Omwoyo Ombori

Symbiotic Efficiency of Native Rhizobia Nodulating Common Bean (Phaseolus vulgaris L.) in Soils of Western Kenya.

This study was conducted to determine the abundance and symbiotic efficiency of native rhizobia nodulating common bean in Kisumu and Kakamega, Kenya. Soil sampling was carried out in three farms that had been used for growing common bean for at least two seasons and one fallow land with no known history of growing common bean or inoculation. Abundance of soil rhizobia and symbiotic efficiency (SE) were determined in a greenhouse experiment. Native rhizobia populations ranged from 3.2 × 101 to 3.5 × 104 cells per gram of soil. Pure bacterial cultures isolated from fresh and healthy root nodules exhibited typical characteristics of Rhizobium sp. on yeast extract mannitol agar media supplemented with Congo red. Bean inoculation with the isolates significantly (p < 0.05) increased the shoot dry weight and nitrogen (N) concentration and content. The SE of all the native rhizobia were higher when compared to a reference strain, CIAT 899 (67%), and ranged from 74% to 170%. Four isolates had SE above a second reference strain, Strain 446 (110%). Our results demonstrate the presence of native rhizobia that are potentially superior to the commercial inoculants. These can be exploited to enhance bean inoculation programmes in the region.

Isolation of High Antibiotic Resistant Fecal Bacteria Indicators, Salmonella and Vibrio Species from Raw Abattoirs Sewage in Peri-Urban Locations of Nairobi, Kenya

The research was conducted to determine indicator organisms’ relationship to specific human pathogens and any presence of antibiotic resistance. Isolationof indicator organisms,Salmonella and Vibrio species was carried out using standard laboratory methods. Sensitivity to antibiotics was determined by the agar diffusion technique. The fecal bacteria load was found to be 6.2 x 10 6 , 5.3 x 10 5 , 2.5 x 10 4

Morphological Assessment and Effectiveness of Indigenous Rhizobia Isolates that Nodulate P. vulgaris in Water Hyacinth Compost Testing Field in Lake Victoria Basin

Aims: The study was aimed at isolating, identifying and assessing the effectiveness of indigenous rhizobia nodulating P. vulgaris in Lake Victoria Basin (LVB). Study Design: Randomized complete block design. Place and Duration of Study: Soil and nodule samples were collected from Kisumu (Kenya); Kabanyolo (Uganda) and Nyabarongo (Rwanda). Field experiments: Kisumu (Kenya). Lab and greenhouse experiments: Department of Plant and Microbial Sciences Kenyatta University (Kenya) and Makerere University (Uganda). Research was carried out between January 2012 and April 2013. Original Research Article British Journal of Applied Science & Technology, 4(5): 718-738, 2014 719 Methodology: Rhizobia were isolated from nodules obtained from P. vulgaris (rose coco variety) plants planted in the LVB water hyacinth compost trial fields and whole soil trapping experiments in the greenhouse using soil obtained from the LVB. The isolates were characterized using morphological features. Isolates from each group were used in authentication using the infection technique. Results: One hundred and twenty eight isolates were obtained from the trapping experiments and placed into nine groups based on their morphological characteristics. Four hundred and seventy two isolates were obtained from the nodules of the P. vulgaris grown in soils amended with water hyacinth compost and were placed into sixteen groups. The isolates varied in their morphological characteristics. There was a significant difference in the infectiveness and effectiveness of the representative rhizobia isolates. Conclusion: The studies revealed that rhizobia isolates from Lake Victoria are different morphologically. Authentication experiments, confirmed that the majority of the isolates were rhizobia due to their ability to infect the host plant P. vulgaris. All representative isolates varied in their ability to infect and fix nitrogen. Isolates that are more effective compared to the commercial Rhizobium leguminosarum biovar phaseoli strain 446 were isolated in this study. The effective indigenous rhizobia have therefore the potential of being sources of inocula for P. vulgaris.

Cost-effective Nutrient Sources for Tissue Culture of Cassava (Manihot esculenta Crantz)

Application of tissue culture technology is constrained by high costs making seedlings unaffordable. The objective of this study was to evaluate the possibility of using locally available fertilizers as alternative nutrient sources for cassava micropropagation. A Low Cost Medium (LCM) whereby the conventional sources of four Murashige and Skoog (MS) macronutrients had been replaced with locally available fertilizers was developed. Stanes Iodized Microfood® from Osho Chemical Industries in Nairobi was used as the alternative source of micronutrients. Modified conventional MS medium was used as the control. Both media were supplemented with 30 g/l of table sugar and 3 g/l of gelrite. Two cassava varieties, Muchericheri and KME 1 were regenerated on the two media. Node, leaf and root formation patterns plus plant height were determined and compared. A reduction of 95.50% in nutrient cost was achieved. The two cassava varieties had a significantly (p < 0.05) higher number of nodes on the conventional medium compared to LCM. There were no differences in node formation by the two varieties on the low cost medium during both initiation and multiplication. KME 1 produced significantly more leaves on the LCM compared to Muchericheri during both initiation and multiplication. Acclimatization of plantlets was successful; hence, this protocol can be adopted in cassava regeneration. Keywords: Tissue culture, cassava, nutrient sources, micropropagation, low cost medium, acclimatization

Potential of Native Rhizobia in Enhancing Nitrogen Fixation and Yields of Climbing Beans (Phaseolus vulgaris L.) in Contrasting Environments of Eastern Kenya

Climbing bean (Phaseolus vulgaris L.) production in Kenya is greatly undermined by low soil fertility, especially in agriculturally prolific areas. The use of effective native rhizobia inoculants to promote nitrogen fixation could be beneficial in climbing bean production. In this study, we carried out greenhouse and field experiments to evaluate symbiotic efficiency, compare the effect of native rhizobia and commercial inoculant on nodulation, growth and yield parameters of mid-altitude climbing bean (MAC 13 and MAC 64) varieties. The greenhouse experiment included nine native rhizobia isolates, a consortium of native isolates, commercial inoculant Biofix, a mixture of native isolates + Biofix, nitrogen treated control and a non-inoculated control. In the field experiments, the treatments included the best effective native rhizobia isolate ELM3, a consortium of native isolates, a commercial inoculant Biofix, a mixture of native isolates + Biofix, and a non-inoculated control. Remarkably, four native rhizobia isolates ELM3, ELM4, ELM5, and ELM8 showed higher symbiotic efficiencies compared to the Biofix. Interestingly, there was no significant difference in symbiotic efficiency between the two climbing bean varieties. Field results demonstrated a significant improvement in nodule dry weight and seed yields of MAC 13 and MAC 64 climbing bean varieties upon rhizobia inoculation when compared to the non-inoculated controls. Inoculation with ELM3 isolate resulted to the highest seed yield of 4,397.75 kg ha−1, indicating 89% increase over non-inoculated control (2,334.81 kg ha−1) and 30% increase over Biofix (3,698.79 kg ha−1). Farm site significantly influenced nodule dry weight and seed yields. This study, therefore, revealed the potential of native rhizobia isolates to enhance delivery of agroecosystem services including nitrogen fixation and bean production. Further characterization and mapping of the native isolates will be imperative in development of effective and affordable commercial inoculants.

Genetic Characterization of Rhizosphere Bacteria that Inhabit Common Bean Nodules in Western Kenya Soils

Background: With the increasing world population, there is increasing demand for food. This has led to overuse of agricultural farms causing reduced soil fertility and accumulation of phytopathogens. Inorganic fertilizers and pesticides have been extensively used in response to these challenges. Extensive integration of inorganic fertilizers and pesticides in the farming system has contributed to soil and water pollution worsening the eutrophication in rivers lake waters. Alternative farming methods are therefore necessary to address this problem. Recent studies have found that rhizobacteria that colonize nodules of leguminous plants are capable of increasing yield and health of the tested plants. Their plant growth promoting ability depends on the rhizobacteria type, soil properties, and climatic conditions. The aim of this study, therefore, was to genetically characterize rhizobacteria that closely associate with common bean nodules by analyzing the nucleotide sequence of 16SrRNA gene. Results: The 16SrRNA gene analysis revealed that common bean nodule associated bacteria in Western Kenya soils are genetically diverse as indicated by the evolutionary genetic distances. Not even organisms in the same species had zero genetic distance though they formed independent groups on the phylogenetic tree. The isolates belonged to the genus Pseudomonas, Providencia, Rhizobia, Klebsiella, Enterobacter, Delfitia and Acinetobacter as identified through nucleotide BLAST at the NCBI GenBank database. Conclusion: Rhizobacteria that colonize common bean nodules are genetically diverse. Those found in this study may be adaptable to Western Kenya soils and further tests are required to determine their plant growth promoting efficiency.

Xerophyta viscosa Aldose Reductase, XvAld1, Enhances Drought Tolerance in Transgenic Sweetpotato

Sweetpotato is a significant crop which is widely cultivated particularly in the developing countries with high and stable yield. However, drought stress is a major limiting factor that antagonistically influences the crop’s productivity. Dehydration stress caused by drought causes aggregation of reactive oxygen species (ROS) in plants, and aldose reductases are first-line safeguards against ROS caused by oxidative stress. In the present study, we generated transgenic sweetpotato plants expressing aldose reductase, XvAld1 isolated from Xerophyta viscosa under the control of a stress-inducible promoter via Agrobacterium-mediated transformation. Our results demonstrated that the transgenic sweetpotato lines displayed significant enhanced tolerance to simulated drought stress and enhanced recuperation after rehydration contrasted with wild-type plants. In addition, the transgenic plants exhibited improved photosynthetic efficiency, higher water content and more proline accumulation under dehydration stress conditions compared with wild-type plants. These results demonstrate that exploiting the XvAld1 gene is not only a compelling and attainable way to improve sweetpotato tolerance to drought stresses without causing any phenotypic imperfections but also a promising gene candidate for more extensive crop improvement.

Effect of nitrogen sources on the yield of common bean (Phaseolus vulgaris) in western Kenya

ABSTRACT Depletion of soil nutrients due to continuous cultivation without adequate external fertilization is one of the challenges facing many smallholder farmers in western Kenya. This study was conducted to assess the effects of organic (water hyacinth compost), inorganic (urea) nitrogen (N) sources, and commercial Rhizobia inoculant on the yield of common bean (Phaseolus vulgaris) for two consecutive seasons in the short rains (2013) and long rains (2014). The experiments were laid out in a randomized complete block design and replicated four times. Triple superphosphate was applied to all treatments except those with compost to ensure that the soil had adequate phosphorus (P). Yellow and Rose coco bean varieties grown with urea and inoculated with commercial Rhizobia inoculant gave significantly higher yield of 382 kg ha−1 and 341 kg ha−1, respectively in the short rains (SR) season. In the long rains (LR) season bean yield was high in water hyacinth compost (1526 kg ha−1) and control with non-limiting P (1300 kg ha−1) treatments. Commercial Rhizobia inoculant did not significantly increase in yield in the SR and LR seasons. There was no significant influence on soil properties after two seasons of continuous cultivation of common bean and application of organic and inorganic fertilizers. These results demonstrate that water hyacinth compost improved bean yield in the LR season. However, longer field testing and economic analysis are required for it to be recommended as a substitute for inorganic N source among smallholder farmers.

Genetic characterization and diversity of Rhizobium isolated from root nodules of mid-altitude climbing bean (Phaseolus vulgaris L.) varieties

The increasing interest in the use of rhizobia as biofertilizers in smallholder agricultural farming systems of the Sub-Saharan Africa has prompted the identification of a large number of tropical rhizobia strains and led to studies on their diversity. Inoculants containing diverse strains of rhizobia have been developed for use as biofertilizers to promote soil fertility and symbiotic nitrogen fixation in legumes. In spite of this success, there is paucity of data on rhizobia diversity and genetic variation associated with the newly released and improved mid-altitude climbing (MAC) bean lines (Phaseolus vulgaris L.). In this study, 41 rhizobia isolates were obtained from the root nodules of MAC 13 and MAC 64 climbing beans grown in upper and lower midland agro-ecological zones of Eastern Kenya. Eastern Kenya was chosen because of its high production potential of diverse common bean cultivars. The rhizobia isolates were characterized phenotypically on the basis of colony morphology, growth and biochemical features. Rhizobia diversity from the different regions of Eastern Kenya was determined based on the amplified ribosomal DNA restriction analysis (ARDRA) of PCR amplified 16S rRNA genes using Msp I, EcoR I, and Hae III restriction enzymes. Notably, native rhizobia isolates were morphologically diverse and grouped into nine different morphotypes. Correspondingly, the analysis of molecular variance based on restriction digestion of 16S rRNA genes showed that the largest proportion of significant (p < 0.05) genetic variation was distributed within the rhizobia population (97.5%) than among rhizobia populations (1.5%) in the four agro-ecological zones. The high degree of morphological and genotypic diversity of rhizobia within Eastern Kenya shows that the region harbors novel rhizobia strains worth exploiting to obtain strains efficient in biological nitrogen fixation with P. vulgaris L. Genetic sequence analysis of the isolates and testing for their symbiotic properties should be carried out to ascertain their identity and functionality in diverse environments.

Determination of Stem Rust Ug99 Disease Severity in Selected Wheat Backcrosses in Kenya

Stem rust (Pucciniagraministritici) is a disease of economic importance in wheat (Triticumaestivum L.) worldwide. The objective of this study was to determine the disease severity of the BC1F1 plants in the nursery at Kenya Agricultural and Livestock Research Organization, Njoro. Kingbird (resistant) was crossed with Njoro Bw2 (susceptible) to obtain F1 plants. The F1plantswere backcrossed with Njoro Bw2 to obtain a BC1F1 progeny. Two hundred and forty seeds of the BC1F1 plants, twenty eight resistant and susceptible parents were planted in two replicates and the Modified Cobb’s Scale was used to record their disease severity scores. An excel work sheet programmed with the AUDPC formula was used to compute the Area Under Disease Progress Curve (AUDPC) values for BC1F1 plants. Variation of the disease severity scores and mean AUDPC among the wheat plants was analysed using Analysis of variance (ANOVA). Results showed 47.9% ofresistant plants that portrayed the pseudo black chaff (PBC) trait had low disease severity mean scores ranging from 0 to 1.0414 with mean AUDPC values below 99.8. The resistant plants without PBC were 43.3 % and had disease severity mean score ranging from 0.9098 to 1.3686 with mean AUDPC values ranging from 99.8 to 260.The BC1F1 plants that showed susceptibility to stem rust disease were 21 (8.8 %) and had the highest disease severity mean score ranging from 1.3223 to 1.4914 with the highest mean AUDPC values ranging from 282.5 to 431.3. The ANOVA computation showed that, variation in the disease severity and in the mean AUDPC values among the individual plants (P < 0.001) was significant, but variation in mean AUDPC values from one replicate to another (P > 0.001) was not significant. The BC1F1 wheat plants showed a low disease severity score in the field indicating that these plants received the APR genes for stem rust and this could be useful for wheat improvement through breeding.