Nodulation and Nitrogen Fixation Potential of Sesbania Spp. Rhizobia on Sesbania Sesban (L.) Merr. and Rose Coco (Phaseolus Vulgaris L.)
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Date
2018-03
Authors
Makatiani, Emmanuel Tendwa
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Global crop and energy production are fast dwindling inversely to population growth.
Common bean (Phaseolus vulgaris L.) yield has reduced worldwide due to soil
infertility which can be reversed through application of chemical fertilizers. The
chemical fertilizers used to ameliorate nitrogen, phoshorus and potassium are expensive
and cause both deleterious physico‒chemical modification of soil and water mass
eutrophication. The common bean has ability to fix atmospheric nitrogen symbiotically
with rhizobia but only a few effective strains have been recovered from African soils,
most of them ineffective under field conditions. Prospecting from local pool of strains
trapped by wild native species like sesbania can increase the number of elite inoculant
production strains for both species in agroforestry systems practiced under diverse soil
and eco-climatic conditions. The specific objectives of this study were: to assess the
phenotypic and genotypic characteristics of rhizobia from root nodules of East Africa
and Namibia Sesbania spp. (here after referred to as sesbania) using morpho-cultural
characteristics and PCR‒RFLP methods; to assess the nitrogen fixation potential of
sesbania isolates on S. sesban using growth parameters; and to determine the
infectiveness and symbiotic effectiveness of sesbania rhizobia on common beans.
Experiments were carried out at the Kenya Forestry Research Institute,
Muguga‒Nairobi, Kenya. Morpho-cultural techniques were used to characterize and
cluster 128 presumptive sesbania rhizobia collected from Kenya, Uganda, Tanzania and
Namibia. The diverse growth characteristics of rhizobia on YEMA media, intrinsic
antibiotic resistance and salt tolerance were used to select for 79 sesbania isolates that
were later subjected to fingerprinting assays using PCR‒RFLP of the 16S rDNA in
comparison with 17 reference strains. The presumptive sesbania rhizobial isolates were
used to inoculate S. sesban and common bean under glasshouse controlled conditions to
test for their infectiveness and symbiotic effectiveness. Reference inoculants strains
KFR647 and BA37 for S. sesban and bean respectively, were included in the test.
Uninoculated positive control (70 ppm N as KNO3) and a negative control (0 ppm N)
were included for strain effectiveness comparison and to check for contamination. The
sesbania rhizobia were grouped into nine morphotypes and various ribotypes per site.
The rhizobia varied in their infectiveness and symbiotic effectiveness on S. sesban and
the common bean resulting in three categories viz: (1) highly effective (2) effective and
(3) ineffective. The mean shoot dry weight, nodule number and nodule dry weight were
all significantly different (p < 0.001). The shoot N content range was 0.16‒5.66 mg
plant-1 and 0.34‒3.08 mg plant-1 for S. sesban and common beans at 8 and 4 weeks of
growth respectively. Based on shoot dry weight due to inoculation, rhizobial isolate
KFR402 was preferred as a common inoculant production strain for both common beans
and S. sesban. However, data in the present study shows that the highest shoot dry
weight was obtained with strain MASS133 (S. sesban) inoculated on Rose coco bean
variety (0.87 g plant-1) and MASS172 (S. sesban) on S. sesban (1.06 g plant-1). Rhizobia
recovered from sesbania grown in East Africa and Namibia are phenotypically and
genetically diverse. The isolates exhibit great variations in effectiveness and nitrogen
fixation efficiency on S. sesban and common beans (variety: Rose coco). Prospecting for
elite rhizobia inoculant strains should be prioritized and tested for effectiveness on both
S. sesban and common bean grown in diverse edaphic and agro-ecological conditions
under agroforestry systems.
Description
A thesis submitted in partial fulfillment 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. March, 2018