An historical review of progress to control key cowpea biotic constraints in Burkina Faso

273Proceedings of the Fifth World Cowpea Conference

An historical review of progress to control key cowpea biotic constraints in Burkina Faso

B.C. Dabiré1*, J.B. Tignegré1, N.M. Ba1, M. Tamò2, A. Sanon1, T.J. Ouédraogo1,

B.J. Neya1, N. Muleba2, W. Hammond2, and O. Coulibaly2

1Institut de l’Environnement et de Recherches Agricoles, 04 BP 8645, Ouagadougou 04, Burkina Faso2IITA-Benin, 08 BP 0932, Tri Postal, Cotonou, Benin*Corresponding Author: [email protected]

AbstractCowpea farming practices have been ongoing for millennia and have always faced various challenges including diseases, insects, and weeds, that lower its yield to no more than 200 kg/ha. This economically and nutritionally important crop has been a major research focus of the International Institute of Tropical Agriculture (IITA) and of several national agricultural research systems (NARS) in sub-Saharan Africa (SSA) and partner universities. Researchers have begun to develop sustainable solutions that will minimize WKH�XVH�RI�V\QWKHWLF�SHVWLFLGHV� IRU�SURWHFWLQJ� WKH�FURS� LQ� WKH�¿HOG�DQG�VHHGV� LQ�VWRUDJH��5HVHDUFK� DFWLYLWLHV� RI� HQWRPRORJLVWV� KDYH� PDGH� LGHQWL¿FDWLRQ� RI� SHVWV� SRVVLEOH� ZKLOH�also ensuring better understanding about their biology and ecology and plant damaging relationships. Through joint efforts by IITA, NARS, universities, and advanced research LQVWLWXWLRQV�� DQG� WKH� VXSSRUW� IURP�¿QDQFLDO� SDUWQHUV� YLD� UHVHDUFK�QHWZRUNV�� UHVHDUFKHUV�were able to develop a wide range of improved varieties that tolerate yield limiting biotic stresses. Progress has been made in the protection of cowpea from the initial stages when application of synthetic insecticides was promoted through reduced frequency and targeted insecticide sprays to the deployment of natural enemies of the most economically important insect pests. The concept of integrated pest management has become a reality in sustainable cowpea production. The cowpea lines resulting from selections made among local farmers’ varieties under no insecticide application in Burkina Faso have reduced the need for pesticide application. Combined with application of insecticidal plant extracts, these selected lines can attain up to 600 kg/ha. Finally, it is now possible to store cowpea VHHGV�ZLWKRXW� FKHPLFDOV� E\� XVLQJ� WULSOH� EDJJLQJ�ZKLFK� VWLÀHV� EUXFKLGV� �ZHHYLOV�� RI� DLU��Prospects include exploiting the possibilities of biological control and, at the same time, using advanced technological opportunities offered by biotechnology to control cowpea SHVWV�DQG�PLQLPL]H�ORVVHV�LQ�WKH�¿HOG�DQG�LQ�VWRUDJH��

Introduction At this period of celebrations of the 50th anniversaries of independence in several West African countries, a food crisis sparking the revolt of the hungry is still a reality. Certainly one of the most obvious answers to this potential food crisis should be the development and use of locally available crops, such as cowpea. In fact, some governments in West Africa are already promoting the improved production, local consumption, and marketing of cowpea. The article by Assane Soumano from Niger in the daily newspaper Sahel appeared on 9 July 2010 and is an illustration of this strong commitment. It states “it is not known how or why, but it is clear that, in recent years, the pot of cowpea has replaced youngsters’ teapot. The delicious cowpea dish, this local good food, is available.”

274 Innovative research along the cowpea value chain

The promotion of cowpea production and safe storage practices constitutes one of the pillars of the strategy for improving food security and nutrition of the poor, including small-scale farmers, the majority of who are women, while contributing to agricultural GLYHUVL¿FDWLRQ��DQG�LQFUHDVHG�SURGXFWLYLW\�DQG�LQFRPH��3URGXFWV�SURFHVVHG�IURP�FRZSHD�grains are nutritious and healthy, and substantially contribute to improving mother and child health, one of the objectives of the Millennium Development Goals (MDGs).

Biotic constraints to the productivity of cowpea in West Africa include in decreasing order of importance: insect pests, fungal, viral and bacterial diseases, and parasitic weeds (Rachie and Roberts 1974, Raheja and Hayes 1975; Muleba et al. 1997). These constraints result in grain yields rarely exceeding 200 kg/ha under traditional farming conditions in Burkina Faso as well as throughout West Africa (Mortimore et al. 1997). The yield potential of cowpea is estimated around 2500 to 3000 kg/ha grains (Raheja 1978), and yields of 1000 to 2000 kg/ha have been obtained with monocultures of improved, drought-resistant cultivars, under minimal insecticide protection (Muleba et al.1991).

During the past 40 years, the International Institute of Tropical Agriculture (IITA) and West African National Agricultural Research Systems (NARS) have partnered with American and African universities in studying the major biotic constraints, and developing sustainable solutions to address them. A historical review of these efforts is presented in this paper for Burkina Faso from 1977 to date.

Major biotic constrains of cowpea productionInsect pests ,Q� %XUNLQD� )DVR�� VHYHUDO� LQVHFW� VSHFLHV� DWWDFN� FRZSHDV� LQ� WKH� ¿HOG� WKURXJKRXW� WKH�growing season, of which aphids, Aphis craccivora Koch (Homoptera, Aphididae), thrips, Megalurothrips sjostedti (Trybom) (Thysanoptera, Thripidae), pod borers Maruca vitrata (Fabricius) (Lepidoptera, Crambidae), and a complex of pod sucking bugs dominated by Clavigralla tomentosicollis Stäl (Heteroptera, Coreidae) are the most economically important. Baseline studies of insects attacking cowpea in the different agroecological zones (Dabiré and Suh 1988) have revealed that in the Sahelian zone, thrips are the most damaging pests. In the Sudano-Sahelian zone the most important species are aphids, thrips, and pod sucking bugs, while aphids, pod borers, and pod sucking bugs abound in the South-Sudanian zone.

Aphid outbreaks in cowpea farms are favored by drought spells (Dabiré 1990). Catches using yellow pans placed at three sites in the three agroclimatic zones of Burkina Faso KDYH�LQGLFDWHG�WKDW�WKH�À\LQJ�DFWLYLW\�RI�A. craccivora starts earlier and is more intensive in the South-Sudanian zone, followed by the central zone, in the Sudano-Sahelian climate. $SKLG�ÀLJKWV�DUH�OHVV�LQWHQVLYH�LQ�WKH�QRUWK��6DKHOLDQ�]RQH��GHSHQGLQJ�RQ�WKH�SUHYDLOLQJ�north-south wind direction (Dabiré 1990)./HJXPH�ÀRZHU�WKULSV�DUH�RQH�RI�WKH�PDMRU�FRQVWUDLQWV�LQ�WKH�&HQWUDO�DQG�(DVWHUQ�UHJLRQV�

of Burkina Faso, often causing WRWDO�\LHOG� ORVVHV�GXH�WR�ÀRZHU�EXG�DQG�ÀRZHU�VKHGGLQJ�(Dabiré and Suh 1988).

After thrips, pod sucking bugs are the second most important cowpea pest group in %XUNLQD�)DVR��ZLWK�D�SHDN�SRSXODWLRQ�OHYHO�DW�SRG�¿OOLQJ�VWDJH��3RG�VXFNLQJ�EXJV�LQFOXGH�the families of Pentatomidae (with Nezara viridula Linnaeus as the most prominent species) and Coreidae: Anoplocnemis curvipes, Riptortus dentipes, Mirperus jaculus, Crinocerus


sanctus, and several species of Clavigralla. In Burkina Faso, C. tomentosicollis is the main cowpea pod sucking bug species constituting 77 to 92% of the collected specimens. Bio-ecological studies of C. tomentosicollis have shown that this insect can easily adapt to the Sahelian environment being able to complete its life cycle at 40 °C and to thrive in a dry environment (Dabiré et al. 2005a) moving from one host plant to another to ensure its survival during the dry season. A total of 24 herbaceous plants, primarily of the Fabaceae IDPLO\��KDYH�EHHQ�LGHQWL¿HG�DV�DOWHUQDWLYH�KRVWV�RI�C. tomentosicollis (Dabiré et al. 2005b). 7KH�PRVW�VLJQL¿FDQW�KRVW�SODQWV��KRVWLQJ�DOO�VWDJHV�RI�LQVHFW�GHYHORSPHQW�DUH�Cajanus cajan (L.) and three species of Rhynchosia: R. memnonia (Del.), R. minima, and R. orthobothrya. The cowpea development stage most favorable to the development of the bug is the “pod ¿OOLQJ´�SHULRG�LQ�FRPSDULVRQ�WR�\RXQJ�GHYHORSLQJ�DQG�PDWXUH�SRGV��'DELUp�HW�DO��F��,W�also appears that chemicals such as the trypsines and cyanogenic glycosides present in mature pods are antinutritional factors detrimental to the development of C. tomentosicollis nymphs (Dabiré et al. 2005c).

In the Sahelian and Sudano-Sahelian zones, the legume pod borer M. vitrata is only present during the rainy season when cowpea is cropped. However, in the South-Sudanian zone M. vitrata can be observed throughout the year as the insect has been reported surviving on wild legumes in the dry season (Ba et al. 2009). During the cowpea cropping season, M. vitrata migrates from the South-Sudanian zone to the rest of the country (Ba et al. 2009).

During storage, cowpea grains are attacked by coleopteran bruchids. Studies in different DJURHFRORJLFDO� ]RQHV� LQ� %XUNLQD� )DVR� KDYH� LGHQWL¿HG�Bruchidius atrolineatus Pic. and Callosobruchus maculatus Fab. (Coleoptera: Bruchidae) as the main stored cowpea grain pests (Ouédraogo et al. 1991; Sanon et al. 1998). The females of both species colonize FURSV�IURP�ÀRZHULQJ�DQG�OD\�WKHLU�HJJV��UHVSHFWLYHO\��RQ�WKH�JUHHQ�DQG�ULSHQLQJ�SRGV��$W�harvest, less than 5% of the seeds from these pods contain bruchid larvae (Sanon et al. 2005). Because of the reproductive diapause induced as a result of climatic conditions prevailing at the beginning of seed storage, only two generations of B. atrolineatus can be observed. In contrast, C. maculatus shows a greater potential of adaptation to the conditions of storage, develops without interruption, and completely replaces B. atrolineatus thanks to its imaginal polymorphism. This is determined by climatic factors, the relative humidity of the air in particular, associated with thermoperiodical variations (Ouédraogo et al. 1991).

Measures to control cowpea pests in Burkina FasoThe overall philosophy underlying the strategy for the protection of cowpea is sustainable integrated pest management (IPM), with particular emphasis on the use of alternatives to highly toxic chemicals. This integrated pest control, while contributing to the protection of the environment and the value-chain stakeholders, aims at reducing production costs and PLQLPL]LQJ�FURS�ORVVHV�LQ�WKH�¿HOG�DQG�GXULQJ�SRVWKDUYHVW�VWRUDJH��&RQWURO�RI�FRZSHD�LQVHFW�SHVWV�LQ�WKH�¿HOG�LQYROYHV�PDQ\�VWUDWHJLHV�

Cowpea intercropped with cereals The most commonly used method to minimize damage from insects on cowpea crops among farmers remains undoubtedly intercropping: the association of cowpea with sorghum or millet is a widespread cropping method in West Africa. Although farmers do not practice this farming technique intentionally for plant protection reasons, the study of WKH�V\VWHP�VXJJHVWHG�D�EHQH¿FLDO�HIIHFW�LQ�VLJQL¿FDQWO\�UHGXFLQJ�WKH�SRSXODWLRQV�RI�VRPH�


insect pests (Jackai and Adalla 1997). Subsequent studies by Dabire (2001) demonstrated a reduction of cowpea pod sucking bug populations in agro-ecosystems in which cowpea with millet and sorghum are associated.

Chemical controlThe protection of cowpea by using synthetic insecticides remains the most widely practiced control method against cowpea pests although the chemicals are not always accessible and affordable to small-scale farmers in Burkina Faso. Spraying of chemicals has nevertheless become a common practice among groups of producers in relation to increased cultivated areas and the evolution of the status of cowpea as a cash crop in the West African subregion.

In the early days of cowpea research (e.g., the SAFGRAD project), high yielding cowpea varieties were promoted together with the use of chemical insecticides. To obtain the full potential of these varieties such as KN1 (VITA 7), up to seven pesticide applications per cowpea crop cycle were required. As a result, this combination was not easily adopted by the majority of producers. Hence, the need to reduce the number of sprays became an issue for scientists, paving the way for the “minimal spray application” which reduced the number of sprays from seven to two. This minimum application was carried out in conjunction with the determination of the critical phenological stages when the insect attack ZDV�FRQVLGHUHG�WR�EH�GHWULPHQWDO�WR�WKH�SURGXFWLRQ�RI�FRZSHD��WKH�GHYHORSPHQW�RI�ÀRUDO�RUJDQV�DWWDFNHG�E\�WKULSV�DQG�SRGV�GHVWUR\HG�E\�EXJV��,Q�%XUNLQD�)DVR��ZH�KDYH�GH¿QHG�insecticide treatment needs according to the agroecological zones. Thus, for the northern area (Sahel with annual rainfall of between 200 and 400 mm), least infested with cowpea pests, the protection of the crop can be assured by spraying a mixture of Deltamethrin and Dimethoate (1: l/ha of each product) against thrips only once during the season. In the moister Sudanian zone further south (rainfall 800��PP��D�¿UVW�LQVHFWLFLGH�WUHDWPHQW�against pod sucking bugs is essential. Given the continuous production of pods by plants, it is however necessary to make more than one insecticide treatment. In the northern Sudanian zone located in the center of the country (400–800 mm of rainfall), because of the high insect pest pressure, a minimum of two insecticidal treatments must be applied in order to obtain 800�1200 kg/ha grain yield.,QVHFWLFLGH� WUHDWPHQWV� EDVHG� RQ� SRSXODWLRQ� ÀXFWXDWLRQ� DQG� HFRQRPLF� WKUHVKROG�

have replaced systematic applications (Afun et al. 1991). Yields of 1500 to 2000 kg/ha, UHSUHVHQWLQJ��WR��RI�WKH�SRWHQWLDO�\LHOG�RI�FRZSHD�GH¿QHG�E\�5DKHMD��FDQ�EH�obtained with only two spraying of pyrethroids (Dabiré and Suh 1988). The most effective insecticides tested in Burkina Faso include Lambda-cyhalothrin (Karate), Cypermethrin (Cypercal), Permethrin (Percal), and Deltamethrin (Decis), all of them are recommended in association with Dimethoate.

The protection of cowpea by botanical biopesticides The search for alternatives to synthetic chemical control that ensure a safer environment and human health has gained importance during the periods of activity of PEDUNE and PRONAF projects from 1994 to date. Many studies have focused on the use of plant extracts, including those from neem and papaya leaves, for the protection of cowpea in the ¿HOG��([WUDFWV�IURP�QHHP�OHDYHV�DQG�VHHGV�KDYH�VKRZHG�IHHGLQJ�GHWHUUHQW�HIIHFWV�


and growth inhibition towards several insects (e.g., Tanzubil 1991). However, the results obtained have not been consistent, and this has been the major challenge to their adoption as alternatives to chemical insecticides. In Burkina Faso, the application of different neem-based extracts has succeeded to substantially reduce the pressure of insect pests in the ¿HOG��EXW�WKHLU�HIIHFW�LV�PRUH�SURQRXQFHG�LQ�FRZSHD�VHHGV�LQ�VWRUDJH�IDFLOLWLHV��UHODWLYHO\�FORVHG�VWUXFWXUHV��LQ�FRPSDULVRQ�WR�¿HOG�FURSV��,Q�ODERUDWRU\�WHVWV��H[SRVLQJ�WKH�GLIIHUHQW�developmental stages of the bug C. tomentosicollis to high doses of raw and pure extracts from Cassia nigricans, Cymbopogon schoenanthus, and Cleome viscosa can cause total mortality (Dabiré 2001; Ba et al. 2009b). Also, seeds of cowpea plants treated with neem extracts have higher germination (Dabiré 2001).

Host plant resistance 7KH� ¿UVW� VWHS� LQ� WKLV� PHWKRGRORJ\� FRQVLVWHG� LQ� FURVVLQJ� ORFDO� HFRW\SHV� DQG� VHOHFWLQJ�productive varieties without insecticide treatment. The most spectacular breakthroughs using this approach in Burkina Faso were obtained from 1987 onwards, in correspondence with the establishment of RENACO (West and Central Africa Cowpea Network). In collaboration with IITA, the coordinator of the network, the national program of Burkina Faso took the initiative of changing the research strategy. Two basic principles were adopted: plant selection under no or minimum insecticide applications on the one hand, and integration of resistance genes from the available local cultivars on the other hand. Indeed, local varieties have evolved in the hands of farmers for several millennia, without insecticide sprays, having time to adapt to pests. The overall objective of this selection approach without insecticides and crossing with local ecotypes was to develop varieties requiring less pesticide applications. The sources of resistance to the different biotic stresses are given in Table 1, while the varieties obtained so far are summarized in Table 2. This approach has yielded nine varieties less susceptible to thrips attacks, and six aphid resistant/tolerant varieties.

A small number of cultivars have moderate resistance to the pod borer M. vitrata and the pod sucking bug C. tomentosicollis. A local cultivar from Kaokin, a village near Kamboinse LQ�WKH�6XGDQLDQ�]RQH��KDV�EHHQ�LGHQWL¿HG�DV�EHLQJ�OHVV�DWWDFNHG�E\�WKH�SRG�ERUHU��6HYHUDO�ORFDO�FXOWLYDUV�DQG�DQ�LPSURYHG�EUHHGLQJ�OLQH�,7��'��KDYH�EHHQ�LGHQWL¿HG�

with a good potential for tolerance to C. tomentosicollis in Burkina Faso (Dabiré et al. 2010). These varieties were crossed with the best lines already disseminated to farmers in order to incorporate insect tolerance. These new crosses can yield up to 800 kg/ha if treated with neem kernel extracts, demonstrating good prospects for the integrated control of this key cowpea pest in the central region of Burkina Faso (Ba et al. 2009b).

Among the varieties selected without insecticide treatment, yields estimated at 750 kg/ha were obtained with the “Moussa Local”, KVX 414-22-2, KVX404-8-1, KVX414-22-72, KVX 428-9, KVX 404 - 2J, and IT85D-3516 (Table 2).


Table 1. Sources of resistance or tolerance to insects and parasitic weeds.

Bruchids Aphids Bugs ThripsStriga gesnerioides

False hosts of Striga hermonthica

KVX30-30G-172-1-6KKVX30G-183-3-5KKVX30G-246-2-5KKN-1 (Gousses)IT81D-994KVX 426-9, IT 81D-985,IT 84S-2246 etKVX 426-2

TVU 36KVX 145-27-6KVX 165-14-1KVX 146-27-4KVX 146-1KVX 295-2-124-99

Locale MoussaLocale GaouaLocal KiembaraIT86D-716Sanzisambinli SumbrizolorIT95K-1381KVX 908-1KVX 908-32KVX 910-2

TVU1509TVX3236Sanzisambinli SumbrizolorKVX 404-8-1KVX 165-14-1KVX 404-3J KVX 404-2JLocale de Moussa

KVX61-1KVX30-30G-172-1-6KGorom localB301IT81D-994KVX61-74KVX295-2-124-51IT82D-849HTRWaongo-1

KVX 404-22-2, KVX 396-4-5-2D, KVX 396-4-4, KVX 61-1, KVX 404-19-6G, KVX 442-3,KVX 745-11K, Gorom local,TVU 1509, IT 84S-2246-4 etIT 95K-1479. The TVU 36 variety was the best performing.

Table 2. Crossing with a view of creating large scale adaptation and biotic stress tolerant varieties.Period Constraints Methodologies Achievements

��í��RENACO

High costs of the four insecticide treatments and no longer recommended in production of cowpeas.

Needs for insecticidal treatments vary from a variety to another and from an agroecological zone to another.

1. Identify the critical stages requiring application of insecticides to determine the minimum number of applications for an HFRQRPLFDOO\�EHQH¿FLDO�production.

2. Establish cartography of the need for insecticide treatments by tests with and without insecticide application throughout the three agroecological zones.

1. Two insecticidal applications are VXI¿FLHQW�WR�HQVXUH�HFRQRPLF�SUR¿WDELOLW\�RI�WKH�SURGXFWLRQ�RI�cowpeas for consumption. Selection now under minimum insecticide treatment.

2. A single spray of insecticide against thrips is necessary in the Sahelian zone, in the west and southwest zones, against the sucking pod borer bugs while two sprays remain indispensable in the Sudanian zone outside the cotton zone where treatment should target bugs only. The highest yields without insecticide reaching 750 kg/ha were obtained with Moussa local varieties, KVX 414-22-2, KVX404-8-1, KVX414-22-72, KVX 428-9, KVX 404 - 2J, and IT85D-3516.

3- Insect tolerant varieties: local Moussa, local Bousse, local Mouna, Sanzisambinli, from a regional test in West Africa.

��í��RENACO

Varieties of cowpea adapted to the three agroecological zones of Burkina Faso (i.e., insect, drought, diseases, high temperature tolerant/resistant with culinary qualities) not available.

1. Crossing with adapted biotic stress tolerant local varieties.

2. Multilocational trials with different dates of SODQWLQJ��VFUHHQLQJ�LQ�¿HOG��laboratory, and greenhouse for the LGHQWL¿FDWLRQ�RI�VRXUFHV�RI�resistance/tolerance to different biotic stresses.

The KVx 396-4-5-2D from this selection has the potential for large scale adaptation, CABMV resistance, Striga tolerance, and adaptation in association with cereals. This variety has the capacity to produce both XQGHU�RSWLPDO�FRQGLWLRQV�DQG�GLI¿FXOW�conditions.


Table 2. Continued

��í��PEDUNEPRONAF

Varieties with multiple resistance to main biotic constraints: Striga, aphids, bugs, beetles, brown spots, bacterial canker, gale, drought, high production in Burkina Faso are not available.

Selections made in multilocational trials with and without insecticide, in association with cereals or pure, under strong infestations by insects, Striga, and use of inoculum: direct inoculation of CABMV or infesting lines.

KVX 295-2-124-91: Striga-aphid-weevil resistant; series of 396 KVX: high performance, great adaptability, tolerance to Striga, virus resistance; 414 KVX series: high-performance, large seeds, insect tolerant; KVX61-1: high-yield, Striga resistant, and viruses; KVX 404-8-1, KVX 404-22-2 and .9;��3�KLJK�HI¿FLHQF\��tolerance to thrips, short cycle) Thrips: KVX 404 - 3J and KVX 404 - 2J Sanzisambinli; local Moussa, KVX 404-8-1,.

1994, 2007 et 2008PEDUNEPRONAF

Improved varieties do QRW�SUHVHQW�VXI¿FLHQW�criteria for adoption: the quality of grain for the market and consumers’organoleptic preferences.

Participatory approaches for the diagnosis of the constraints, their updating; involvement of producers in the SURFHVV�RI�¿HOG�selection of lines.

Undergoing extension of varieties of cowpea: KVX 771, KVX 775, KVX 442, TZ

��í�� Despite the existence of molecular markers and potentials in varietal selection, there is no application of these markers in the selection of varieties of cowpea. Few varieties are bug resistant.

Application of methods of marker assisted selection (MAS) in the control of Striga in cowpea; validation of markers; development of MAS protocols crossing of IT 86D-716 with Moussa local.

A protocol is functional for MAS; validation of the markers is being completed; varieties of cowpea close to end of selection from the MAS were being evaluated in three Striga “hot spots” in Burkina Faso in 2010. Three high performing varieties for resistance to bugs: Kvx 908-1; 908 32; 910 2.

Control of stored cowpea pests The need to control bruchids in stored cowpea seeds led to search for alternatives to the use of synthetic insecticides which are generally toxic to man. The major components of the control measures were the use of resistant varieties, the development of botanical insecticides, and biological control.

With regard to host plant resistance, improved varieties already disseminated to farmers were crossed with a source of resistance especially line TVu 2027. Some lines selected from segregating populations showed resistance in seeds or pods (Table 1).

The development of ecologically sustainable methods of protecting grains against C. maculatus damage was based on two principles: (i) to tap into the wealth of endogenous farmer knowledge for generating cheaper, safer, and more sustainable techniques and �LL�� WR� ¿QG�KHUPHWLF� VWRUDJH� WHFKQLTXHV�GHSULYLQJ�EUXFKLGV�RI� R[\JHQ��$�FRPSUHKHQVLYH�directory of insecticidal plants and cowpea storage techniques has been compiled by Dabiré (1985a; 1985b). Tests of raw, macerated, aqueous extracts and extracts by organic


solvents of Cymbopogon schoenanthus (L.) Spreng as well as Hyptis spicigera L. and H. suaveolens Poit on C. maculatus in the laboratory have revealed the insecticidal activity of C. schoenanthus, alcoholic extracts of H. spicigera, and the repellent effect of essential oils from two species of Hyptis (Sanon et al. 2006a; 2006b). The effectiveness of macerates of Cleome viscosa L. and Cassia nigricans Vah. has also been demonstrated by Dabiré et DO��'RVHV�RI��J�RI�PDFHUDWHV�SHU�NJ�RI�VHHGV�KHOSHG�VLJQL¿FDQWO\�WR�UHGXFH�WKH�multiplication of bruchid in a manner comparable, if not more effective than the control with chemical insecticide after two months of storage. Also Spinosad, a natural insecticide has SURYHG�HI¿FLHQW�DJDLQVW�EUXFKLGV��6DQRQ�HW�DO��3UHYLRXVO\�GHYHORSHG�DQG�DGRSWHG�physical control solutions, such as solar drying, double bagging (Murdock et al. 1997), and sealed drums (Seck et al. 1996) are now being replaced by triple bagging developed within the PICS (Perdue Improved Cowpea Storage) project. (Baoua et al. 2012)

Two species of Hymenopteran parasitoids, Dinarmus basalis Round. and Eupelmus vuilleti�&UZ��SDUDVLWL]LQJ��í��RI�EHHWOH�ODUYDH��DW�KDUYHVW��ZHUH�GHYHORSHG�DW�WKH�H[SHQVH�of larvae of the two bruchid species (Ouédraogo et al. 1991; Sanon et al. 2005). It is IURP�WKLV�LQLWLDO�¿HOG�SRSXODWLRQ�RI�EUXFKLGV�DQG�SDUDVLWRLGV�WKDW�WKHLU�IXUWKHU�GHYHORSPHQW�continues in storage. However, the relatively low initial parasitoid population rates are unable to effectively control the growth of beetle populations.

Cowpea diseases Important cowpea diseases in Burkina Faso include both fungi and viruses. Bacterial canker, caused by the bacterial pathogen Xanthomonas vignicola (Bur.) is the only important bacterial disease.

Fungal diseases Major diseases include brown spot, gale, pod rot, rhizoctoniosis, and cercosporiosis. Brown spot can cause seed yield losses of up to 42% in the Sudanian zone of Burkina Faso (Sereme et al. 1992). Owing to its seed transmission nature, this disease is a serious threat to increased cowpea production in the country. To improve the control of brown spot it is necessary to generate and make available information on the pathogen and plant pathogen interactions in addition to identifying sources of resistance to the disease. Previous observations had established that Colletotrichum capsici (90%) and C. truncatum were the agents responsible for the disease. More recent studies have revealed a third taxon of Colletotrichum�FRQ¿QHG�to the Sahel region of Burkina (200–400 mm of rainfall). Pathogenicity studies have revealed the existence of pathogroups both within the complex C. capsici/C. truncatum and within the new taxon. In view of this phenomenon, it becomes imperative to establish a program for identifying new sources of resistance and introgressing these genes into improved and farmers preferred varieties. Different seed storage methods have been investigated with UHJDUG�WR�WKHLU�LQÀXHQFH�RQ�WKH�UDWH�RI�WUDQVPLVVLRQ�E\�C. capsici since seed is the primary source of inoculum for the brown spot disease (Sereme 1998).

Other important seed-borne fungal pathogens such as Colletotrichum spp., Macrophomina phaseolina, and Phoma sp., have frequently been observed with infection rates reaching 52%, 60%, and 22%, respectively. Other fungi such as Fusarium equiseti, F. moniliforme, and F. graminearum are also observed with infection levels ranging from 31 to 61%.


Neem (Azadirachta indica) oil-based soaps, Shea butter (Vitallaria paradoxa), and Balanites aegyptiaca oil have reduced by two thirds, the rate of contamination of seeds by C. capsici (Sereme 1999). Seed treatment with aqueous extracts of Eclipta alba, Balanites aegyptiaca, and Acacia gourmaensis� KDYH� DOVR� JLYHQ� VLJQL¿FDQW� UHVXOWV� LQ� WKH� FRQWURO�of Colletotrichum spp. on seeds. In the Sudanian zone , where the brown spot disease pressure is very important, it has been demonstrated that treating seeds with Benlate T20 �%HQRP\O��7KLUDP��IROORZHG�E\�WZR�IROLDU�DSSOLFDWLRQV�RI�%HQRP\O�DW�WKH�VWDJHV�RI�ÀRZHU�bud and pod formation can effectively control the disease (Sereme and Mathur 1996).

Viral diseases 9LUDO�GLVHDVHV�RQ�FRZSHD�DUH�YHU\�GHYDVWDWLQJ�DQG�GLI¿FXOW�WR�FRQWURO�EHFDXVH�RI�IUHTXHQW�epidemics and lack of curative control methods.

Four major viral diseases affect cowpea in Burkina Faso: cowpea aphid-borne mosaic virus (CABMV), cowpea golden mosaic virus (CGMV), cowpea mottle virus (CMoV), and Blackeye cowpea mosaic virus (BICMV) (Some 1989; Konate and Neya 1996; Neya 2002). The CABMV and the BICMV are endemic on cowpea and on Bambarra groundnut (Vigna subterranea (L.)) Verd. (Neya 2002). The CABMV has four serotypes (I, II, III, IV), serotypes I and IV being newly reported in the country. The BICMV has two serotypes (A, B). Serotype II of the CABMV and serotypes A of BICMV are the most important in terms of severity.

CABMV is the most widespread viral disease affecting 6 to 80% of plants and causing yield losses of 7 to 60% (Somé 1989). The rate of transmission of the virus in seeds is variable depending on the sensitivity of the varieties: 25-40% on susceptible varieties such as Gorom local, Kvx414-22-2, Kvx30-309-6 G, and Moussa local and only 1�2% on the resistant varieties like with Kvx61-1, TVx3236, Kvx65-114, and Kvx396-4-5-2D (Tignégré 2000; Néya 2002). The virus migrates to immature seeds within a period of 4 to 8 days DIWHU�ÀRZHULQJ��$IWHU�WKH�LQIHFWLRQ�RI� OHDYHV�WKH�YLUXV�PXOWLSOLHV�DQG�VSUHDGV�V\VWHPLFDOO\��In seeds, CABMV is more concentrated in the embryo than in the cotyledons (Konaté and Néya 1996). The transmission of CABMV from the plant to the seed is neither due to the sensitivity of the variety to viral infection, nor to the severity of symptoms. Neither is it due to the accumulation of virus in leaves and immature pods, nor to the sequence of formation of the pods. Seed contamination is random in nature and ranges from 0 to 100% in a pod; KRZHYHU��WKH�VHHGV�RQ�WKH�ÀRUDO�VWDON�DUH�PRVW�IUHTXHQWO\�FRQWDPLQDWHG��.RQDWp�DQG�1p\D��1R�VLJQL¿FDQW�UHODWLRQVKLS�FRXOG�EH�HVWDEOLVKHG�EHWZHHQ�WKH�LQIHFWLRQ�UDWH�DQG�\LHOG�losses (Somé 1989).

The role of the seeds in the spread of CABMV The sigmoid (S-shaped) pattern of progress curves of the cowpea mosaic transmitted E\� LQVHFWV� LQGLFDWHV� WKH�SRO\F\FOLF�QDWXUH�RI� WKH�GLVHDVH��7KH�¿UVW� LQIHFWLRQV� UHVXOW� IURP�transmissions from primary inoculum consisting of contaminated seeds. These virus-infected plants are the source of secondary inoculum made by aphids for the spread of the disease. The importance of the development of the disease depends on the amount of available inoculum and the activity of the vector (Neya et al. 2007). The presence of seeds contaminated by CABMV in seed lots can be the cause of strong epidemics especially among varieties of cowpea with strong transmission potential of the virus by seeds. The use of virus-free or low-contaminated seed is important in the control of epidemics of the mosaic virus of cowpea transmitted by aphids.


Impact of the spread of the CABMV per agroecological zoneDespite annual variations, agroclimatic conditions favorable to the growth of plants as well as the population increase of aphid vectors are undoubtedly key factors in the spread of the disease. Thus, the incidence of the disease is higher in Niangoloko in the southern Sudanian zone, and Sapouy and Somnawaye in the Sudanian zone (Néya et al., . 2008). 7KH� OHYHOV� RI� LQIHFWLRQ� UHFRUGHG� LQ� WKHVH� UHJLRQV� SDUWO\� UHÀHFW� WKH� LPSRUWDQFH� RI� DSKLG�populations which decrease from the wet south to the drier north (Dabiré 1992).

New challenges: new biotic stresses on cowpea in Burkina Faso 9HU\�UHFHQWO\��ZH�KDYH�QRWHG�WKH�DSSHDUDQFH�RI�WZR�QHZ�SKHQRPHQD��:H�¿UVW�REVHUYHG�some severe foliar damage symptoms in the Kou Valley, on the Loumbila plains, and in the Sourou during the dry season of 2010 (between March and May). The symptoms looked very similar to damage caused by the leaf thrips, Sericothrips adolfrifridrici Hood (Thysanoptera: 7KULSLGDH��3LFWXUH��EXW�WKH�FDXVDO�DJHQW�FRXOG�QRW�EH�FROOHFWHG�IRU�SURSHU�LGHQWL¿FDWLRQ��The occurrence of this condition is causing a major problem for the production of dry-season cowpea seeds, particularly because in previous years, cowpea seeds could be produced during the dry season when the pressure from key wet season cowpea pests—DSKLG��ÀRZHU�WKULSV��SRG�ERUHUV��DQG�SRG�VXFNLQJ�EXJV²LV�YHU\�ORZ��7KH�RFFXUUHQFH�RI�WKLV�new phenomenon in the past two consecutive years, has made it impossible to increase cowpea production in the irrigated plains of the Kou Valley, the Loumbila plains, and in WKH�6RXURX�ZKHUH�IDUPV�RI�PRUH�WKDQ�¿YH�KHFWDUHV�KDYH�EHHQ�DEDQGRQHG��7KHUHIRUH��WKH�occurrence of this dry season pest needs to be investigated in more detail for the purpose of designing appropriate control measures.

Picture 1 (left and right): foliar damage symptoms suspected to be caused by the leaf thrips 6HULFRWUKLSV�DGRO¿IULGULFL��


Picture 2 (left and right): symptoms of the novel disease in the Donsin/Ziniaré region.

A second phenomenon was observed in various areas of the country but especially in the Sahelian region characterized by low rainfall ranging from 300 to 400 mm in the rainy season. The symptoms include apical drying followed by the discoloration of the leaves and wilting of the plant, occurring at the beginning of the cowpea branching stage. Attacks generally target a few plants in the plot. Preliminary analyses in laboratory showed the presence of a complex of pathogens (Colletotrichum, Macrophomina, Fusarium) (Picture 2).

The parasitic weed Striga gesneiroides Ten varieties have been found to be Striga resistant. A genetic linkage of Cowpea (Vigna unguiculata l. Walp.) has been generated by analyzing the segregation for several types of DNA markers and resistance characteristics among a population of 94 recombinant inbred lines (RIL) from the cross between IT84s-2049 and 524 B. The analysis of 242 new PDUNHUV�PDLQO\� DPSOL¿HG� IUDJPHQW� OHQJWK� SRO\PRUSKLVP� �$)/3�� LGHQWL¿HG� ��PDUNHUV�DVVRFLDWHG�ZLWK�UHVLVWDQFH�RU�VLPLODU�JHQHV�DQG��UDQGRPO\�DPSOL¿HG�SRO\PRUSKLF�'1$�(RAPD), restriction fragment length of the restriction fragment polymorphism (RFLP), and biochemical markers previously mapped have enabled the development of an integrated cowpea genetic linkage map. The new map includes 11 linkage groups (LGs) covering a total distance of 2670 cM, with an average distance of 6.43 cM between the markers. Interestingly, a large continuous portion of the linkage Group 1 which was not included in the earlier maps has been detected. This region extends to about 580 cM and only includes new AFLP markers (54 in total). Several resistance or similar genes are located on the map. These include resistance to races 1 and 3 of Striga gesnerioides, resistance to several virus (CPMV, CPSMV, B1CMV, SBMV) as well as to fusarium wilt and root gall. These markers will be useful as tools for marker assisted selection in cowpea and for possible positional cloning of the different resistance genes.

Conclusion and prospects7KH�PDMRU�FRQVWUDLQWV� OLPLWLQJ�FRZSHD�SURGXFWLRQ�KDYH�EHHQ� LGHQWL¿HG� WR�EH�D�FRPSOH[�of insect pests from seedling to the reproductive phase and seeds in storage. The impact of these pests on the production and quality of cowpea seeds helped to establish the UHODWLYH�HFRQRPLF� LPSRUWDQFH�RI�GLIIHUHQW�SHVWV�� WR�GHVLJQDWH�PDMRU�SHVWV��DQG�WR�GH¿QH�VWUDWHJLHV��7KXV�� WKHVH�DUH� LQVHFWV� LQWHUYHQLQJ�GXULQJ� WKH� UHSURGXFWLYH�SKDVH��ÀRZHULQJ�DQG�SRG�¿OOLQJ��WKDW�FDXVH�WKH�PRVW�GDPDJH��7KULSV��M. sjostedti), the pod borer M. vitrata


drill and the complex of pod sucking bugs including C. tomentosicollis are the dominant pests. However, the problem of insect pests on cowpea persists, because, of the non-GLYHUVL¿FDWLRQ� RI� UHVHDUFK� RQ� WKHVH� LQVHFWV� �-DFNDL� DQG� $GDOOD� �� $SKLG�� VWRUDJH�beetle, sucking bugs, and Striga resistant/tolerant varieties are currently available while research on resistant varieties to thrips and pod borers have not yet achieved conclusive results via the conventional route. With the sustained attention of researchers at IITA and various national programs and international research networks, an integrated approach to the protection of the crop could be established for cowpea growing areas. Research activities on cowpea at INERA in Burkina Faso, IITA, and the national agricultural systems (NARS) have helped to obtain strong results in various areas of control of biotic stresses. The future areas of research relating to the control of cowpea biotic stresses could focus on the axes we have outlined in a non-exhaustive way in this paper. These include:�� Advances in molecular biology and biotechnology (introgression of genes of interest LQ�SRSXODU�YDULHWLHV��DPSOL¿HG�E\�57��3&5�DQG�VHTXHQFLQJ�RI�WKH�YLUDO�JHQRPHV��total or partial) have paved the way to varietal improvement and the reinforcement of NQRZOHGJH�LQ�WKH�¿HOG�RI�ELRWLF�VWUHVVHV��Striga, insects, and diseases. This area will be explored in partnership with scientists from the north to minimize damage from insects, diseases, and Striga��7KH�¿UVW�HYHQWV�RI�%W�FRZSHD�DUH�EHLQJ�WHVWHG�LQ�=DULD��1LJHULD�and will be evaluated in Burkina Faso from 2011, at the Farako-ba research center.

�� Despite the potentials for molecular biology that will certainly help address some of the constraints, it will still be necessary to maintain the conventional strategy of integrated pest control:

– Reinforcing the knowledge on pests and their environment remains essential. – Transfer of resistance genes from varieties, sources of resistance after having

understood the mechanisms of resistance. – Exploring further options to control biotic stresses thus reducing synthetic

pesticides in view of reducing production costs and preserving the environment. – Finally, studies on natural enemies to plan biological control are initiated by

researchers of the subregion against weevil in the University of Ouagadougou, Maruca vitrata by IITA Center for Biological Control at Cotonou and pod sucking bugs Clavigralla tomentosicollis Stäl at INERA. These efforts should be � LQWHQVL¿HG�LQ�RUGHU�WR�SURFHHG�WR�GHSOR\PHQW��

– ,GHQWL¿FDWLRQ�DQG�VWXG\�RI�QHZ�HPHUJLQJ�GLVHDVHV�UHVSRQVLEOH�IRU�VLJQL¿FDQW�� crop losses. We need to maintain the development of technology packages including extension of proven technologies adopted by farmers with a view to � LQFUHDVLQJ�FRZSHD�SURGXFWLRQ��7KLV�FURS�ZLOO�EHFRPH�D�GRPLQDQW�GLYHUVL¿HG�� crop playing a key role in food and nutritional security and providing income to � WKH�IDUPHUV�DQG�¿QDQFLDO�UHVRXUFHV�IRU�%XUNLQD�)DVR�


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An historical review of progress to control key cowpea biotic constraints in Burkina Faso

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