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Abstract A field experiment involving two plant densities (83,333 and 166,666 plants per hectare), two cropping systems (monoculture and mixed culture) and five cowpea (Vigna unguiculata L. Walp.) genotypes (3 farmer-selected varieties: Bensogla, Sanzie and Omondaw, and 2 breeder-improved cultivars: ITH98-46 and TVuI509) was conducted for two years in 2005 and 2006 at Nietvoorbij (33°54S, 18°14E), Stellenbosch, South Africa, to evaluate the effect of these treatments on the growth and symbiotic performance of cowpea. The results showed that, of the five cowpea genotypes, plant growth and N2 fixation were significantly greater in the three farmer-selected varieties (Sanzie, Bensogla and Omondaw) relative to the two improved cultivars (ITH98-46 and TVuI509). Furthermore, plant growth and symbiotic performance (measured as tissue N concentration, plant N content, 15N natural abundance and N-fixed) were significantly (P:50.05) decreased by both high plant density and mixed culture (intercropping). However, the %Ndfa values were significantly (P:S0.05) increased by both high plant density and mixed culture compared to low plant density or monoculture (or monocropping). Whether under low or high plant density, the cv. Sanzie was found to accumulate significantly greater total N per plant in both 2005 and 2006, followed by the other two farmer varieties relative to the improved cultivars. Similarly, the actual amount ofN-fixed was much greater in cv. Sanzie, followed by the other farmer varieties, under both low and high plant density. The data also showed better growth and greater symbiotic N yield in cowpea plants cultivated in monoculture (or low plant density) relative to those in mixed culture (or high plant density). Our data suggest that optimising legume density in cropping systems could potentially increase N2 fixation in cowpea, and significantly contribute to the N economy of agricultural soils in Africa.

Abstract A field experiment involving two plant densities (83,333 and 166,666 plants per hectare), two cropping systems (monoculture and mixed culture) and five cowpea (Vigna unguiculata L. Walp.) genotypes (3 farmer-selected varieties: Bensogla, Sanzie and Omondaw, and 2 breeder-improved cultivars: ITH98-46 and TVuI509) was conducted for two years in 2005 and 2006 at Nietvoorbij (33°54S, 18°14E), Stellenbosch, South Africa, to evaluate the effect of these treatments on the growth and symbiotic performance of cowpea. The results showed that, of the five cowpea genotypes, plant growth and N2 fixation were significantly greater in the three farmer-selected varieties (Sanzie, Bensogla and Omondaw) relative to the two improved cultivars (ITH98-46 and TVuI509). Furthermore, plant growth and symbiotic performance (measured as tissue N concentration, plant N content, 15N natural abundance and N-fixed) were significantly (P:50.05) decreased by both high plant density and mixed culture (intercropping). However, the %Ndfa values were significantly (P:S0.05) increased by both high plant density and mixed culture compared to low plant density or monoculture (or monocropping). Whether under low or high plant density, the cv. Sanzie was found to accumulate significantly greater total N per plant in both 2005 and 2006, followed by the other two farmer varieties relative to the improved cultivars. Similarly, the actual amount ofN-fixed was much greater in cv. Sanzie, followed by the other farmer varieties, under both low and high plant density. The data also showed better growth and greater symbiotic N yield in cowpea plants cultivated in monoculture (or low plant density) relative to those in mixed culture (or high plant density). Our data suggest that optimising legume density in cropping systems could potentially increase N2 fixation in cowpea, and significantly contribute to the N economy of agricultural soils in Africa.

Abstract In 2005 and 2006, 30 and 15 cowpea genotypes were respectively evaluated for plant growth and symbiotic performance at Manga in Northern Ghana, in order to identify Nz-fixing potential of these cowpea genotypes as source of N for cropping systems. The results showed differences in biomass production by the 30 or 15 cowpea genotypes. In 2005, cultivars Fahari, Mchanganyiko, IT97K-499-39, IT93K-2045-29 and IT84S-2246 produced the most shoot biomass, while Apagbaala, Brown Eye, ITH98-46, Vita 7 and Iron Grey produced the least. Of the 15 genotypes tested in 2006, cv. TVu1l424 produced the largest amount of biomass, and ITH98-46, the least. Isotopic analysis of 15N in plant parts also revealed significant differences in 1)15N of the cowpea genotypes studied. As a result, the percent N derived from fixation (% Ndfa) also differed among the cowpea genotypes tested in 2005, with only 5 out of the 30 cultivars obtaining over 50% of their N from symbiotic fixation. Whether expressed as mg Nplant' or kg N.ha-I , the levels of Nz fixation by the cowpea genotypes varied considerably during 2005 and 2006, with values ofN contribution ranging from 14.1 kg N.ha-1 by cv. TVul509 to 157.0 kg N.ha-1by IT84S-2246 in 2005. The amounts ofN-fixed in 2006 ranged from 16.7 kg N.ha-1 by cv. ITH98-46 to 171.2 kg N.ha-1 by TVu11424, clearly indicating genotypic differences in symbiotic N yield. Re-evaluating 15 out of the 30 cowpea genotypes for Nz fixation in 2006, revealed higher % Ndfa values (>50%) in all (15 cowpea genotypes) relative to those tested in 2005, indicating greater dependence on Nz fixation for their N nutrition even though, the actual amounts of fixed-N were lower in 2006. This was due, in part, to reduced plant biomass as a result of very late sampling in 2006, close to physiological maturity (72 DAP in 2006 vs. 46 DAP in 2005) when considerable leaf matter was lost. The amount ofNfixed in 2006 can therefore be considered as being under-estimated.

Human cytomegalovirus (HCMV) is a ubiquitous pathogen with ability to establish a persistent infection in the host for many years. Diseases are more serious in congenitally infected infants and immunocompromised individuals such as AIDS patients and transplant recipients. It rarely causes disease among immunocompetent individuals. The envelope glycoproteins of HCMV (gB, gH, gN, gM, gL and gO) are essential for viral infectivity as they are involved in attachment and penetration of the host cell, cell to cell viral transmission and fusion of infected cells. Also, they are known to be important targets for humoral and cell mediated immune responses against the virus. The hypothesis states that HCMV genotypes are constantly mutating and evolving, then is controlled in a setting of immunocompetence, but in immunocompromised patients, congenitally infected patients or possibly within the CNS, the virus is able to evade the immune system and genotypes may evolve which are more pathogenic and/or neuroinvasive. In current study, a total of 669 CSF samples were collected from Malawian children with neurological illness that have been tested for the presence of HCMV. A comparison study population was also studied which contained 26 HCMV isolates obtained from the Manchester Royal Infirmary Clinical Virology Laboratory. The isolates were originally collected from congenitally CMV infected infants or immunocompromised children and adults showing symptoms of HCMV disease. Positive HCMV samples were screened for glycoproteins (B, H, N, L and O) and then glycotyped by restriction fragment length polymorphisms and sequencing analysis. HCMV DNA was found to be present in 46 (6.7%) out of 669 CSF samples. In 19 of these HCMV positive samples, glycoprotein genotypes (B, H, N, L and O) were identified. The predominant glycoprotein genotypes in the CSF population were as follows, gB type 3(63.2%), gH type 1(73.2%), gN type 4 (50%), gL type 4 (55.8%) and gO type 1 (60%), whilst in the comparison study population (control group) the most common glycoprotein genotypes were; gB type 3 (52.3%), gH type 1 (52%), gN type 4 (60%), gL type 4 (56%) and gO type 1(48%). No statistically significant difference was found between glycoprotein genotypes among the CSF samples and comparison study population. However, when linkage between glycoprotein types was studied and analysed differences between the two populations emerged. The particular glycoprotein linkage (gH1, gN1 and gO1) occured six times in the CSF study population with severe and fatal outcome as it occured four times with fatal outcome, and in two other patients, one was HIV positive and one with sequelae.Novel linkages between gO and gN genotypes were also found (gN3b/gO3), (gN4a/gO4), (gN4b/gO2b), (gN4b/gO3), (gN4d/gO1c), (gN1/gO1c), and (gN4c/gO4). The (gN1/gO1c) combination was occurred three times, but only in CSF study population and was associated with fatal outcomes, two patients died and one was HIV positive patients.RFLP assay was found to have limited efficacy in identification of HCMV genotypes, as discrepancies in genotype results between RFLP and sequencing were found in all glycoprotein genotypes. Thus, sequencing analysis was more accurate and recommended for identification of the HCMV genotypes.In conclusion, investigation of different glycoprotein genotypes in CSF samples has shown no significant correlation between single glycoprotein and disease outcome. Recombination between HCMV strains may lead to progression of disease. However, studying a large group of CSF samples positive for HCMV from immunocompromised patients may clarify the correlation between glycoprotein types and neurological outcome, and lead to improved strategies for treatment and prevention of HCMV associated disease.

The glutathione S-transferase (GST) supergene family encodes isoenzymes that appear to be critical in protection against oxidative stress. Certain GST loci are polymorphic, demonstrating alleles that are null (GSTMI/GSTT1), encode low activity variants (GSTPI), or are associated with variable inducibility (GSTM3). Interleukin-1 (IL- 1) alpha and beta are cytokines involved in recruitment of inflammatory cells, the process of inflammation, and blood-brain barrier breakdown and nerve regeneration. Polymorphisms of both GST and of a complementary interleukin-1 receptor antagonist have been associated with severity and susceptibility to other inflammatory conditions. This thesis examines the influence of the GST and IL-1 genes on both the susceptibility to Multiple Sclerosis (MS), and the course of disease progression. The population examined consisted of four hundred patients with clinically definite MS. Disease severity was measured using the Kurtzke Expanded Disability Status Scale (EDSS), a robust established ranking scale. PCR-based genotyping was performed using DNA extracted from lymphocytes. Significant associations between genotypes and clinical outcome were corrected for known demographic factors influencing prognosis, these being; gender, onset age, and disease duration using the statistical method of logistic regression. Significant associations, withstanding multiple testing corrections, with certain IL-I genotypes and disease severity were found. There was also a significant trend with the GST isoenzymeM 3 that is expressedin nervous tissue. No robust findings suggest that these genes influence susceptibility to MS, but the results suggest that long-term prognosis is genetically influenced by the modulation of inflammatory cytokines and also by the ability to remove the toxic products of oxidative stress.

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