1982). Tree legumes, like species of Acacia and Prosopis that are abundant in the arid and semi-arid deserts prove to be good agent for soil stabilization and nitrogen fixation in association with both fast-growing as well as slow- growing rhizobia (Zhang et al., 1991). The genus Prosopis (Tribe, Mimoseae) comprises of approximately 44 known species (Burkart, 1976) and most of the genera belong to arid and semi-arid deserts of America, while very few belong to Africa and Asia (Catalano et al., 2008). Basak and Goyal (1980) suggested 0.8–1.8% as optimum range of salt for survival of rhizobia isolated from tree legumes including P. cineraria, similarly temperature range in which rhizobia could best survive was 35–40°C; the pH values below 4 and above 10 was *Author for correspondence : E-mail : bissa.garima2@gmail.com