Browsing by Author "Koskey, Gilbert"

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    Agrobiodiversity conservation enhances food security in subsistence‑based farming systems of Eastern Kenya
    (BioMed Central, 2016) Mburu, Simon Wambui; Koskey, Gilbert; Kimiti, Jacinta Malia; Ombori, Omwoyo; Maingi, John M.; Njeru, Ezekiel Mugendi
    Background: Globally, there is great concern about expanding agricultural activities due to their impact in the conservation of agrobiodiversity. African continent is known for its richness in biodiversity. In Kenya, there is a continuous unabated expansion of agriculture into natural habitats due to demographic and economic pressures posing a significant threat to biodiversity. Therefore, there is a need to study biodiversity loss and its regain through practices in agricultural landscapes. In this study, we assessed the status of agrobiodiversity and its contribution to food security in four agroecological zones of Eastern Kenya. Sixty households were sampled from two selected agroecological zones (upper and lower midland zones) in Embu and Tharaka-Nithi counties. Structured questionnaires and checklists were used to collect the data. Results: Thirty-nine crop species were identified dominated by vegetables, fruits, legumes and cereals with relative densities of 28.8, 20.5, 18.3 and 8.3 %, respectively. Embu Lower Midland and Tharaka-Nithi Lower Midland zones had relatively higher crop species richness of 243 and 240, respectively, and Shannon–Wiener diversity indices (H′) of 3.403 and 3.377, respectively, compared with Embu Upper Midland and Tharaka-Nithi Upper Midland zones with species richness of 229 and 207, respectively, and H′ of 3.298 and 3.204, respectively. Conclusions: Households from lower midland zones with high crop diversity and richness were more food secure compared with those from the Upper Midland zones with low crop diversity and richness. These findings suggest that farm production systems with high agrobiodiversity contributed more toward food security among smallholder farmers in the selected sites. Keywords: Agrobiodiversity, Food security, Biodiversity loss, Smallholder farmers, Kenya
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    Differential Response of Promiscuous Soybean to Local Diversity of Indigenous and Commercial Bradyrhizobium Inoculation under Contrasting Agroclimatic Sones
    (Springer Nature, 2020) Mburu, Simon Wambui; Koskey, Gilbert; Njeru, Ezekiel Mugendi; Ombori, Omwoyo; Maingi, John M.; Kimiti, Jacinta Malia
    Promiscuous soybeans are grain legumes that nodulate with diverse strains of indigenous Bradyrhizobium and play a significant role in biological nitrogen fixation through symbiosis. However, experiments on the potential use of promiscuous soybean varieties have recorded very low nodulation and poor nitrogen fixation probably due to ineffective native Bradyrhizobium isolates. Experiments were designed to investigate symbiotic nitrogen fixation of two promiscuous soybean varieties (SB8 and SB126) with indigenous Bradyrhizobium isolates in contrasting agroclimatic zones through greenhouse and field experiments. Inoculation of soybeans in the greenhouse had a significant (p < 0.001) effect on shoot and nodule dry weight. The best performing indigenous isolates RI9 and RI4 from the greenhouse study outperformed the commercial inoculant (Biofix) in symbiotic effectiveness with 119.17%, 142.35% and 101.01%, respectively. Inoculation in the field experiments showed a significant (p < 0.0001) increase in shoot dry weight and grain yield of promiscuous soybean. Agroclimatic zones showed significant (p < 0.0001) variability in above ground biomass of soybean due to inoculation. Despite the apparent promiscuity of the soybean varieties used, the response in nodulation suggests the cultivars grown under contrasting agroclimatic zones have a preference to specific Bradyrhizobium isolates.
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    Leveraging the Complex Interplay between Arbuscular Mycorrhizal Fungi, Seasonal Dynamics, and Genotypic Diversity to Optimize Maize Productivity in Semi-Arid Agroecosystems
    (Heliyon, 2024-09) Kipkorir, Koech; Koskey, Gilbert; Njeru, Ezekiel Mugendi; Maingi, John
    Maize production under low-input agricultural systems in semi-arid areas of Sub-Saharan Africa faces significant challenges, primarily stemming from the synergistic impacts of climate vari ability and suboptimal agronomic practices. Harnessing soil microbiota, particularly arbuscular mycorrhizal fungi (AMF), represents a pivotal strategy for bolstering low-input systems. However, their functional utility is contingent upon their compatibility with the prevailing environmental conditions and biotic interactions. This study examines the influence of two distinct AMF in oculants on the growth and yield attributes of diverse maize genotypes across varying seasons within semi-arid regions of Kenya. We hypothesized that AMF inoculants exhibit differential adaptability to varying environmental sites and seasons, and their interaction will enhance the provision of key ecosystem services important for maize production. Field experiments were conducted in three semi-arid Counties (Tharaka-Nithi, Embu, and Kitui) during the 2019/2020 cropping seasons. A randomized complete block design with three replications and three treat ments was adopted. Treatments consisted of Rhizatech (a commercial AMF inoculant), a con sortium of AMF isolates (Rhizophagus irregularis and Funneliformis mosseae), and a non-inoculated control. In season one, notable interaction effects were observed for both site × maize genotype (p = 0.0007) and site × AMF inoculation (p < 0.0001), whereby Duma 43 genotype had the highest yield in Embu (11.93 t ha− 1 ) and Kitui (11.76 t ha− 1 ) counties, and Rhizatech and con sortium inoculation consistently led to elevated grain yields across all three genotypes in Kitui, surpassing non-inoculated controls. AMF inoculation notably augmented phosphorus (P) uptake, with Rhizatech demonstrating a 79.7 % increase and consortium showing a 38.7 % increase in shoot P content compared to control plants in season 1. These findings highlight the complex interplay between AMF effectiveness, seasonal variations, and maize diversity. Further research is needed to elucidate the underlying mechanisms driving these seasonal shifts, allowing for opti mized AMF inoculation strategies for improved maize performance under diverse conditions.
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    Potential of Native Rhizobia in Enhancing Nitrogen Fixation and Yields of Climbing Beans (Phaseolus vulgaris L.) in Contrasting Environments of Eastern Kenya
    (Frontiers Media, 2017) Koskey, Gilbert; Mburu, Simon W.; Njeru, Ezekiel M.; Kimiti, Jacinta M.; Ombori, Omwoyo; Maingi, John M.
    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.
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    Symbiotic efficiency and diversity of native rhizobia isolated from climbing beans (phaseolus vulgaris l.) in Embu and Tharaka Nithi Counties, Kenya
    (Kenyatta University, 2016-11) Koskey, Gilbert
    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.
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    Symbiotic efficiency and diversity of native rhizobia isolated from climbing beans (phaseolus vulgaris l.) in Embu and Tharaka Nithi Counties, Kenya
    (2016-11) Koskey, Gilbert
    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 mid-altitude 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 of PCR 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-1) compared to the Biofix-CIAT 899 (76.13 plant-1) and non-inoculated control plants (52.08 plant-1). 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-CIAT 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.