Phenotypic characteristics and composition of rhizobia associated with woody legumes growing in diverse Kenyan conditions

• Published in: Plant and soil 1997-01, Vol.188 (1), p.65-75
• Main Authors: Odee, D.W. (Kenya Forestry Research Inst., Nairobi (Kenya). Biotechnology Div.), Sutherland, J.M, Makatiani, E.T, McInroy, S.G, Sprent, J.I
• Format: Article
• Language: English
• Subjects: ACACIA; Acid soils; Agar; Agronomy. Soil science and plant productions; Animal, plant and microbial ecology; Antibiotic resistance; Antibiotics; Bacteria; Bacteriology; Biological and medical sciences; BRADYRHIZOBIUM; Data processing; Desert soils; Economic plant physiology; FENOTIPOS; Fundamental and applied biological sciences. Psychology; Growth rate; KENIA; KENYA; Legumes; Mannitol; Media (isolation); Microbial ecology; Microbiology; Milk; Minerals; Nodules; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Phaseolus vulgaris; PHENOTYPE; PHENOTYPES; Polysaccharides; RHIZOBIUM; Roots; Salts; Savanna soils; SESBANIA; Sodium chloride; Soil; Soil ecology; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Yeasts
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1023/A:1004204413140

Over 480 rhizobia were isolated from root nodules of woody legume and herbaceous trap host species grown in soils collected from 12 different Kenyan sites. The isolates were differentiated by growth and morphological characteristics, intrinsic antibiotic resistance (IAR) and salt (NaCl) tolerance levels (STL) when grown on yeast mannitol mineral salts agar and broth media. The bulk of the isolates (91%) were watery, milky-translucent and curdled milk types with moderate to copious extracellular polysaccharide (EPS). The rest were creamy or white opaque with little to moderate EPS production. Overall, they showed a wide range of growth rates: very fast-growing (mean generation time 1.6-2.5 h), fast-growing (2.8-4.8 h), intermediate between fast-and slow-growing (5.6-5.7 h) and slow- and very slow-growing (6.4-8.8 h). The isolates were tentatively grouped into Rhizobium spp., to include very fast, fast and intermediate (acid-producing) types; and Bradyrhizobium spp., to include very slow, slow and intermediate (alkali-producing) types. Bradyrhizobium spp. were more sensitive to antibiotics (40 µg mL⁻¹) than Rhizobium spp., contrary to the general opinion which indicates that they are normally resistant. Cluster analysis based on sensitivity responses of IAR and STL could not distinguish Rhizobium spp. from Bradyrhizobium spp., neither was there any association by site nor host of isolation except for those isolates trapped with Phaseolus vulgaris at Kibwezi. Our data demonstrated a high diversity of tropical rhizobia associated with trees.