Morphological and Biochemical Characterization of Soybean Nodulating Rhizobia Indigenous to Zambia

Abstract

Soybean [Glycine max (L.) Merrill] is known for nitrogen fixation by rhizobia present in the soil with which it establishes an efficient symbiosis. In Zambia, current rhizobial inoculants used in soybeans production are based on non-indigenous strains; this creates a need to isolate local strains that can be used for the development of local inoculants for soybeans in Zambian soils. This paper reports the isolation and characterization of rhizobial isolates from virgin and cultivated soils of the three agro-ecological regions of Zambia. Rhizobia were isolated using the Trap Method and characterized using selected morphological and biochemical markers. A total of 61 isolates were isolated on Yeast Extract Mannitol (YEM) agar medium. Isolates varied in colony form, color, margin and texture. From the 61 isolates from the three regions, 87 % were circular, 8 % irregular and 5 % punctuate in form with 100 % convex elevation. The isolates had 88% entire, 10% undulate and 2 % lobate colony margins with different colors -56 % cream, 24 % white, 11 % yellow, 5 % transparent and 3 % pink. Transparent colonies were peculiar to Region I and III while pink colonies were peculiar to Region III. All isolates produced mucous, were gram negative and rod shaped, a characteristic of rhizobial cells. None of the isolates could tolerate extremes of pH (4 and 9) in growth medium but grew well at pH 6.8. All isolates utilized glucose as a source of carbon. Based on the Bromothymol Blue (BTB) assay, 59 isolates were fast growing while two isolates from cultivated soils of region II were slow growing. The fast growing 59 isolates showed an acidic reaction changing the medium from green to yellow, while the others showed an alkaline reaction. Based on the results, the 59 fast-growers could be Ensifer fredii or/and Rhizobium tropici rather than Bradyrhizobium. However, further tests to confirm these findings using ketolactose, genetic characterization and inclusion of reference strains, are still needed and are being recommended here.

Isolation, characterization and symbiotic performance evaluation of soybean (Glycine max) nodulating rhizobia from different districts of Bangladesh

“…However, the strain SB-212 yielded the maximum plant growth according to dry mass though its nodule number and nodule mass were not the highest. Similar results also observed by Chibeba et al (2017), Habibi et al (2017) and Kapembwa et al (2016). In the present study, the nodule dry mass of each plant was not evenly proportioned with their respective nodule number because the nodule size was not similar.…”

Differential traits of rhizobia associated to root-nodules of gum acacia (Senegalia senegal), shittah tree (Vachellia seyal), pigeon pea (Cajanus cajan L) and cowpea (Vigna unguiculata)

“…Isolates were tested Gram negative and were microscopically rod-shaped and pink in colour after treatment with iodine reagent, confirming that they belonging to the genus Rhizobium. Related results were obtained respectively from Arachis hypogaea L. and Telfairia occidentalis in Nigeria (Agah et al, 2016), from Glycine max L. in Zambia (Kapembwa et al, 2016), from Mucuna pruriens L. in Nepal (Paudyal and Gupat, 2017), from V. mungo L. and V. radiata L. in India (Tyagi et al, 2017). These isolates were also recognized as acid producers, since they shifted the green colour of Bromothymol blue to yellow when incubated at 28±2°C for 3 days (Table 2).…”

Evaluation of Physiological Properties of Winged Bean Rhizobium and Its Comparison with Other Rhizobia

“…However, moong showed better adaptability in pH between 5.0 and 7.0. Investigation carried out by different workers on Rhizobium isolated from root nodules of different crop viz., Rhizobium trifolii, R. phaseoli, R. leguminosarum and Bradyhizobium japonicum revealed the fact close to observation made in the present study (Bhatt et al, 2013;Dutta et al, 2015;Rai andSen, 2015 andKapembwa et al, 2016).…”