Efficacy of a cry1Ab Gene for Control of Maruca vitrata (Lepidoptera: Crambidae) in Cowpea (Fabales: Fabaceae)

Cowpea [Vigna unguiculata (L) Walp.] is an important staple legume in the diet of many households in sub-Saharan Africa. Its production, however, is negatively impacted by many insect pests including bean pod borer, Maruca vitrata F., which can cause 20–80% yield loss. Several genetically engineered cowpea events that contain a cry1Ab gene from Bacillus thuringiensis (Bt) for resistance against M. vitrata were evaluated in Nigeria, Burkina Faso, and Ghana (West Africa), where cowpea is commonly grown. As part of the regulatory safety package, these efficacy data were developed and evaluated by in-country scientists. The Bt-cowpea lines were planted in confined field trials under Insect-proof netting and artificially infested with up to 500 M. vitrata larvae per plant during bud formation and flowering periods. Bt-cowpea lines provided nearly complete pod and seed protection and in most cases resulted in significantly increased seed yield over non-Bt control lines. An integrated pest management strategy that includes use of Bt-cowpea augmented with minimal insecticide treatment for protection against other insects is recommended to control pod borer to enhance cowpea production. The insect resistance management plan is based on the high-dose refuge strategy where non-Btcowpea and natural refuges are expected to provide M. vitrata susceptible to Cry1Ab protein. In addition, there will be a limited release of this product until a two-toxin cowpea pyramid is released. Other than South African genetically engineered crops, Bt-cowpea is the first genetically engineered food crop developed by the public sector and approved for release in sub-Saharan Africa

Distribution and diversity of alternate hosts of Maruca vitrata Fabricius in three West African countries

The evolution of resistance to the Bacillus thuringiensis (Bt) toxins by insect pests is a major threat to Bt technology. However, the rate of resistance can be slowed with appropriate integrated insect resistance management (IRM) strategies. Surveys were conducted to identify alternate host species for Maruca vitrata (commonly called the legume pod borer or Maruca) that could serve as refuges for Pod-Borer Resistant (PBR) cowpea in three West African countries (Ghana, Nigeria, and Burkina Faso). Survey sites included 25 in northern Ghana, 44 in northern Nigeria, and 52 in north-central and southwestern Burkina Faso. Alternate hosts of Maruca identified from plant species belonging to the Fabaceae family that showed signs of Maruca damage on cowpea tissues were collected and dissected. Larvae that were found during these dissections were reared to adult moths in the laboratory then identified to species. The alternate host plants including species of Crotolaria, Sesbania, Tephrosia, and Vigna were the most frequently encountered among sites and locations. Flowering and podding of these plants overlapped with flowering and podding of the nearby (~200 m) cowpea crop. Abundance of these wild hosts and overlapping flowering patterns with the cowpea crop in most locations have the potential to sustain ample numbers of Bt susceptible Maruca that will mate with possible resistant Maruca and deter resistance development. Further quantitative studies, however, are required from each location to determine if actual Maruca production from alternate hosts is sufficient for a PBR IRM strategy. If verified, this approach would be compatible with the high dose/refuge IRM strategy that includes alternate hosts and non-Bt crops as refuges

Caractérisation agro-morphologique et moléculaire de cultivars locaux de niébé (Vigna unguiculata) du Burkina Faso

Les écotypes locaux de niébé collectés à la fin des saisons pluvieuses 2000 et 2001 ont été séparés (pour chaque écotype) par les paysans en un ou plusieurs composantes selon la couleur du tégument ou de l’oeil, la texture ou la taille de la graine. Les mélanges sont plus fréquents quand les cultivars ont la même couleur. De 122 cultivars collectés, 1.4 composante en moyenne a été détectée. Les évaluations faites en plein champ en contre saison et en saison pluvieuse ont révélé que les cultivars appelés Beng-yaanga ou Beng-maasga sont de long cycle et sensibles à la photo période. Plusieurs caractères agro-morphologiques ont été déterminés et permettent d’opérer des choix judicieux pour des utilisations aux fins de production ou de recherche. La caractérisation moléculaire réalisée grâce à l’amplification PCR avec des amorces SCAR et la technique AFLP sur un nombre restreint de cultivars a confirmé l’efficacité des deux méthodes pour caractériser les cultivars mais la technique AFLP permet une analyse beaucoup plus fine.Mots clés : Pureté, niébé, caractérisation moléculaire, Burkina.The local ecotypes of cowpea collected at the end of the rainy seasons 2000 and 2001 have been separated (for each ecotype) by farmers in one or more components according to the color of integument or the eye, texture or size of the seed. The mixtures are more frequent when the cultivars have the same color. From 122 cultivars collected, averaging 1.4 components has been detected. The field assessments were made during dry and rainy season have shown that cultivars called Beng-yaanga or Beng-maasga has late maturing period and sensitive to the photo period. Several agromorphological characteristics have been determined and can be used to select cultivars for production or research. The molecular characterization was tested using two techniques namely PCR amplification with primers SCAR and AFLP technology on a limited number of cultivars. The profiles have confirmed the effectiveness of two methods for characterizing cultivars but AFLP technology allows a more detailed analysis.Key words: Purity, cowpea, molecular characterization, Burkin

Genetic structure and mating system of wild cowpea populations in West Africa

Background: Cowpea is a highly inbred crop. It is part of a crop-weed complex, whose origin and dynamics is unknown, which is distributed across the African continent. This study examined outcrossing rates and genetic structures in 35 wild cowpea (Vigna unguiculata ssp. unguiculata var. spontanea) populations from West Africa, using 21 isozyme loci, 9 of them showing polymorphism. Results: Outcrossing rates ranged from 1% to 9.5% (mean 3.4%), which classifies the wild cowpea breeding system as primarily selfing, though rare outcrossing events were detected in each population studied. Furthermore, the analyses of both the genetic structure of populations and the relationships between the wild and domesticated groups suggest possibilities of gene flow that are corroborated by field observations. Conclusions: As expected in a predominantly inbred breeding system, wild cowpea shows high levels of genetic differentiation and low levels of genetic diversity within populations. Gene flow from domesticated to wild cowpea does occur, although the lack of strong genetic swamping and modified seed morphology in the wild populations suggest that these introgressions should be rare