Abundance and Symbiotic Rhizobia Colonizing Soybean (Glycine max) in Soils of Kakamega County, Western Kenya

Abstract

Identification of effective indigenous rhizobia strain nodulating soybean (Glycine max) was conducted in Kakamega County, Western Kenya. This study was carried out to establish the abundance and symbiotic efficiency of native rhizobia strains in soil samples collected from 12 sites in four agroecological zones within the region. The MPN enumeration technique was used to estimate the indigenous rhizobia numbers and showed that 54% of the sampled sites had high abundance. Rhizobia number in the soil collected from the six regions varied from 2.5 × 102 to 3.12 × 103 cells·g− soil. Thirty isolates from the soil collected in the four regions were tested for efficiency using soybean as the trap plant in Leonard jars containing sterilized vermiculite irrigated with nitrogen-free media. Determination of the relationship between rhizobial abundance and symbiotic efficiency with respect to the soil chemical conditions was performed using ANOVA, and the means were compared using Tukey’s honest significant difference test. Inoculation with bacterial isolates significantly ( P < 0.05 ) increased the nodule number and shoot dry weight, while weight of the seeds showed variations across the groups. The soil pH across the 4 regions ranged between 5.41 and 6.52.

Distribution, Characterization and the Commercialization of Elite Rhizobia Strains in Africa

“…In the dark, rhizobia stand out as white, translucent, glistening, elevated, tiny colonies with an entire margin, in contrast to the red-stained colonies of Agrobacterium when grown in the dark [ 131 ]. Since all rhizobia are positive for catalase, indole, citrate, and oxidase tests, they are often used to distinguish rhizobia from other bacteria [ 80 , 100 , 132 ].…”

“…Biological nitrogen fixation is effective in neutral or slightly acidic soils [ 98 ]. However, most African soils are acidic because of industrial pollution and poor agricultural practices, such as the overutilization of inorganic fertilizers ( Figure 4 ) [ 8 , 100 ]. In general, acidic soils negatively affect crop production [ 67 , 101 , 102 ] and the proliferation of soil bacteria.…”

“…In particular, low pH promotes Al toxicity [ 103 ], which is more detrimental to rhizobia than acidity or phosphorus and calcium deficiencies [ 104 ]. At pH 5.4, Kawaka et al [ 8 ] found Al concentration as high as 2.8 Cmol/kg, and Mulama et al [ 100 ] found 1.2 Cmol/kg in Kenyan soils. In particular, exposing rhizobia to Al over extended periods of time has long-term negative consequences on the rhizobia population and its growth [ 105 ].…”

The Cell Membrane of a Novel Rhizobium phaseoli Strain Is the Crucial Target for Aluminium Toxicity and Tolerance

“…This variability calls for an independent investigation of rhizobia from a specific location when investigating their Al tolerance. For those studies, western Kenya soils are interesting and economically important because they possess pH as low as 4.9 and Al concentrations as high as 28 mM [ 28 , 29 ]. Commercially available rhizobia strains, such as the CIAT899, do not colonize common bean plants very well in Kenyan soils [ 28 , 30 ].…”