Symbiotic efficiency and diversity of native rhizobia isolated from climbing beans (phaseolus vulgaris l.) in Embu and Tharaka Nithi Counties, Kenya
Date
2016-11
Authors
Koskey, Gilbert
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Kenya is the eighth highest producer of common beans (Phaseolus vulgaris L.)
worldwide with a production of 529,265 tons annually. Climbing beans are highly
productive, and can produce yields 2 to 3 times higher than bush beans and is
therefore a promising option to increase bean yields in Kenya. However, climbing
bean production is greatly affected by the decline in soil fertility, particularly low
nitrogen levels in the soil. Replenishment of soil nitrogen using effective rhizobia
inoculants presents a sustainable solution to climbing bean production. The objectives
of this study were to assess climbing bean varieties grown by smallholder farmers in
Eastern Kenya, to determine the genetic diversity of native rhizobia strains that
nodulate climbing beans and to determine nodulation and symbiotic nitrogen fixation
efficiencies of native rhizobia strains isolated from climbing beans grown in Eastern
Kenya. Questionnaires were used to obtain information on climbing bean varieties
grown in Eastern Kenya. The experiments involved laboratory analysis, greenhouse
and on farm activities. A complete randomized design and a randomized complete
block design were used in the greenhouse and field experiments respectively. Five
climbing bean varieties were identified in Embu and Tharaka Nithi Counties of
Eastern Kenya; Gatune, Raila, Mama safi, Kithiga and Muviki, of which Gatune was
the most preferred variety. In regards to bean diversity, Embu Lower Midland zone
had the highest Shannon-Wiener diversity index (H) of 2.01, while Embu Upper
Midland zones had the lowest diversity index (H) of 1.83. From the laboratory
analysis, 41 native rhizobia isolates were isolated from the root nodules of midaltitude
climbing beans (MAC 13 and MAC 64) and placed into 9 groups based on
their morphological characteristics. Rhizobia diversity was determined based on
restriction digestion ofPCR amplified 16S rRNA genes using Msp I, EcoR I and Hae
III enzymes. Analysis of molecular variance based on restriction digestion of 16S
rRNA genes showed that there was a 100 % genetic variation within population and
no variation (0 %) among the four rhizobia populations and across the two regions (0
%). Nine representative native rhizobia isolates were tested in the greenhouse for their
symbiotic nitrogen fixation efficiency on MAC 13 and MAC 64 climbing bean
varieties. Four native isolates ELM3, ELM5, ELM8 and ELM4 with symbiotic
efficiency (SE) of 123.72%,99.21%,98.24% and 96.75%, respectively, compared
favorably with the commercial rhizobia inoculant (Biofix-CIAT 899) (SE of 95.21%).
The best native rhizobia isolate (ELM3) was evaluated in the field experiment using
MAC 13 and MAC 64 climbing beans. The mean nodule number of climbing beans
differed significantly (p < 0.0001) among the test isolates. Climbing beans inoculated
with test isolate ELM3 recorded a higher mean nodule number (85.58 plant")
compared to the Biofix-CIAT 899 (76.13 plant") and non-inoculated control plants
(52.08 plant"). There was a significant effect of rhizobia isolates on shoot dry weight
(p < 0.0001) and total bean seed yield (p < 0.0001). Climbing beans inoculated with
native isolate ELM3 produced the highest mean seed yield of 4,397.75 kg/ha,
indicating 89 % increase over non-inoculated control which yielded 2,334.81 kg/ha.
This study demonstrated the presence of diverse native rhizobia isolates that are
potentially superior over the commercial inoculant (Biofix-CIA T 899) bean
inoculants. However, these isolates need to be identified and tested further in different
geographical locations to determine their efficiency and stability on bean production.
Description
A thesis submitted in partial fulfilment of the requirements for the award of the degree of Master of Science (microbiology) in the school of pure and applied sciences of Kenyatta University.
NOVEMBER, 2016