Population Level of Bean Rhizobia in the Soil of Semi-Arid South-East Kenya and Assessment of Symbiotic Behaviour
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Date
2001
Authors
Maingi, J.M.
Shisanya, C.A.
Gitonga, N.M.
Hornetz, B.
Journal Title
Journal ISSN
Volume Title
Publisher
Faculty of Science Kenyatta University
Abstract
The major objective of this study was to investigate Biological Nitrogen Fixation (BNF) in
common bean in semi-arid south-east Kenya. The population of indigenous rhizobia specific to
common bean was determined using the Most Probable Number (MPN) plant infection
technique. The experimental design was randomised complete block design (RCBD) with four
replications per treatment. The results of the MPN count indicated that the number of
indigenous rhizobia resident in Kiboko soils, and specific to common bean were 2,037 - 14,850
rhizobia cells per gram of soil. Isolation carried out from the nodules indicated two different
types of isolates. One has small and dry colonies (CIS), while the other one had large mucoid
colonies (C2L). Presumptive and authentication tests confirmed these isolates as rhizobia.
Indigenous rhizobia were isolated from the common beans grown in Kiboko soil and tested for
ability to fix nitrogen in comparison to a commercially available Rhizobium strain 446 from
MIRCEN, University of Nairobi. Results showed that infectivity in common bean with
Rhizobium strain 446 was good (80 nodules/plant). Bisection of the nodules showed that only
32 % of them had an inner pink colour. This is an indication that a majority of the nodules were
not effective in fixing nitrogen hence the need to frequently re-evaluate the homogeneity of the
commercial strain 446. Greenhouse trials showed that isolate CIS was not effective in nitrogen
fixation and that Rhizobium leguminosarum bv. phaseoli strain 446 and C2L from MlRCEN and
soils ofSE-Kenya, respectively, were superior in nitrogen fixation compared to CIS
Description
Research Article
Keywords
common bean, Rhizobium, semi-arid, south-east Kenya
Citation
East African Journal of Science 3(1): 13-18 (2001)