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Record number 355477
Title Ecology and management of charcoal rot (Macrophomina phaseolina) on cowpea in the Sahel
Author(s) Ndiaye, M.
Source Wageningen University. Promotor(en): Ariena van Bruggen, co-promotor(en): Aad Termorshuizen. - [S.l.] : S.n. - ISBN 9789085046646 - 114
Department(s) Biological Farming Systems
PE&RC
Publication type Dissertation, internally prepared
Publication year 2007
Keyword(s) macrophomina phaseolina - vigna unguiculata - vignabonen - plantenziekten - plantenziekteverwekkende schimmels - geïntegreerde plagenbestrijding - teeltsystemen - compost - biologische bestrijding - sahel - niger - macrophomina phaseolina - vigna unguiculata - cowpeas - plant diseases - plant pathogenic fungi - integrated pest management - cropping systems - composts - biological control - sahel - niger
Categories Integrated Control, Integrated Pest Management
Abstract Keywords: Senegal/Niger/rotation/millet/isolate characterization/fonio/compost amendment / bioagent/ Clonostachysrosea /solarization

Cowpea ( Vignaunguiculata Walp.) is the most important pulse crop in theSahelwith nearly 12.5 million hectares per year and is a valuable source of protein for human and animal nutrition. The most limiting factors for crop growth in the Sahelian zone of West Africa are water and nutrient stress. The average cowpea yields in farmers' fields are low (0.2-0.5 ton/ha) and charcoal rot causes on average a yield loss of 10%, which is equivalent to 30.000 tons cowpea - an estimated value of $146 million for Niger and Senegal alone.Disease resistant or tolerant cultivars of cowpea against M . phaseolina are the most efficient control measures but such cultivars are not yet available. Solarization, addition of organic matter, maintenance of high soil moisture, fumigation and use of biocontrol agents have shown to be potential methods for control of soilborne pathogens.The objectives of the thesis is: 1)to characterize cowpea isolates of Macrophomina phaseolina prevalent in the different cowpea cropping systems in Niger and Senegal with respect to culture characteristics and host range; 2) to determine effects of rotation of cowpea with fonio and millet on M. phaseolina disease of cowpea, and production and survival of microsclerotia in soil; 3) to study the effects of compost and a biocontrol agent on M. phaseolina and charcoal rot on cowpea; 4) to study the effects of solarization alone or in combination with organic residues on M. phaseolina and charcoal rot on cowpea.

Macrophominaphaseolina causes heavy yield loss to cowpea ( Vignaunguiculata ) grown in different cropping systems in the Sahel region ofAfrica. It was not known if cropping systems could influence physiological, genetic and pathogenic characteristics of M. phaseolina isolates. This study therefore aimed to analyze the population structure of M . phaseolina associated with three cropping systems in theSahel. Isolates were collected from soil and infected tissues of different cropping systems in Senegal and Niger and their growth potential at different temperatures, their morphology on PDA medium, their virulence on three cowpea cultivars and sequence analysis of the ITS (internal transcribed spacer) region of the nuclear ribosomal DNA gene studied.Isolates of M. phaseolina differed to a limited extent in temperature optimum, genetic make-up, and pathogenicity to cereal crops. The grouping according to physiological and genetic traits did not coincide with that based on pathogenicity. However, for the first time, we showed some specialization in pathogenicity to cereal crops except fonio ( Digitaria exilis )) for isolates obtained from fields grown to millet next to cowpea.

Field observations and invitro studies indicated that fonio is a non-host to M. phaseolina , and millet a poor host, respectively. The influence of continuous cropping of these crops on soil inoculum density of M.phaseolinawas studied under field conditions. The data showed thatfonio was not infected by M. phaseolina , while the root systems of millet had low densities of microsclerotia. Cowpea yielded significantly more hay and pods after 3 years of fonio than after 3 years of millet. We conclude that rotation of cowpea with a gramineous crop may lead to a relatively fast decline of inoculum density. In the case of a high inoculum density, fonio can be grown for three years to reduce M . phaseolina densities in soil.

A field experiment was conducted on the effect of compost on soil inoculum and symptom severity of charcoal rot. The experiment was carried out in naturally infested farmers' fields. The effect of 3 or 6 tons of compost and of 6 tons of compost supplemented with 50 kg NPK fertilizer ha -1 , applied in planting holes, on charcoal rot was assessed for three consecutive years. Besides, the combined effects of 3 tons of compost ha -1 and the biocontrol agent Clonostachysrosea (10 8 CFU's per g compost) on charcoal rot development and cowpea production were investigated. Our results indicated that in Sahelian sandy soil good control and substantial increase of cowpea yield can be achieved by soil amendment with 6 tons of compost ha -1 . An even greater yield increase is achieved by soil amendment with 6 tons of compost and 50 kg NPK ha -1 or 3 tons ha -1 of compost augmented by C.rosea .

The combined effects of soil solarization and amendment with millet residues and paunch contents on the survival of M . phaseolina and development of charcoal rot of cowpea were assessed in a naturally infested soil.In amended plots, solarization increased the soil temperature to 50°C for at least 4 h day -1 during June, leading to a significant reduction of soil inoculum of M . phaseolina by 44%. Paunch amendment (3 tons ha -1 ) caused 66% reduction of initial inoculum in the solar-heated plots while millet amendment did not enhance microsclerotia reduction in solarized plots. These observations demonstrated that under conditions where solarization alone does not provide sufficient control, the combination with organic amendments improves yields and reduces infection by M . phaseolina . High-N containing amendments may be most effective, such as the paunch used in this study. Solarization as well as application and incorporation of millet residues or paunch content in moistened soil can double cowpea production in poor, naturally infested soil of the Sahelian zone and contribute to the management of paunch waste from slaughter houses in big cities.

In conclusion the study indicated that M . phaseolinaisolates from different cropping systems in theSahelvary with respect to virulence and ability to cause infection on crop species and cultivars.For the first time we found isolates of C . rosea in theSahelthat are efficient at controlling M . phaseolina . In addition we showed that including fonio in the rotation scheme of cowpea and millet, adding millet residues or paunch contents with or without solar heating and application of 3 tons ha -1 of compost augmented with C . rosea reduced charcoal rot disease and increased cowpea yield. These methods can be integrated intodifferent combinations according to local conditions for managing charcoal rot.
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