Genetic variability in yam cultivars from the Guinea- Sudan zone of Benin assessed by random amplified polymorphic DNA

Yam (Dioscorea spp.) is an important food and cash crop in the Guinea-Sudan zone of Benin. The genetic diversity of about 70 cultivars of Dioscorea cayenensis/Dioscorea rotundata (Guinea yam) andabout 20 cultivars of Dioscorea alata (water yam) was analysed using random amplified polymorphic DNA (RAPD). The amplified bands revealed high polymorphism. These polymorphic DNA fragmentswere used to construct dendrograms, clustering all accessions into 18 groups: 12 for D. cayenensis/D. rotundata and six for D. alata. The analysis of molecular variance revealed highly significant variationamong species, among groups within species, and among cultivars within groups. The study showed that the genetic diversity changed along a spatial gradient. In general, there was a tendency that mostof the varieties from the north-east and north-west of the zone investigated appeared to be distinctive from the ones of the centre. However, few varieties were distributed randomly and did not reflect anyspecific relation to their zone of collection. The current study suggests that the Guinea-Sudan zone of Benin has a large gene pool of yam varieties. Yam farmers may have played a significant role in theenrichment and the maintenance of the genetic diversity of yam

Genetic variability of cultivated cowpea in Benin assessed by random amplified polymorphic DNA

Characterization of genetic diversity among cultivated cowpea [Vigna unguiculata (L.) Walp.] varieties is important to optimize the use of available genetic resources by farmers, local communities, researchersand breeders. Random amplified polymorphic DNA (RAPD) markers were used to evaluate the genetic diversity in 70 cowpea accessions collected throughout Benin. Nine random primers were screened on24 accessions to assess their ability to reveal polymorphisms in cowpea and four of them were selected for use in characterizing the total sample. A total of 32 amplified bands were generated by the fourprimers. The number of loci detected varied from 5 to 11. RAPD profiles were analysed and amplified polymorphic DNA fragments were used to construct a dendrogram, clustering the accessions into ninegroups at a similarity index of 71% based on the Unweighted Pair-Group Method using Arithmetic Averages. The genetic diversity among the cowpea cultivars investigated was large and the RAPDproved to be a useful technique to characterise it. Based on the molecular variance, the fixation index suggests a large differentiation of cowpea cultivars in Benin

Evaluation de pratiques culturales relatives à la production de semenceaux et tubercules d'igname (Dioscorea rotundata) au Bénin

Cultural practices evaluation for jam seedling and tuber (Dioscorea rotundata) production in Benin. Effects of eight media and three zones of cutting from mother seed yam into minisets were investigated for their performance in basket nursery using a local white yam Dioscorea rotundata, variety Ignidoun. Methods of land preparation (flat and ridge) for seed yam production were combined with above treatments. Influence of seed yam weight associated with two planting patterns (vertical and oblique) on ware yam production were studied using a variety TDr 179. Analysis of data showed that medium made of cow dung only or with 50 % top soil or mixture of equal quantity of compost and top soil favoured miniset sprouting. Oblique pattern of planting seed yam in sandy soil improved ware yam and tuber yields

Evaluation de l\'activité insecticide de deux plantes Hyptis suaveolens (Linn) et Khaya senegalensis (A. Juss) sur les insectes ravageurs du niébé (Vigna unguiculata L. Walp.)/Use of two insecticidial plants for sustainable cowpea (Vigna unguiculata L. Walp.) protection

Une stratégie de protection de la culture de niébé par les biopesticides a été testée avec les extraits aqueux d\'Hyptis suaveolens (Linn.) et de Khaya senegalensis (A. Juss), issus de matériels végétaux conservés pendant un an, trois mois ou un jour à 5°C. Les ravageurs ciblés sont Aphis craccivora Koch, Megalurothrips sjostedti Trybom et les bruches. Au champ, Callosobruchus maculatus Fabricius et son parasitoïde Uscana lariophaga Steffan sont visés. Les biopesticides sont composées de 37,5 kg de matière végétale pilée, le tous dilué dans 375 litres d\'eau appliquée à l\'hectare. Les resultats ont montré que la forme fraîche des feuilles de H. suaveolens s\'est révélée plus efficace sur les pucerons et les thrips. L\'écorce de 3 mois de K. senegalensis a aussi été plus efficace sur les pucerons. Par contre, l\'écorce fraîche ou celle conservée pendant 3 mois présentent les mêmes effets sur les thrips. Les extraits aqueux des deux plantes à l\'exception de l\'écorce fraîche, ont réduit (P=0,05) la ponte chez C. maculatus, et favorisé le parasitisme des oeufs par U. lariophaga. De plus, la vigueur des graines récoltées n\'a pas été affectée (P=0,05). Ces deux plantes peuvent être exploitées pour une production et une protection durables du niébé.Cowpea production and protection that preserve human heath and environment, needs to be assessed on alternative uses of pest control methods that do not only rely on synthetic insecticides. Plant materials, Hyptis suaveolens (Linn.) leaves and Khaya senegalensis (A. Juss) bark stored for one year, three months or one day, were processed in aqueous forms and tested against Aphis craccivora (Koch.), Megalurothrips sjostedti (Trybom.) and Callosobruchus maculatus Fabricius in field. Their effects on egg-laying activity of C. maculatus and its parasitoïd Uscana lariophaga Steffan were evaluated. Results showed that fresh leaves of H. suaveolens were the most effective on aphids and thrips. Three months storage bark powder extract of K. senegalensis also was effective on aphids. Whereas fresh bark extract or that from 3-month stored material showed similar control level on thrips. All stored plant materials involved in the aqueous extracts of both plants, regardless of storage periods and except the fresh bark form of K. senegalensis, reduced significantly (P=5 %) egg laying activity of C. maculatus on pods, and favoured parasitism of U. lariophaga. Plant aqueous extracts did not significantly affect seed vigour. Overall results reveal that sustainable cowpea production and protection could be developed based on these plants. Keywords: Hyptis suaveolens, Khaya senegalensis, niébé, protection durable, ravageurs./Cowpea, Hyptis suaveolens, Khaya senegalensis, pest, sustainable protection.Sciences & Nature Vol. 4 (1) 2007: pp. 17-2

Postharvest agriculture in changing climates: Its importance to African smallholder farmers

Climate change and variability affect not only the field stages and yields of crops, but also what happens to them after harvest. There has been little discussion of the impacts of climate change on postharvest agriculture, and still less on these impacts in developing countries. Many studies have focused on potential crop yield and pre-harvest implications of different climatic projections, but have omitted an analysis of the need and ability to then protect this increasingly valuable harvest as a vital aspect of food security. Postharvest systems will be affected by changes in temperature, rainfall, humidity, extreme events and the natural and human responses to climate change and variability. This study describes typical grain postharvest systems in east and southern Africa and discusses the likely impacts of different climate change trends on postharvest activities, assets and human well-being outcomes. Adaptation opportunities for creating more climate resilient postharvest agricultural systems and associated livelihoods are identified. Many of these adaptation opportunities are already known and understood by postharvest service providers, highlighting the significant challenge of getting postharvest knowledge into use at a larger scale. A discussion is presented on the factors influencing attempts to strengthen the adaptive capacity of postharvest systems, such as its invisibility, its omission from training curricula, innovation system challenges, the policy bias towards pre-harvest agricultural spending, limited understanding of gender and diversity aspects of postharvest roles, and the dominance of maize in the food system. The study recognises the crucial role of postharvest agriculture in helping communities adapt and cope with change