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Kimiti J.M.,South Eastern Kenya University
African Journal of Agricultural Research | Year: 2011

The effect of integrated soil fertility management (ISFM) on root growth of selected cowpea varieties in two sites with contrasting rainfall amounts over two seasons was investigated. Nine cowpea varieties were used as test crop and the treatments applied include a control, farmyard manure at 2.5 t ha -1,triplesuperphosphate (TSP) at 15 kg ha -1 as (P2O5, 0:46:0), and TSP mixed with farmyard manure at the singly applied rates. The experiment was laid down as a split plot design and it was replicated three times. Data collected include root and shoot biomass at 50% flowering, and shoot biomass at crop maturity. In addition, root to shoot ratios at 50%, correlations between root biomass and shoot biomass at 50% flowering, and correlations between root biomass at 50% flowering and shoot biomass at crop maturity were also determined. The data were analysed as a split plot design using GenStat for Microsoft windows. Results obtained revealed that addition of nutrient inputs enhanced root biomass at Ndunguni during both the long and short rains and only in two treatments at Kavuthu during the short rains. However, addition of nutrients relatively lowered root: shoot ratios in most treatments in both study sites during the two seasons indicating phosphorus (P) deficiency in the study sites. Furthermore, strong positive and significant (p < 0.05) correlations between root and shoot iomass were recorded during the long rain season which was relatively dry compared to the short rain season, indicating the dependence of shoot growth on root growth under limiting moisture conditions. These results revealed the need to add nutrients, especially P, to enhance cowpea root growth and the importance of moisture in root and shoot growth in the drylands. © 2011 Academic Journals. Source

Kavembe G.D.,University of Konstanz | Kavembe G.D.,South Eastern Kenya University | Kautt A.F.,University of Konstanz | Machado-Schiaffino G.,University of Konstanz | Meyer A.,University of Konstanz
Molecular Ecology | Year: 2016

Ecological diversification through divergent selection is thought to be a major force during the process of adaptive radiations. However, the large sizes and complexity of most radiations such as those of the cichlids in the African Great Lakes make it impossible to infer the exact evolutionary history of any population divergence event. The genus Alcolapia, a small cichlid lineage endemic to Lakes Magadi and Natron in East Africa, exhibits phenotypes similar to some of those found in cichlids of the radiations of the African Great Lakes. The simplicity within Alcolapia makes it an excellent model system to investigate ecological diversification and speciation. We used an integrated approach including population genomics based on RAD-seq data, geometric morphometrics and stable isotope analyses to investigate the eco-morphological diversification of tilapia in Lake Magadi and its satellite lake Little Magadi. Additionally, we reconstructed the demographic history of the species using coalescent simulations based on the joint site frequency spectrum. The population in Little Magadi has a characteristically upturned mouth - possibly an adaptation to feeding on prey from the water surface. Eco-morphological differences between populations within Lake Magadi are more subtle, but are consistent with known ecological differences between its lagoons such as high concentrations of nitrogen attributable to extensive guano deposits in Rest of Magadi relative to Fish Springs Lagoon. All populations diverged simultaneously only about 1100 generations ago. Differences in levels of gene flow between populations and the effective population sizes have likely resulted in the inferred heterogeneous patterns of genome-wide differentiation. © 2015 John Wiley & Sons Ltd. Source

Gikuma-Njuru P.,University of Waterloo | Gikuma-Njuru P.,South Eastern Kenya University | Hecky R.E.,University of Minnesota | Guildford S.J.,University of Minnesota | Macintyre S.,University of California at Santa Barbara
Limnology and Oceanography | Year: 2013

Measurements of nutrient concentrations and physicochemical parameters were carried out monthly between March 2005 and March 2006 along a transect between the Nyanza Gulf and the open waters of Lake Victoria to evaluate spatial and seasonal variations in nutrient fluxes and ecosystem metabolism. Nutrient concentration gradients were observed between the deep and seasonally stratifying main lake basin and the large, shallow riverinfluenced Nyanza Gulf, which are connected by the relatively deep and narrow Rusinga Channel. Nutrient gradients were steepest in the Rusinga Channel where there was always a strong gradient in electrical conductivity. A mixing-box model used to quantify nutrient fluxes and ecosystem metabolism along the gulf and the channel showed that nutrients entering the gulf through river inflows and municipal sources were largely retained in the gulf, with only a small fraction transferred into the main lake. In contrast, the main lake was a net exporter of dissolved inorganic phosphorus to the gulf (110 mg P m-2 yr-1), which is in contrast to the paradigm that the gulf is a major contributor to the increasing nutrient enrichment and, hence, eutrophication of the greater Lake Victoria. The channel had net regeneration of dissolved nutrients indicating net heterotrophy; whereas in the gulf, there was net consumption of dissolved nutrients, resulting in high estimates of net ecosystem production (570 mg C m-2 yr-1) and, hence, net autotrophy. Nitrogen balance ranged from +3 to +15 mg N m-2 yr-1, indicating dominance of nitrogen fixation over denitrification in both the gulf and the channel, which are both well-oxygenated. Source

Makau C.M.,University of Nairobi | Towett P.K.,University of Nairobi | Abelson K.S.P.,Copenhagen University | Kanui T.I.,South Eastern Kenya University
Brain and Behavior | Year: 2014

Background: The role of noradrenergic system in the control of nociception is documented in some vertebrate animals. However, there are no data showing the role of this system on nociception in the marsh terrapins. Methodology: In this study, the antinociceptive action of intrathecal administration of the α2-adrenoreceptor agonist clonidine and α2-adrenoreceptor antagonist yohimbine was evaluated in the African marsh terrapin using the formalin test. The interaction of clonidine and yohimbine was also evaluated. Results: Intrathecal administration of clonidine (37.5 or 65 μg/kg) caused a significant reduction in the mean time spent in pain-related behavior. Yohimbine, at a dose of 25 μg/kg, significantly blocked the effect of clonidine (65 μg/kg). However, administration of yohimbine (40 or 53 μg/kg) caused a significant reduction in the mean time spent in pain-related behavior. Intrathecal administration of yohimbine (53 μg/kg) followed immediately by intrathecal injection of the serotonergic methysergide maleate (20 μg/kg) resulted in a significant reversal of the antinociceptive effect of yohimbine. Conclusion: The present study documented the intrathecal administration of drugs in the marsh terrapin, a technique that can be applied in future studies on these animals. The data also suggest the involvement of both α2-adrenoreceptors and 5HT receptors in the modulation of nociception in testudines. © 2014 The Authors. Brain and Behavior published by Wiley Periodicals, Inc. Source

Kimatu J.N.,South Eastern Kenya University
Journal of Tropical Forest Science | Year: 2011

Grevillea robusta is a widely grown agroforestry tree and is regarded as a pioneering coloniser of disturbed sites. Our current understanding on changes of species due to disturbance, abiotic conditions and biotic interactions is very minimal. We investigated a leaf-spotting disease and abnormal growths on G. robusta in Yala and Kodera forest plots in Nyanza province, Kenya. The study comprised symptomology, identification of causal pathogens as well as tissue and soil analyses. Phyllosticta spp. and Pestalotia spp. fungi were isolated from the leaf spots. Seedling reinoculation confirmed Phyllosticta spp. as the lesser opportunistic cause of the leaf spot. However, mineral and proteoid root analyses suggested that abiotic and genetic factors were the main causes of the leaf spotting. The Yala forest had lower pH, phosphorus toxicity (> 0.07%) and poor water drainage, while the Kodera forest had generally high manganese toxicities in soil and leaf tissue. Source

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