Genetic fingerprinting and phylogenetic diversity of Staphylococcus aureus isolates from Nigeria

Genetic fingerprinting of 18 different isolates of Staphylococcus aureus from Nigeria using random amplified polymorphic DNA (RAPD) was carried out. Ten out of 100 Operon primers showed polymorphism among the isolates tested generating 88 bands, 51 of which were polymorphic with sizes ranging between 200 and 3,000 bp. All the isolates were classified completely into two major groups (Sa-1 and Sa-2) with twelve different subgroups. Sa-1 group originated from human while isolates from plant and animal origins formed the Sa-2 group. The twelve different subgroups suggest adaptation of S. aureus in the different host cells. This indicates possible relationship between host origin and genetic variation among S. aureus isolates. The DNA fingerprint defined for each race of S. aureus could be useful in epidemiological studies, medical diagnosis and the identification of new strains and their origins. (African Journal of Biotechnology: 2003 2(8): 246-250

Smallholder marketed surplus and input use under transactions costs: maize supply and fertilizer demand in Kenya

This paper assessed the effects of transactions costs—relative to price and non-price factors—on smallholder marketed surplus and input use in Kenya. A selectivity model was used that accounts not only for the effects of fixed and variable transactions costs but also for the role of assets, technology, and support services in promoting input use and generating a marketable surplus. Output supply and input demand responses to changes in transactions costs and price and non-price factors were estimated and decomposed into market entry and intensity. The results showed that while transactions costs indeed have significant negative effects on market participation, cost-mitigating innovations—such as group marketing—are also emerging to mitigate the costs of accessing markets. Output price has no effect on output market entry and only provides incentives for increased supply by sellers. On the other hand, both price and non-price factors have significant influence on adoption and intensity of input use. Overall, the findings suggest that policy options are available other than price policies to promote input use and agricultural surplus.Commercialization, Marketed surplus, Fertilizer use, Transactions cost, Kenya, Agricultural and Food Policy, Agricultural Finance, Consumer/Household Economics, Environmental Economics and Policy, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Institutional and Behavioral Economics, International Relations/Trade, Marketing, Productivity Analysis, Research and Development/Tech Change/Emerging Technologies, Research Methods/ Statistical Methods,

Livelihood Strategies of Resource-Poor Farmers in Striga-Infested Areas of Western Kenya.

Striga hermonthica (del) Benth is threatening rural livelihoods in western Kenya where maize is the major food and cash crop. Vulnerability analysis was conducted on a sample of 802 households in eight districts of Nyanza and Western provinces. Farmers perceived Striga as the major cause of poverty and food insecurity. Both household income and child nutrition indicators showed alarming conditions for the majority of households. The coping strategies and informal safety nets were not capable of addressing the vulnerability issue successfully. A logistic regression model of determinants of poverty was estimated to examine the determinants and correlates of poverty. Results revealed certain characteristics of households that were more likely to be poor: poor access to land and farm assets; high dependency ratio; headed by older farmer with low education attainment; no off-farm work, no cash crops; depend on credit; Striga has been on the farm for long, high perceived yield loss to Striga given high dependency on maize for livelihoods; adopt no integrated Striga control options; and live in Bondo and Vihiga districts. The paper concludes with implications for policy to improve the livelihoods of small-scale farmers in the Striga-affected areas of western Kenya. Key words: livelihoods, maize, Striga, Kenya, Logitlivelihoods, maize, Kenya, Striga, logit, Agricultural and Food Policy, Community/Rural/Urban Development, Consumer/Household Economics, Environmental Economics and Policy, Farm Management, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Health Economics and Policy, Land Economics/Use, Marketing, Productivity Analysis, Research and Development/Tech Change/Emerging Technologies,

Yam (Dioscorea ssp.) domestication by the Nago and Fon ethnic groups in Benin

Guinea yams (Dioscorea cayenensis-rotundata complex; D. rotundata Poir. and D. cayenensis Lam.) have been described as resulting from a process of domestication of wild yams of the section Enantiophyllum by African farmers. Although currently practised by few farmers, the process of yam domestication is still on-going in Benin. In order to document the practices used and the indigenous knowledge maintained by Nago and Fon farmers, 27 villages were surveyed. In total, 57 farmers domesticating yam were identified, and 68 yams newly domesticated (or in domestication) were collected. Fon and Nago farmers domesticate yam mainly to widen the genetic basis of the existing diversity or for simple curiosity. Among the three wild yams species (D. abyssinica Hochst. ex Kunth, D. praehensilis Benth. and D. burkilliana J. Miège) used, D. praehensilis is the most important and the most exploited. Tuber of the wild yams are collected either in the bush (most often near the village) or in the forests (far from the village) during hunting. The domestication process consists of bringing into cultivation selected individuals which go through intense vegetative multiplication and selection procedures (over a lengthy but variable period of time) that induce morphological and biochemical changes in the plant mainly at the tuber level. Individuals resulting from these manipulations were found to be, either similar or identical to known landraces or completely new based on both morphological and isozyme analysis. Because it leads to some new cultivars, this process of domestication has potential in yam breeding and appears to be a strategy that could be useful to breeders, while developing a methodology for participatory breeding of yam

Morphological and isozymic diversity of the cultivated yams (Dioscorea cayenensis/Dioscorea rotundata complex) of Cameroon

Using IPGRI's descriptors, 45 accessions of Guinea yams (Dioscorea cayenensis Lam./ Dioscorea rotundata Poir. complex) collected in Cameroon were classified into six cultivar groups based on their morphological similarities. An identification key is proposed for the cultivar groups. Six enzymatic systems (6PGD, PGI, AAT, SKDH, PGM, EST) were also used to assess genetic variation within these cultivated yams. Twenty-eight genotypes were identified within the 45 accessions analysed. The clustering of accessions based on isozyme data is very close to the one obtained using morphological characters

Harnessing modern biotechnology for tropical tuber crop improvement: yam (Dioscorea spp.) molecular breeding

Yams (Dioscorea spp.) constitute a staple food crop for over 100 million people in the humid and subhumid tropics. They are polyploid and vegetatively propagated. The Guinea yams, Dioscorea rotundata and D. cayenensis, are the most important yams in West and Central Africa where they are indigenous, while D. alata (referred to as water yam) is the most widely distributed species globally. The genetics of yams is least understood among the major staple food crops due to several biological constraints and research neglect. Research to unravel the apparent complexity of the yam genome will have far-reaching implications for genetic improvement of this important tuber crop. Some progress has been made in recent years in germplasm characterization and the development of molecular markers for genome analysis. A genetic linkage map based on amplified fragment length polymorphism (AFLP) markers has been constructed for Guinea and water yams. These linkage maps were used to scan the genome for quantitative trait loci (QTL) associated with genes conferring resistance to Yam Mosaic Virus (YMV) in D. rotundata and anthracnose (Colletotrichum gloeosporioides) in D. alata. In addition, candidate random amplified polymorphic DNA (RAPD) markers associated with major genes controlling resistance to YMV and anthracnose have been identified that could be used for selection and pyramiding of YMV and anthracnose resistance genes in yam improvement. Also, molecular markers such as RAPDs, AFLPs, and microsatellites or simple sequence repeats (SSRs) have been developed for yam genome analysis. An initial c-DNA library has been constructed in order to develop expressed sequence tags (ESTs) for gene discovery and as a source of additional molecular markers. This paper will review the advances made, discuss the implications for yam genetic improvement and germplasm conservation, and outline the direction for future research

A comparative assessment of molecular marker assays (AFLP, RAPD and SSR) for white yam (Dioscorea rotundata) germplasm characterisation

Several DNA-based marker systems are available for genetic fingerprinting of plants but information on their relative usefulness for yam germplasm characterisation is lacking. The efficiency of RAPD, AFLP and SSR markers for the assessment of genetic relationships, and for cultivar identification and discrimination among 45 West and Central African white yam cultivars belonging to 22 morphotypes/cultivar groups was investigated. Dendrograms were produced based on band pattern scores using the UPGMA method. Results showed that each of the three techniques could unequivocably identify each cultivar, but that techniques differed in the mean number of profiles generated per primer (or primer pair) per cultivar, referred to as genotype index (GI). The order of merit based on this criterion in this study was AFLPs (GI = 2.56), SSRs (GI = 0.39) and RAPDs (GI = 0.35). Yam genotypes classified in the same cultivar group based on morphology were often genetically different, emphasising the need for molecular fingerprinting in yam germplasm characterisation. AFLPs showed the highest efficiency in detecting polymorphism and revealed genetic relationships that most closely reflected morphological classification

Genomics of yams, a common source of food and medicine in the tropics

Yams (Dioscorea spp., Dioscoreaceae), grown either for their starchy tubers or medicinal properties, are important crops in the tropics and subtropics. Yams broaden the food base and provide food security and income to over 300 million people. They are vegetatively propagated and comprise both diploid and polyploid species. Despite their economic and socio-cultural importance, very little is known about the genetics and genomics of yams due to research neglect and several biological constraints. Consequently, conventional breeding efforts have been severely hampered. Research to unravel the apparent complexity of the yam genome will have far-reaching implications for genetic improvement of this important tuber crop. Nevertheless, progress has been made recently towards understanding Dioscorea phylogeny and phylogenetic relationships within the genus. Also, improved molecular technologies have been developed for genome analysis, including germplasm characterization, cytogenetics, genetic mapping and tagging, and functional genomics. Genetic linkage maps have been constructed for D. rotundata and D. alata, and quantitative trait loci associated with resistance to Yam mosaic virus in D. rotundata and anthracnose (Colletotrichum gloeosporioides) in D. alata have been identified. In addition, candidate random amplified polymorphic DNA markers associated with major genes controlling resistance to Yam mosaic virus and anthracnose have been identified. These markers could be converted to sequencecharacterized amplified regions and used formarker-assisted selection for resistance to diseases. An initial cDNA library has been constructed to develop expressed sequence tags for gene discovery and as a source of additional molecular markers. Genetic engineering offers a powerful tool, complementing conventional breeding approaches, for yam improvement. Methods for yam transformation, including in vitro plant regeneration, gene delivery, selection of transformed tissues, and recovery of transgenic plants have been developed but still need improvements. This chapter reviews advances made in yam molecular marker development for genome analysis, phylogeny, molecular cytogenetics, characterization of genetic diversity, genetic mapping and tagging, and progress in functional genomics