Isozyme diversity in Bambara groundnut

Bambara groundnut (#Vigna subterranea$ (L.) Verdc.) is an important crop in many countries of tropical Africa. Compared with other leguminous crops, little is known about the organization of its genetic diversity. Our goal was to investigate its population structure and the partitioning of genetic diversity between domesticated and wild accessions. Seventy-nine accessions of domesticated and 21 wild Bambara groundnut populations were evaluated for genetic diversity at 41 isozyme loci, representing 23 enzyme systems. Domesticated accessions were characterized by very low genetic diversity (Ht = 0.052) with only 7 polymorphic loci. Wild populations were characterized by higher genetic diversity (Ht = 0.087), with 14 polymorphic. This suggests a marked bottleneck between wild and domesticated forms. Intrapopulation diversity was comparatively high (Hs = 0.033 for domesticated and Hs = 0.025 for wild populations) despite the near absence of heterozygous individuals, which suggests a predominantly selfing mode of pollination in both wild and domesticated Bambara groundnut. High genetic identity between wild and domesticated forms suggests that wild Bambara groundnut is the true progenitor of domesticated Bambara groundnut. Both morphological and isozyme data show a gradient between true wild and domesticated Bambara groundnut through weedy populations. The improved understanding of the organization of genetic diversity of Bambara groundnut provided by our data will allow a better conservation of its genetic resources. (Résumé d'auteur

Une légumineuse alimentaire, le niébé

Le niébé, Vigna unguiculata (L.) Walp., fait partie des principales légumineuses alimentaires mondiales. Il est aujourd’hui cultivé dans toutes les zones intertropicales et même au-delà : bassin méditerranéen, Iran, Chine, sud des États-Unis... Le niébé est, comme le voandzou (Vigna subterranea (L.) Verdc.), une espèce africaine. Les formes spontanées du niébé se rencontrent uniquement en Afrique (elles sont d’ailleurs assez communes dans le nord du Cameroun) où il a été domestiqué, il y a qu..

Organisation du pool génique de Vigna unguiculata (L.) Walp. : croisements entre les formes sauvages et cultivées du niébé

Organization of the genic pool of Vigna unguiculata (L.) Walp. : crosses between the wild and cultivated forms of cowpea. Cowpea (Vigna unguiculata (L.) Walp.) gene pool organization is studied on the basis of intra-specific crossing between cultivated (cv-gr. Unguiculata, cv-gr. Biflora) and wild forms of the species (var. spontanea, subsp. alba, subsp. stenophylla, subsp. pawekiae, subsp. baoulensis). The rate of crosses success, the rate of the obtained pods fruitfulness and the pollinic fertility of the hybrids F1 varied according to the wild taxa used. The highest rate of success was obtained for the crossings between cultivated and annual inbred form (40-79,3%). This result confirms that var. spontanea is genetically closer to the cultivated forms than the other wild forms. Crosses between cultivated and wild allo-autogamous forms gave intermediate rates of success (17,8-57,9%) and a significant reduction of the pollinic fertility of some hybrids F1. These observations suggest the existence of a genetic divergence between these two groups, however they share the same gene pool. The wild allogamous forms gave the weakest rates of success with the cultivated forms (3,1-40%) showing that they are genetically more distant of these last, compared to the other wild groups. The rates of crosses success are particularly weaker when the wild form subsp. baoulensis is crossed with the cultivated forms

Construction of a SSR-based genetic map and identification of QTL for domestication traits using recombinant inbred lines from a cross between wild and cultivated cowpea (V. unguiculata (L.) Walp.)

Cowpea (Vigna unguiculata (L.) Walp.) is a grain legume commonly grown and consumed in many parts of the tropics and subtropics. A genetic linkage map was constructed using simple sequence repeat (SSR) markers and a recombinant inbred (RI) population of159 individuals derived from a cross between the breeding line 524B, a California Blackeye, and 219-01, a perennial wild cowpea from Kenya. Out of 912 primer combinations predicted to amplify SSRs in cowpea, 639 reliably produced amplification products in PCR assays and 202 (31.6%) were polymorphic between the two parents. These polymorphic SSRs were used to construct a genetic map consisting of 11 linkage groups (LGs) spanning 677 cM, with an average distance between markers of 3 cM. Agronomic traits related to domestication (seed weight, pod shattering) were analyzed together with the genotypic data. Six quantitative trait loci (QTL) for seed size were revealed with the phenotypic variation ranging from 8.9 to 19.1%. Four QTL for pod shattering were identified with the phenotypic variation ranging from 6.4 to 17.2%. The QTL for seed size and pod shattering mainly cluster in two areas of LGs 1 and 10, facilitating the use of marker-assisted selection to eliminate undesirable wild phenotypes in breeding activities involving introgression of traits from wild germplasm. The generation of an SSR-based molecular map and additional trait-linked markers also contributes to the expanding tool kit available to cowpea breeders, especially in Africa

Molecular mapping of QTLs for domestication-related traits in cowpea (V. unguiculata (L.) Walp.)

Understanding the genetic basis underlying domestication-related traits (DRTs) of cowpea (Vigna unguiculata (L.) Walp.) is important since the genome has experienced divergent domestication and in addition it is also useful to utilize the wild germplasm efficiently for improving different traits of the cultivated cowpea. Quantitative trait loci (QTLs) for DRTs were identified in a population of 159 F-7 recombinant inbred lines derived from a cross between a domesticated cowpea (V. unguiculata (L.) Walp.) variety, 524B, and a wild accession, 219. Using the constructed linkage map, QTLs for 10 DRTs were analysed and mapped. QTLs for seed, pod and flower related traits were detected. Subsequently, QTL for ovule number was also identified. To our knowledge, this is the first time a QTL for this trait has been observed. QTLs for DRTs show co-localization on three linkage groups and pleiotropy or close linkage of genes for the traits is suggested in these chromosome regions. The information gained in this study can be used for marker-assisted selection of domestication-related QTLs in cowpea and enhance understanding of domestication in the genus Vigna

Inheritance of 'domestication' traits in bambara groundnut (Vigna subterranea (L.) Verdc.)

Controlled crosses in bambara groundnut were attempted between a range of thirty-six bambara groundnut landraces (thirty domesticated (V. subterranea var. subterranea) and six wild (V. subterranea var. spontanea)). Ten F-1 seed were produced. Of these, eight germinated producing F-2 populations. On seed set, four populations could be unambiguously confirmed as true crosses by F-3 seed coat colour. A single F-2 population, derived from a domesticated landrace from Botswana (DipC; female parent) crossed with a wild accession collected in Cameroon (VSSP11; male parent) was used to study a range of agronomic and domestication traits. These included; days to emergence, days to flowering, internode (fourth) length at harvest, number of stems per plant, leaf area, Specific Leaf Area (SLA), Carbon Isotope Discrimination (CID), 100 seed weight, testa colour and eye pattern around the hilum. On the basis of variation for internode length and stems per plant, 14 small F-3 families were selected and grown under field conditions to further investigate the genetic basis of the 'spreading' versus 'bunched' plant character, a major difference between wild and cultivated bambara groundnut. Results presented suggest that traits including leaf area, SLA, CID and 100 seed weight are controlled by several genes. In contrast, the variation for traits such as internode length, stems per plant, days to emergence and seed eye pattern around the hilum are likely to be under largely monogenic control. The results of this work are discussed in relation to the domestication of bambara groundnut

Mapping of quantitative trait loci for floral scent compounds in cowpea (Vigna unguiculata L.)

Floral scent is a very important trait in plant evolution. Currently, little is known about the inheritance of floral scent in cowpea (Vigna unguiculata L.) or changes that might have occurred during its domestication. Therefore, we analysed scent volatiles and molecular markers in a population of 159F(7) recombinant inbred lines derived from a cross of a domesticated blackeye cowpea cultivar, 524B' and a wild accession 219-01'. Using gas chromatography-mass spectrometry (GC-MS) 23 volatile compounds were identified that fall into five general functional categories. Twenty-two of the compounds displayed quantitative variation in the progeny, and a total of 63 QTLs influencing the amounts of these volatiles were mapped onto the cowpea genetic marker map. Although QTLs for volatile compounds putatively involved in cowpea flower scent were found on 9 of the 11 cowpea chromosomes, they were not evenly distributed with QTLs mainly clustered on LGs 1, LGs 2 and LG 4. Our results serve as a starting point for both more detailed analyses of complex scent biosynthetic pathways and the development of markers for marker-assisted breeding of scented rose varieties

Long-distance pollen flow assessment through evaluation of pollinator foraging range suggests transgene escape distances

Foraging range, an important component of bee ecology, is of considerable interest for insect-pollinated plants because it determines the potential for outcrossing among individuals. However, long-distance pollen flow is difficult to assess, especially when the plant also relies on self-pollination. Pollen movement can be estimated indirectly through population genetic data, but complementary data on pollinator flight distances is necessary to validate such estimates. By using radio-tracking of cowpea pollinator return flights, we found that carpenter bees visiting cowpea flowers can forage up to 6 km from their nest. Foraging distances were found to be shorter than the maximum flight range, especially under adverse weather conditions or poor reward levels. From complete flight records in which bees visited wild and domesticated populations, we conclude that bees can mediate gene flow and, in some instances, allow transgene (genetically engineered material) escape over several kilometers. However, most between-flower flights occur within plant patches, while very few occur between plant patches

Atlas de la province Extrême-Nord Cameroun

Réalisé par l’IRD et l’INC (Institut national de cartographie, Yaoundé), l’Atlas de la province Extrême-Nord Cameroun a été publié en avril 2000 en grand format. L’ensemble réunit et synthétise une somme considérable de résultats de recherche collectés, trois décennies durant, par une vingtaine de chercheurs. Trente-neuf cartes, accompagnées de notices très étoffées et d’un grand nombre de graphiques, diagrammes, tableaux et dessins, rendent compte de l’environnement physique, des éléments démographiques, ethniques, archéologiques et linguistiques, et de toute la diversité des ressources agraires. Trois cartes traitent en outre de questions très spécifiques au nord du pays : parcs et végétation anthropique ; aliments de famine ; stratégies de conservation du grain. La présente réédition améliore beaucoup les possibilités de visualisation détaillée sur PC par rapport à la première version cédérom qui accompagnait l’atlas papier. Elle fait partie d’un ensemble de trois cédéroms qui offrent, sous une forme nettement plus compacte, l’ensemble des atlas réalisés par l’Orstom/IRD au Cameroun, dont la plupart sont maintenant introuvables