The role of genetic diversity in sustainable agriculture

The depletion of plant biodiversity with the rapid development of agriculture has attracted growing interest in recent years. This paper discusses the evolutionary consequences of monoculture with emphasis on the buffering effects of genetic heterogeneity on disease. The use of host plant resistance and systemic fungicides as disease control measures and their influence on sustainable agriculture are discussed. Three approaches of re-introducing genetic diversity into modern agriculture are indicated. These are composite crosses, multiline varieties, and variety mixtures. It is concluded that the variety mixtures approach holds promise for developing countries where low input cropping systems are practised. Ghana Jnl agric. Sci. Vol.31(2) 1998: 231-24

Cashew production in the northern part of Ghana

No Abstract. Ghana Journal of Agricultural Science No. 1, 2005: 175-17

Strain Selection for Generation of O-Antigen-Based Glycoconjugate Vaccines against Invasive Nontyphoidal <i>Salmonella</i> Disease

<div><p>Nontyphoidal <i>Salmonellae</i>, principally <i>S</i>. Typhimurium and <i>S</i>. Enteritidis, are a major cause of invasive bloodstream infections in sub-Saharan Africa with no vaccine currently available. Conjugation of lipopolysaccharide O-antigen to a carrier protein constitutes a promising vaccination strategy. Here we describe a rational process to select the most appropriate isolates of <i>Salmonella</i> as source of O-antigen for developing a bivalent glycoconjugate vaccine. We screened a library of 30 <i>S</i>. Typhimurium and 21 <i>S</i>. Enteritidis in order to identify the most suitable strains for large scale O-antigen production and generation of conjugate vaccines. Initial screening was based on growth characteristics, safety profile of the isolates, O-antigen production, and O-antigen characteristics in terms of molecular size, O-acetylation and glucosylation level and position, as determined by phenol sulfuric assay, NMR, HPLC-SEC and HPAEC-PAD. Three animal isolates for each serovar were identified and used to synthesize candidate glycoconjugate vaccines, using CRM₁₉₇ as carrier protein. The immunogenicity of these conjugates and the functional activity of the induced antibodies was investigated by ELISA, serum bactericidal assay and flow cytometry. <i>S</i>. Typhimurium O-antigen showed high structural diversity, including O-acetylation of rhamnose in a Malawian invasive strain generating a specific immunodominant epitope. <i>S</i>. Typhimurium conjugates provoked an anti-O-antigen response primarily against the O:5 determinant. O-antigen from <i>S</i>. Enteritidis was structurally more homogeneous than from <i>S</i>. Typhimurium, and no idiosyncratic antibody responses were detected for the <i>S</i>. Enteritidis conjugates. Of the three initially selected isolates, two <i>S</i>. Typhimurium (1418 and 2189) and two <i>S</i>. Enteritidis (502 and 618) strains generated glycoconjugates able to induce high specific antibody levels with high breadth of serovar-specific strain coverage, and were selected for use in vaccine production. The strain selection approach described is potentially applicable to the development of glycoconjugate vaccines against other bacterial pathogens.</p></div