Mutualism between euryhaline tilapia Sarotherodon melanotheron heudelotii and Chlorella sp.—Implications for nano-algal production in warmwater phytoplankton-based recirculating systems

The West-African euryhaline tilapia, Sarotherodon melanotheron heudelotii shift from visually feeding on zooplankton when juveniles to mostly filter feeding on phytoplankton when adults. When reared using an appropriate ration in intensive aquaculture systems, S. m. heudelotii also consume algal-based detritus, and contribute to sediment mineralization, clean up their environment, and ultimately stimulate and sustain algal growth. We analysed such practical advantages for phytoplankton-based recirculating systems, using S. m. heudelotii and Chlorella sp. as biological material originating from the prototype of such a system operated in Senegal. We performed a 24-h factorial design experiment in 36 tubs, cross-classifying three levels of S. m. heudelotii (fishless control, unfed fish, and fed fish) with four levels of Chlorella initial density.Chlorella overall mean density increased significantly from fishless, to unfed fish, and fed fish treatments, and with Chlorella initial density. S. m. heudelotii did not alter nitrogen nor phosphorus concentrations, only affected by algal initial densities. Most ammonia excreted by fish was probably uptaken by Chlorella. Bacteria-mediated diurnal nitrification was possibly an alternative ammonium loss mechanism at highest oxygen concentrations. Algae were not limited by nitrogen or phosphorus but most likely by low dissolved organic carbon availability. Chlorella differential responses with fed vs. unfed Sarotherodon suggest that CO₂ supplied by heterotrophic S. m. heudelotii respiration played a key role. Observed Chlorella growth rates were similar to the highest rates obtained in algal mass cultures, enriched with CO₂, nitrate and phosphate, under artificial lighting.Our results suggest the existence of a Sarotherodon-Chlorella mutualism in our systems, where S. m. heudelotii provide CO₂, the major limiting factor of Chlorella growth, whereas Chlorella oxygenate and detoxify the water media from ammonia, promoting S. m. heudelotii production. This mutualism could be used to optimize photosynthetic suspended-growth aquaculture systems, particularly in the Tropics where light is abundant and temperature is continuously high.     

Combined effect of ascorbic acid and gamma irradiation on microbial and sensorial characteristics of beef patties during refrigerated storage

The present study was undertaken to evaluate the effect of ascorbic acid concentrations (0.03 to 0.5%) and irradiation doses (0.5 to 4 kGy) on microbial growth, color coordinates (L, a, and b), and sensory characteristics (taste and odor) of beef patties during storage at 4 +/- 1 degrees C. Ascorbic acid was also compared to citric acid at a similar pH value in order to differentiate the effects of ascorbic acid from those of pH reduction. Results showed significant reduction (p< or = 0.05) of aerobic plate counts (APCs) and total coliforms, and a significant interaction (p< or = 0.05) between ascorbic acid and irradiation dose was observed. The irradiation treatment had detrimental effects on redness, yellowness, and hue angle values of meat. However, incorporation of ascorbic acid into the meat before irradiation resulted in significant (p< or = 0.05) stabilization of color parameters. The color improvement obtained with ascorbic acid was not related to the pH reduction. Also, no significant detrimental effect on taste or odor was found in irradiated samples containing ascorbic acid.     

Effect of native and allochthonous arbuscular mycorrhizal fungi on Casuarina equisetifolia growth and its root bacterial community

Exotic trees are often planted to recover degraded lands. Inoculation with mycorrhizal fungi can improve their survival. Plant growth is partly dependent on the strain used, but little attention has been paid to the selection of mycorrhizal fungi. The aim of this study was to determine whether the growth of Casuarina equisetifolia L. (Johnson) is affected by two different mycorrhizal inocula generated using fungal spores retrieved from an Australian site (allochthonous soil) and a Senegalese site (native soil) under C. equisetifolia trees. Comparative experiments were conducted with plants in a Senegalese soil, previously sterilized or not, and grown in a greenhouse. At harvest, parameters related to plant growth and mycorrhization were evaluated and soil bacterial communities were compared. Tree growth was significantly influenced by both types of inoculants. In unsterilized soil, plants inoculated with the native inoculant were taller than plants inoculated with the allochthonous inoculant and control plants. The frequency of mycorrhization with both inoculants was higher in unsterilized soil. The strongest effects of the mycorhizosphere on the soil microbiome were obtained with the allochthonous inoculum, and analysis of the taxonomic composition revealed mycorrhizal communities specific to each inoculum. These results suggest that the development of C. equisetifolia and its root bacterial community are dependent on the composition of the mycorrhizal inoculum. The functional consequences of this rhizosphere effect in terms of soil fertility should be further studied to better guide reforestation operations.     

Quality control of the vaccines and cold chain during the national vaccination campaigns]

During the two vaccination campaigns against rinderpest and contagious bovine pleuropneumonia (CBPP) in 1989 and 1990, 507 vaccine samples were collected for quality control at each step of the distribution chain from the Veterinary Pharmacy of Abidjan to the vaccinator on the field. Parallel to that, the quality of the cold chain was checked. A total of 463 titrations were performed. All the titration levels were above the OIE/FAO standards, i.e. 10(2.5) DICT50/ml for rinderpest Valence and 10(7) viable germs/ml for contagious bovine pleuropneumonia Valence.     

Ploughing frequency and compost application effects on soil infiltrability in a cotton–maize (Gossypium hirsutum–Zea mays L.) rotation system on a Ferric Luvisol and a Ferric Lixisol in Burkina Faso

One of the key issues to increase soil productivity in the Sahel is to ensure water infiltration and storage in the soil. We hypothesised that reducing tillage from annual to biennial ploughing and the use of organic matter, like compost, would better sustain soil hydraulic properties. The study had the objective to propose sustainable soil fertility management techniques in the cotton–maize cropping systems. The effects of reduced tillage (RT) and annual ploughing (AP) combined with compost application (Co) on soil infiltration parameters were assessed on two soil types. Topsoil mean saturated hydraulic conductivities (K_s) were between 9 and 48 mm h⁻¹ in the Luvisol, while in the Lixisol they were between 18 and 275 mm h⁻¹. In the two soil types compost additions with reduced tillage or with annual ploughing had the largest effect on K_s. Soil hydraulic behaviour was in reasonable agreement with soil pore size distribution (mean values varied from 19.5 to 237 μm) modified by tillage frequency and organo-mineral fertilization. Already the first 3 years of this study showed that use of organic matter, improved soil infiltration characteristics when annual ploughing was used. Also biennial ploughing showed promising results and may be a useful strategy for smallholders to manage these soils.     

Local perceptions and regional climate trends on the Central Plateau of Burkina Faso

Due to devastating droughts in the 1970s and 1980s, climatic and environmental change in the West African Sahel has attracted a great deal of scientific research. While many of these studies documented a long‐term trend of declining rainfall, analyses conducted in the last few years suggest that a ‘recovery’ is underway. Drawing on ethnographic interviews, focus groups, and participant observation in two Provinces of the Central Plateau of Burkina Faso, we elicited local perspectives on these rainfall trends from the people who are most directly affected, namely local farmers. Fieldwork revealed that farmers in the research sites perceive that both overall seasonal rainfall and the number of ‘big rains’ during the rainy season have decreased over the last 30 years. We then tested these perceptions against rainfall records from nearby meteorological stations and found them to be corroborated. This paper illustrates how farmers of the Central Plateau now view drought as ‘normal’, having incorporated drought‐mitigation adaptations into their agricultural systems. Our case study highlights the need for ground truthing scientific analyses and assessing livelihood implications at the local level. It also advocates for sustained institutional support for rural communities, to increase their ability to adapt to climate change. Copyright © 2008 John Wiley & Sons, Ltd.     

Sorghum-cowpea Intercropping: An Effective Technique Against Runoff and Soil Erosion in the Sahel (Saria,Burkina Faso)

In the Central Plateau of Burkina Faso, runoff on bare soil amounts to 40% of annual rainfall and soil losses reach 4 to 8 Mg ha-¹ a-¹, despite slopes of under 3%. Several studies have shown that mulching the soil surface can reduce runoff by over 60%. However, the scarcity of straw and the incompatibility of mulching with mechanical soil preparation have prevented the large-scale adoption of the technique. The study conducted in Saria village where annual rainfall is 800 mm,set out to evaluate the efficacy of sorghum-cowpea intercropping in reducing runoff and erosion. The study design comprised five plots set up so as to recover runoff and transported solids, on a Ferric lixisol with a slope of 0.7%. Three years results showed that sorghum-cowpea intercropping reduces runoff by 20-30% compared to a sorghum monoculture and by 45-55% compared to a cowpea monoculture. Soil loss is also reduced with intercropping by at least a half compared to sorghumand cowpea monoculture. Moreover, it transpired that sorghum-cowpea intercropping is also beneficial in agricultural production terms, since the grain yield of the intercropped plots was double that obtained with sorghumor cowpea monocultures. The better crop production can be an asset for the widespread use of this technique in the country. An evaluation of the advantages of the legume in terms of nitrogen supplies to the cereal (N 2 symbiotic fixation) and of added soil OM will be useful in improving the cost-effectiveness of such a technique.     

Diversity,distribution and prevalence of vegetable-infecting geminiviruses in Burkina Faso

In West and Central Africa, as in many regions of the world, vegetables are severely affected by geminivirus diseases. In Burkina Faso, observation of various virus-like symptoms, especially on tomato, suggests the involvement of several geminiviruses and underlines the pressing need for additional information on their diversity, distribution, prevalence and host plant reservoirs. Large-scale surveys conducted in Burkina Faso confirmed the presence of tomato (yellow) leaf curl diseases (ToLCD-TYLCD) and geminiviruses in all localities with mean prevalences of 25% and 45%, respectively. Five geminiviruses including four begomoviruses (pepper yellow vein Mali virus (PepYVMLV), tomato leaf curl Burkina Faso virus, tomato leaf curl Mali virus and tomato leaf curl Ghana virus) and a dicot-infecting mastrevirus (chickpea chlorotic dwarf virus) were characterized on tomato. In addition, PepYVMLV and cotton leaf curl Gezira virus (CLCuGeV) were characterized on pepper and okra, respectively, in combination or not with alphasatellites and betasatellites for CLCuGeV. The most severe, prevalent and widely distributed virus on vegetables was PepYVMLV, which was characterized for the first time in combination with a genetically divergent DNA-B component that may constitute a key factor of PepYVMLV pathogenicity. Of the eight weeds identified as potential reservoir hosts of begomoviruses, four host PepYVMLV. The results confirm the importance of geminivirus diseases on vegetable crops in Burkina Faso and highlight the complex association of geminiviruses and satellites. The detection of begomoviruses in weeds growing close to crops points to the increasing necessity to consider reservoir plants and virus communities in the control of virus diseases.     

Rapid Screening of Cacao Genotypes for Field Resistance to Phytophthora palmivora Using Leaves, Twigs and Roots

Black pod, caused by Phytophthora spp. is one of the most important diseases of cacao occurring worldwide. Losses due to black pod caused by P. palmivora are still moderate in Côte d'Ivoire but P. megakarya causes high losses in Ghana and other Central African countries. Variation in field attack has been observed between cacao genotypes, but evaluation of pod losses is unsuitable for obtaining rapid progress in breeding. Results of inoculation tests using young detached leaves, twigs and roots, obtained from field and nursery plants, are presented here and compared to field resistance of similar genotypes observed over a 10-year period. Nine different Upper Amazon Forastero genotypes were tested together with progenies obtained by crossing these with the susceptible check IFC5 (Amelonado genotype). Rank correlations between the early screening tests and the level of field attack were positive and mostly significant (r=0.58–0.95). The coefficient of correlation was slightly higher for leaves (r=0.88) and roots (r=0.89) than for twigs (r=0.76). Also, resistance of the different plant organs was correlated (r=0.6–0.9). Resistance of the Upper Amazon parents was well correlated with the resistance of their cross progenies (r=0.7–0.9), suggesting that resistance is highly heritable. Resistance of leaves and twigs from the nursery was better correlated with field resistance than resistance of leaves and twigs from the field, which might result from more uniform growing conditions in the nursery. Inoculation of leaves appears the most suitable early screening method for black pod resistance. Application of this test in breeding more resistant cacao cultivars is discussed.