Dansou Kossou

Sustainable soil fertility management in Benin: learning from farmers

The perception of farmers from the Atacora and Save regions of Benin was studied about the causes and consequences of land degradation and corrective actions for sustaining soil fertility. Research methods in this diagnostic study included group discussions, using non-standardized unstructured interviews and participant observations. Farmland degradation leading to declining yields, and land tenure arrangements were identified as the main constraints on the sustainability of agriculture. In both regions the farmers stated that climatic changes (less and more irregular rainfall), run off, erosion, and overexploitation of farmlands caused land degradation. Soil fertility status was assessed on the basis of dicotyledonous weeds, soil texture and colour, and soil fauna (earthworm casting activity). Farmers have adapted their cropping systems to the local environment by developing traditional and new strategies and activities that could contribute to maintain or enhance crop productivity. These strategies include animal manure, inorganic fertilizer, crop rotation, a five-year fallow, extensive cropping systems with cassava or egusi melon, and emigration. Land tenure arrangements between landlords and migrants affect strategies that can be applied to maintain soil fertility. The importance of building mutual trust and the need to experiment with different land tenure arrangements are indicated. A framework for interactive research where knowledge is collectively generated is proposed in order to test the effectiveness and applicability of some of these local innovations not yet well understood by conventional science.

Grounding agricultural research in resource-poor farmers' needs: a comparative analysis of diagnostic studies in Ghana and Benin

Eight researchers from Ghana and Benin, with different backgrounds but all co-operating within the Convergence of Sciences project, conducted diagnostic studies as a first step of their research aimed at developing technologies together with resource-poor farmers. The purpose of including diagnostic studies was to increase the likelihood that the resulting technologies would be grounded in the needs and opportunities of these farmers. To better understand the potential of diagnostic studies for improving the contribution of agricultural research to farmers’ livelihoods, a comparative study was conducted of the diagnostic studies carried out by the eight researchers. This research on agricultural research was participatory in that its results were arrived at in consultation with the eight researchers. The comparison revealed that diagnostic studies identified and established forums of stakeholders, especially of farmers, who were to play key roles in the co-construction of knowledge during the field experimental phase that followed the diagnostic studies. The diagnostic studies gave farmers a say in the design and conduct of the experimental phase which allowed them to influence the research process in the direction of developing and testing technologies that work in their circumstances and that satisfy their needs and priorities. In addition, the diagnostic studies have led to transparent choices with respect to the selection of sites, farmers and experiments. Furthermore, the conditions for negotiation were created. Finally, the diagnostic studies played a crucial role in making the partners within the Convergence of Sciences project aware of the importance of contextual framework conditions in determining the relevance of the project.

Can convergence of agricultural sciences support innovation by resource-poor farmers in Africa? The cases of Benin and Ghana

The article introduces the IJAS special issue on the Convergence of Sciences (CoS) research programme that took place in Benin and Ghana between 2002 and 2006. CoS sought to develop pro-poor pathways of science. Starting initially from the assumption that science impact could be improved by developing farm technologies that are appropriate for the circumstances of resource-poor farmers, the nine researchers soon ran into the very limited windows of opportunity that the farmers face. Improving productivity at the farm level is thwarted by limited access to markets, infrastructure, inputs, credit and services, and by cheap imports. Farmers have no political clout, and agriculture is a source of rent for a host of actors including local and national governments. In these conditions, poverty reduction requires institutional change rather than participatory technology development. All nine researchers tried in their own way to deal with the institutional dimension. This special issue reports on these attempts. The introductory article provides background and context for understanding the institutional issues involved.

Field trials with plant products to protect stored cowpea against insect damage

Plant products were evaluated under field conditions for their efficacy as insecticides against the cowpea beetle, Callosobruchus maculatus, on stored cowpea. Seeds, mixed with finely ground clay and three volatile oils were stored in air-tight jerry-cans and canisters. Pods were treated with leaf powders of two plant species and stored in traditional palm-leaf huts. Beetle damage was evaluated before and after storage. The treatments did not prevent damage, but after treatment with oils, fewer beans showed beetle emergence holes; also, the percentage of uninfested beans and the weight of one litre of beans were each higher than for untreated beans. The percentage of germination of stored beans was highest after treatment with Ocimum basilicum oil. Leaf powder of Momordica charantia was effective against weight loss of stored seeds, whereas Ficus exasperata caused a decrease in both the percentage of infested beans and the number of emerged beetles, and more parasitoids emerged than from untreated beans. Laboratory tests on the effect of the oils on the development of the beetle and on bean germination did not reveal effects of the oils. We compare data obtained from the laboratory and with those obtained in the field.

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) and about 20 cultivars of Dioscorea alata (water yam) was analysed using random amplified polymorphic DNA (RAPD). The amplified bands revealed high polymorphism. These polymorphic DNA fragments were 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 variation among 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 most of 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 any specific 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 the enrichment and the maintenance of the genetic diversity of yam.

Sensibilite des bois de construction des greniers traditionnels aux attaques de Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

RésuméL’étude a portésur l’évaluation de la susceptibilité des diverses espèces de bois impliquées dans la construction des cribs et des greniers aux infestations de Prostephanus truncatus (Horn), grand foreur des grains décelé au Bénin en 1984.A cet effet, une enquête réalisée a permis de recenser et de retenir dix espèces de bois des plus utilisées pour la constitution des échantillons ayant servidans ces essais. Les morceaux de bois après un séchage artificiel sont réduits à une longueur de 20 cm avec des diamètres variant de 2 à 2,6 cm, des teneurs en eau de 11,1 à 12,7% (base humide) et des densités de 0,445 à 0,994 g/cm3. Ils sont infestés par des adultes de P. truncatus âgés de moins de 7 Jours obtenus à l’issue de quatre générations d’insectes maintenus sur des épis de maïs. Deux modes d’infestation (libre et forcée) sont réalisées pour cheque espèces de bois à raison de quatre répétitions par mode. Les écarts de température et d’humidité relative qui ont caractérisé le milieu expérimental sont de 20–35°C et de 60–90% durant les 45 jours d’exécution au-delà desquels divers paramètres ont permis d’apprécier la sensibilité des différentes espèces de bois.La synthèse des résultats portant sur divers paramètres, notamment le nombre d’insectes ayant pénétré les bois, le nombre de larves recensées et les dégâts subis par les diverses espèces de bois, a permis de dégager Elaeis guineensis Jacq. et Holarrhena floribunda (G. Don) comme les espèces les plus résistantes. Les bois les plus sensibles sont Tectona grandis L., Fagara xanthoxyloides Lam., Azadirachta indica A. Juss et Mallotus oppositifolius (Geisel) Mull. Arg.AbstractVarious wood species used for granary or crib construction were tested for their susceptibility to Prostephanus truncatus (Horn), a new stored grain pest in Benin found in 1984. Ten of the widely used wood species were chosen after survey in infested zones. Wood samples were dried in the oven (60°, 72 hr). They were reduced to 20 cm length, with diameter 2.0–2.6 cm and moisture content varying from 11.1–12.7%, respectively. Wood densities ranged from 0.455–0.999 g/cm−3. Fifty adult insects (<7 days old) were released into the middle of a sample made up of the 10 wood species for free-choice assays and 20 insects per wood species in no-choice tests. Four replicates were set up for each category. After 45 days of exposure at a temperature of 20–35°C and 60–90% r.h., data related to number of Insects that had penetrated each wood, number of larvae, and length of tunnelling were assessed. From the overall data analysis, Elaeis guineensis Jacq. and Holarrhena floribunda (G. Don) appeared least susceptible. Tectona grandis L., Fagara xanthoxyloides Lam., Azadirachta indica A. Juss and Mallotus oppositifolius (Geisel). Mull. Arg. were the more susceptible wood species.

Chemical Composition and Insecticidal and Repellent Effect of Essential Oils of Two Premna Species against Sitotroga cerealella

This work aims to study for the first time the chemical composition and evaluate insecticidal and repellent effects of essential oils of Premna angolensis and Premna quadrifolia leaves, against Sitotroga cerealella, an insect pest of rice stocks as alternatives to synthetic pesticides. The GC-MS analysis showed that essential oil of P. angolensis contains 29 compounds representing 96.1% of the oil and 42 compounds corresponding to 91% for the essential oil of P. quadrifolia. The main constituents regardless of the species were β-caryophyllene (13.1%), (E)-β-caryophyllene (13.5%), octen-3-ol (3.2%–28%), phytol (3.7%–4.9%), β-elemene (1.4%–21%), globulol (11.2%), germacrene-D (8.9%), α-humulene (2.9%–6.4%), α-pinene (5%), sabinene (3.7%), δ-cadinene (0.4%–3.3%), and linalool (3.3%). The results of laboratory tests showed that both essential oils have insecticidal and repellent effects on S. cerealella. Presenting the results, the damage caused by the adults and larvae of S. cerealella was evaluated by calculating the percentage of grains attacked and weight loss thereof. The results suggest that volatile extracts of P. angolensis and P. quadrifolia can be used as alternatives to synthetic chemicals in paddy protection against S. cerealella.

Field evaluation of the efficacy of neem oil (Azadirachta indica A. Juss) and Beauveria bassiana (Bals.) Vuill. in cotton production

Neem oil (Azadirachta indica A. Juss) alone and combined with the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (isolate Bb11) was applied to control cotton pests. The efficacy of these treatments was compared with that of synthetic insecticides applied either in a calendar‐based application or in the ‘Lutte Etagée Ciblée’ (LEC) strategy, consisting of using first calendar‐based (half‐dose) applications followed by threshold‐based treatments. The experiment was carried out in collaborative research with farmers in three cotton agro‐ecological zones differing in rainfall, pest prevalence, and farming practices. The neem oil and neem oil‐Bb11 treatments required 2 to 6 applications, while conventional and LEC received 6 to 8 applications. The percentage of damaged reproductive organs in plots treated with neem oil and neem oil plus Bb11 was higher than that recorded under the conventional and LEC strategy, with exception of the zone with the highest rainfall; this resulted in yields being 25% and 39% lower, respectively. Yields in the biopesticide plots were 26–42% higher and in the conventional and LEC plots 44–59% higher than those in the control plots that received only water. Overall, the LEC regime scored best, both in yield and profitability. The incidence of natural enemies was highest in the control and in the plots treated with biopesticides. Although the use of entomopathogen Bb11 and neem oil avoids many problems associated with the application of synthetic insecticides, their efficacy needs to be enhanced by improved formulation or by combining them with other pesticides.

Field evaluation of the synergistic effects of neem oil with Beauveria bassiana (Hypocreales: Clavicipitaceae) and Bacillus thuringiensis var. kurstaki (Bacillales: Bacillaceae)

In the present study, the synergistic effects of Beauveria bassiana (Bals.-Criv. Vuill.) (isolate Bb11) and Bacillus thuringiensis var. kurstaki (Berliner) with neem oil were evaluated in three agroecological zones in Bénin. Four bioinsecticide treatments (neem oil, neem oil and B. bassiana used separately for different target pests, neem oil mixed with B. bassiana and neem oil mixed with B. thuringiensis) were compared with a calendar-based treatment using synthetic insecticides and a control without insecticides. The bioinsecticide treatments were less effective than the calendar-based treatment at controlling cotton pests. There was no difference in yields and the number of damaged bolls in plots under treatments with the four bioinsecticide formulations, suggesting an absence of synergy between neem oil and B. bassiana and neem oil and B. thuringiensis. The numbers of natural enemies in all the bioinsecticide treatment plots and the control plots were similar and higher than those in the calendar-based treatment plots. The highest yield and profitability were obtained with the calendar-based treatment. Screening the compatibility of plant-based products and biopesticides through bioassays is essential for a successful application of their combinations in any integrated pest management strategy.

Ovicide and Larvicide Activities of the Essential Oils Extracted from Polyalthia longifolia and Clausena anisata on Sitotroga cerealella

This work has objectives to study the chemical composition of volatile extracts obtained from leaves of Polyalthia longifolia and Clausena anisata and to evaluate their ovicide and larvicide effects by fumigation against Sitotroga cerealella, as alternative to the pesticides of synthesis. The analyses of the extracts by GC-MS showed that the essential oil of P. longifolia contains 57 compounds representing 86.1% of oil and 26 compounds corresponding to 97.3% of the essential oil of C. anisata. The main compounds identified for the extract of P. longifolia are the β-Caryophyllene (24.5%), Allo-Aromadendrene (13.5%), the α-Zingiberene (9.4%), the α-Humulene (8.5%) and the α-Selinene (2.6%). The extract of C. anisata mainly composed of methyl chavicol (69.9%) is characterized by the presence of oxygenated monoterpens (1.4%), hydrogenated monoterpens (7.8%), hydrogenated sesquiterpens (16.2%), oxygenated sesquiterpens (1.7%) and of aromatic compounds (69.9%). The biological test results showed that the treatments by fumigation done with the essential oils reduce meaningfully (p<0.001) the bursting of the ovums on the paddy rice. The essential oil of C. anisata has completely inhibited the viability of the larvas and the emergence of adult butterflies from the dose 0.5 µl mL-1 contrary to P. longifolia that recorded respectively 10.0±0.3% and 50.0±0.2% at the strong dose 3 µl mL-1. The study has, otherwise, shown that the essential oils delayed the cycle of development “ovums to adult” of S. cerealella (29.0±0.4 to 35.4±0.5 days) in relation to the witness (25±0.1 days). The essential oil of C. anisata proved to be more poisonous for the juvenile stages of S. cerealella. These results provide the scientific basis for potential alternatives to the synthetic fumigants in subsistence and commercial agriculture.