Abundance and morphological characteristics of rhizobia nodulating common bean in Uganda

We used the plant infection technique to estimate the population of rhizobia in soils obtained from the Montane and Mt. Elgon agro-ecological zones (AEZs), focusing on three land use management practices across an elevation gradient. There were larger numbers of bean-nodulating bacteria (shown by the MPN range) in cultivated land as compared to forest and grassland (Table 1).

With a minimum of 20 isolates per soil sample, 500 isolations were made from bean nodules. The following colony morphologies were observed; white, opaque and raised (70%) and white, translucent and raised (30%) with a colony diameter ranging from 1.0-2.0 mm after 2-3 days. Less than 10 colonies had a colony diameter ranging from 3.0-4.0 mm. The isolates were stored in a broth-glycerol mixture for further work and also used in subsequent authentication experiments.

From the authentication experiments under sterile conditions in a growth chamber for 133 isolates, 244 out of 266 duplicate runs generated a positive authentication giving a nodulation efficiency of 91.7%. Future work will involve DNA sequencing and effectiveness tests of the isolates in comparison with commercial inoculants.

Figure 1. (a) Isolation of rhizobia on YEMA-CR media and (b) sterile nutrient solution addition during authentication tests of the isolates in a growth chamber


Allan Ochieng, Wageningen University, The Netherlands (Click here for his 2015 update)

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