The effects of maize planting density and weeding regimes on light and water use

Light and water are among essential resources required for production of photosynthates in plants. A study on the effects of weeding regimes and maize planting density on light and water use was conducted during the 2001/2 short and 2002 long rain seasons at Muguga in - the central highlands of Kenya. Weeding regimes were: weed free (W1), weedy (W2), herbicide (W3) and hand weeding twice (W4). Maize planting densities were 9 (D1) and 18 plants m-2 (D2) intercropped with Phaseolus vulgaris (beans). The experiment was laid as randomized complete block design replicated four times and repeated twice. All plots were thinned to 4 plants m-2 at tasseling stage (96 DAE) and thinnings quantified as forage. Soil moisture content (SMC), photosynthetically active radiation (PAR) interception, evapo-transpiration (ET crop), water use efficiency (WUE), and harvest index (HI), were determined. Percent PAR was higher in D2 than in D1 before thinning but higher in D1 than in D2 after thinning in both seasons. PAR interception was highest in W2 but similar in W1, W3 and W4 in both seasons. SMC was significantly lower in W2 but similar in W1, W3 and W4. D2 had lower SMC than D1 in season two. Weeding regime significantly influenced ET crop, while planting density and weeding regime significantly influenced WUE and HI. D2 maximizes water and light use for forage production but results to increased intra-specific plant competition for water and light severely before thinning (96 DAE) that reduce grain yield in dual purpose maize, relative to D1

Influence of Cyclophosphamide on the Haematological Profile of Laboratory Bred African Soft-furred Rats (Mastomys natalensis)

The African soft-furred rat (Mastomys natalensis) has been shown to be a possible model for propagation  of Trypanosoma brucei gambiense. This study aimed at determining the baseline biological reference values  and reproductive data of a laboratory bred Mastomys colony, which was established at TRC. In addition,  the effect of cyclophosphamide (an immunosuppressant) treatment (s) on the haematological profile  was investigated. The mean gestation period was 23 days and the mean litter size was eight. At birth, the  pups weighed 2.4±0.23 g and the weights increased to 78.0±10.6 g in males and 53.9±4.5 g in females by  90 days. The mean haematological values were significantly (p<0.05) higher in adults than juveniles.  However, there was no statistical difference of haematological values between the sexes.  Cyclophosphamide treatment caused a macrocytic hypochromic anaemia, which was noted 24 hours after  treatment and was more severe in animals treated more than once. Thus, in studies involving a disease that  causes anaemia, repeated cyclophosphamide treatment should be limited. Our study is a contribution to  the clinical and biological characterization of the disease pattern in this preferred rodent model of T. b.  gambiense.

Hysteresis of Backflow Imprinted in Collimated Jets

We report two different types of backflow from jets by performing 2D special relativistic hydrodynamical simulations. One is anti-parallel and quasi-straight to the main jet (quasi-straight backflow), and the other is bent path of the backflow (bent backflow). We find that the former appears when the head advance speed is comparable to or higher than the local sound speed at the hotspot while the latter appears when the head advance speed is slower than the sound speed bat the hotspot. Bent backflow collides with the unshocked jet and laterally squeezes the jet. At the same time, a pair of new oblique shocks are formed at the tip of the jet and new bent fast backflows are generated via these oblique shocks. The hysteresis of backflow collisions is thus imprinted in the jet as a node and anti-node structure. This process also promotes broadening of the jet cross sectional area and it also causes a decrease in the head advance velocity. This hydrodynamic process may be tested by observations of compact young jets.Comment: 9 pages, 5 figures, accepted for publication in ApJ

Mixed QCD and weak corrections to top quark pair production at hadron colliders

The order $\alpha_s^2 \alpha$ mixed QCD and weak corrections to top quark pair production by quark antiquark annihilation are computed, keeping the full dependence on the $t$ and $\bar t$ spins. We determine the contributions to the cross section and to single and double top spin asymmetries at the parton level. These results are necessary ingredients for precise standard model predictions of top quark observables, in particular of top spin-induced parity-violating angular correlations and asymmetries at hadron colliders.Comment: 12 pages, 9 figure

Genetic diversity of Kenyan Prosopis populations based on random amplified polymorphic DNA markers

Several Prosopis species and provenances were introduced in Kenya, either as a single event or repeatedly. To date, naturally established Prosopis populations are described as pure species depending on site, despite the aforementioned introduction of several species within some sites. To determine whether naturally established stands consist of a single or mixture of species, six populations from Bamburi, Bura, Isiolo, Marigat, Taveta and Turkwel were compared for relatedness with reference to Prosopis chilensis, Prosopis juliflora and Prosopis pallida using random amplified polymorphic DNA markers. Cluster analysis based on Nei’s genetic distance clustered Kenyan populations as follows: Marigat, Bura and Isiolo with P. juliflora, Bamburi with P. pallida and Taveta with P. chilensis, whereas the Turkwel population is likely to be a hybrid between P. chileneis and P. juliflora. Four populations had private markers, revealing germplasm uniqueness. Expected heterozygosity tended to be larger for Kenyan populations (ranging from 0.091 to 0.191) than in the three reference (ranging from 0.065 to 0.144). For the six Kenyan populations and two P. juliflora provenances from the Middle East, molecular variation was larger within populations than between population. Higher molecular variance among populations is attributed to their geographical separation and the low variation within populations is due to gene flow between individuals within a population. Overall, this study shows that (1) the Kenyan Prosopis populations are genetically isolated, (2) multiple introductions enhanced genetic diversity within sites and (3) P. juliflora and its hybrid are the most aggressive invaders.Key words: Prosopis chilensis, Prosopis juliflora, Prosopis pallida, multiple introductions, genetic diversity

ANTIINFLAMMATORY PROPERTIES OF DICHLOROMETHANE: METHANOLIC LEAF EXTRACTS OF CAESALPINIA VOLKENSII AND MAYTENUS OBSCURA IN ANIMAL MODELS

Objective: Inflammation is the reaction to injury of the living tissues. Conventional medication of inflammation is expensive and arguably associated with various severe adverse effects hence the need to develop herbal agents that are effective as alternative. Caesalpinia volkensii and Maytenus obscura are plants that grow in Mbeere County of Eastern region of Kenya. This study was designed to evaluate the anti-inflammatory activity of C. volkensii and M. obscura plants. Methods: Experimental animals were divided in to four groups; normal group, diseased negative control group, diseased reference group and diseased experimental groups. Inflammation was inducted into the mice using carrageenan. The experimental groups were treated with leaf extracts of the plants at concentration of 50 mg/kg, 100 mg/kg and 150 mg/kg. Anti-inflammatory activities in rats were compared with diclofenac (15 mg/kg) as the standard conventional drug. Results: The leaf extracts of C. volkensii reduced the paw edema by between 6.50%-13.42% while the extracts of M. obscura reduced it by between 4.94%-22.36%. Diclofenac reduced the paw edema by between 4.11%-10.47%. Conclusion: The phytochemical screening results showed that the extracts of C. volkensii had flavonoids, steroids and phenolics while the leaf extracts M. obscura had phenolics, terpenoids and saponins. Flavonoids, saponins and phenolics have been associated with anti-inflammatory activities. Therefore, the study has established that the DCM: methanolic leaf extracts of Caesalpinia volkensii and Maytenus obscura are effective in management of inflammation

Plant Parasitic Nematodes Associated With Coffee in Kenya and Factors Influencing their Occurrence, Abundance and Diversity

Frequent detection of galls on coffee roots has raised concerns of nematodes in coffee production systems in Kenya. This study aimed at determining the occurrence of nematodes associated with coffee in Kenya and the role of crop management, cultivars, soil properties and agro ecological zones on the abundance and frequency of nematodes. A survey was conducted in the prime coffee growing areas in 10 counties namely; Machakos, Makueni, Kiambu, Embu, Kirinyanga, Nyeri, Meru, Kisii, Nandi and Trans-Nzoia. Nematodes were extracted using a combination of centrifugal floatation and Modified Baermann techniques and identified to genera level.  Nutrient analysis was carried out using the Double Mehlich method. Results showed that nematodes belonging to 30 genera were recovered from coffee agro-ecosystems. Plant parasitic nematodes were the most prevalent with 64% frequency (19 genera) of occurrence followed by bacterial feeders at 24%. The genus Tylenchulus, Meloidogyne and Pratylenchus were the most dominant across all the coffee growing areas. Coffee farms in the coffee-tea zones (Upper Midland 1) harbored the highest numbers of plant parasitic nematodes, followed by Upper Midland 2 and least in the marginal coffee growing zones (Upper Midland 3). Well managed farms had less plant parasitic nematodes compared to neglected farms. K and P significantly contributed to the variation in the nematode community composition. This study demonstrated the prevalence of plant parasitic nematodes, factors that influence their abundance and distribution and justifies need for further management of nematodes in coffee production. Key words: Abundance, agro-ecologial zones, diversity, nematode genera, nutrient

Reaction of Selected Coffee Germplasm to Root-Knot Nematodes in Kenya

Coffee is one of the most important cash crops in Kenya and a leading export earner. Nematodes are among the most important biotic constraint in coffee production in Kenya and crop improvement work has mainly been breeding for resistance to diseases such as coffee berry disease and coffee leaf rust. However resistance has been used successfully in other coffee producing countries and it is one of the most economical and practical nematode management strategies. A greenhouse study was conducted to test the response of local and exotic coffee germplasm to root knot nematodes (RKNs). Ten (10) cultivars provided by Coffee Research Foundation (CRF) were tested for resistance to Meloidogyne incognita under greenhouse conditions (25±2oC). Nematodes were extracted from the roots using Modified Baermann Technique and enumerated using Cobbs slide. After 90 days of plant growth, the disease severity was evaluated and the experiment repeated twice. Galling indices (GI), egg mass indices (EMI) and nematode populations recovered from soil samples indicated a range of responses from resistant to highly susceptible.  Three breeder’s lines including Robusta tree 1, Robusta tree 2 and Robusta tree 3 were rated resistant with galling indices of 1.2-3.0. This study has demonstrated the potential of host resistance as a strategy in the management of nematodes in coffee for increased productivity. Field evaluation needs to be conducted to confirm these findings. The identified resistance sources can be utilized to deploy resistance genes to improve existing varieties that have high commercial value but lack resistance to nematodes.   Key words: Resistance, susceptible, galling indices, nematode population, cultivar

Risk factors of virologic failure and slow response to art among HIV-infected children and adolescents in Nairobi

Background: Antiretroviral therapy (ART) in resource-limited settings is effective when backed up with adequate clinical, immunological, and virologic monitoring. Undetected, virologic failure results in increased HIV-1 drug resistance mutations (DRMs), morbidity and mortality, or the need for costly second-line and third-line ART.Objective: To evaluate the prevalence, patterns, and risk factors of virologic failure and slow response to ART, among children and adolescents in resource-limited settings in Nairobi, Kenya.Design: A Retrospective study.Setting: The 8 Lea Toto Programme (LTP) Clinics in Dagoretti, Dandora, Kangemi, Kariobangi, Kawangware, Kibera, Mukuru, and Zimmerman areas of Nairobi. Subjects: One hundred and forty-six HIV-infected children and adolescents aged 1 month to 19 years of the LTP in Nairobi Kenya. Medical and demographic data including, HIV-1 viral loads, information on adherence to ART, HIV-1 DRMs and other key determinants of virologic failure, collected over a period of 2 years, was used for this study.Results: A threshold of 1,000 HIV RNA copies/ml was used to determine treatment outcome. The virologic failure rates in this cohort were 43.8% after 6 months, 32.2% after 12 months, 28.8% after 18 months, and 24.0% after 24 months of first-line ART. Twelve (8.2%) of 146 children showed a slow response to ART: they initially failed ART at 12 months, but had treatment success after 18 to 24 months. The rates of virologic rebound were 4 (2.7%) after 18 months and 3 (2.1%) after 24 months of ART. Multivariate Cox proportional hazards regression revealed that children with suboptimal adherence to ART were 37 times more likely to experience virologic failure (P = 0.000003).Conclusions: This study showed that ART implementation in resource-limited settings is effective when regular virologic monitoring, adherence counselling, and HIV-DR testing are available. Secondly, adherence to ART is a strong predictor of treatment outcome for children and adolescents in resourcelimited settings. Therefore, methods of optimizing adherence levels should be explored and implemented