| dc.description.abstract | Symbiotic nitrogen fixation (SNF) can provide an agronomic and economically sustainable
alternative to declining soil fertility and high cost of chemical fertilizers faced by smallholder
farmers in Kenya. The aim of the study was to identify highly effective indigenous rhizobia
for production of commercial bean inoculants and to investigate the influence of bio-char as a
soil amendment on the effectiveness of both indigenous Kenyan rhizobia and commercial
inoculant in symbiosis with common bean in low fertile soils of Western Kenya. Bioprospecting
was conducted in Kenya to collect rhizobia isolates capable of nodulating and
fixing N in symbiotic association with common bean. Three hundred and eighty rhizobia
isolates were recovered from nodules of wild and cultivated legume hosts growing along a
transect of different agro-ecological zones covering about 1045 km transect. These isolates
were authenticated and tested for effectiveness on climbing bean (Phaseolus vulgaris L.) var.
Kenya Tamu in sterile vermiculite, scaling down the number of test isolates to sixteen for
further study. In the greenhouse experiment conducted at the Kabete campus, University of
Nairobi, using soil from Butula in West Kenya two bean cultivars, climbing bean var. Kenya
Tamu and bush bean var. New Rosecoco were inoculated with the 16 promising isolates
which were compared to two widely used commercial inoculant strains, USDA 2667 and
CIAT 899. Out of this experiment, eight most promising isolates including, NAK 5, 45, 67,
92, 104, 157, 186 and 191 were identified to be tested in field trials. Results show that the
isolates did not yield significant differences under field conditions and warrants further
comparison under different field conditions. To investigate the influence of bio-char on the
effectiveness of indigenous rhizobia and commercial strain nodulating common bean, a two
season field expeiment was conducted in Butere and Nyabeda, Western Kenya. There were
no significant differences and interactions observed in biomass production and grain yield
from common beans inoculated with indigenous rhizobia isolates and CIAT 899 with or
without biochar addition in both seasons in both Butere and Nyabeda. Most significant
differences were between managements receiving mineral N and those receiving inoculant
suggesting effective management of N fertilizer and little difference between the candidate
elite strains. While the effect of biochar addition was not significant in relation to inoculation,
there are very strong trends suggesting benefits from adding 2 t ha-1 biochar. Genetic diversity
and phylogeny of the elite Kenyan rhizobia isolates nodulating common bean and soybean
(Waswa et al., 2014) was assayed using the Polymerase Chain Reaction-Restriction Fragment
Length Polymorphism (PCR-RFLP) of the 16S-23S rDNA intergenic spacer region and 16S
rRNA gene sequencing. A phylogenetic tree derived from the partial sequences of the 16S
rRNA gene by neighbor-joining analysis confirmed the greater relationship of indigenous
strains of Bradyrhizobium to reference strains of B. elkanii, B. japonicum and
Bradyrhizobium spp. and a greater relationship of indigenous strains of Rhizobium to
reference strains of Rhizobium sp., Rhizobium tropici and Rhizobium phaseoli. The study
results suggest that continual isolation and characterization to identify elite isolates and use of
biochar, as a soil amendment, offers an opportunity for improvement of SNF with lesser
limitations geographically to the areas of use | en_US |
