Gene pool organization of wild and cultivated forms of the food legume, Vigna unguiculata (L.) Walp. | Organisation du pool genique de formes sauvages et cultivees d'une legumineuse alimentaire, Vigna unguiculata (L.) Walp.

Vigna unguiculata (L.) Walp., commonly named cowpea or "niebe" is one of the main food and forage legumes in the African continent, from where it is originating. Within the V. unguiculata complex, three groups are considered: the cultivated forms, the spontaneous annuals forms both, genetically related and the spontaneous perennial forms. The latter present a very large genetic diversity but have not yet been tested and integrated in breeding programmes. Our work contributes significantly to a better knowledge of plant genetic resources of V. unguiculata in Africa and shows the possibilities to obtain new sources of genetic variability, especially to overcome crop pests and diseases. Two studies were undertaken in the framework of our research. Cultivated forms of Vigna unguiculata collected in traditional farming systems in Algeria (north mountains of Kabylia and oasis) revealed, on the basis of isozymatic electrophoresis, a low genetic diversity as it is the case for the whole cultivated forms of the food legume in the African continent. However, the conservation of these traditional landraces became urgent before they are completely lost. Future investigations should consider the exploitation of this material for their drought resistance potential, especially in the Saharian landraces, well adapted to arid environment. Study of F1 hybrids behaviour has allowed to check hypothesis concerning the gene pool organization of the food legume and to suggest a strategy of improvement based upon the exploitation of wild forms. Although hybridizations were carried out within the species V. unguiculata, between parents at the rank of subspecies as defined by Pasquet (1994), our study pointed out substantial incompatibility barriers, particularly between outbreds and out-inbreds. Cytogenetic studies of the hybrids baoulensis x tenuis and baoulensis x letouzeyi did not show major disturbances at metaphase I and II levels. On the stigma, pollen could germinate but the pollen tubes growth was considerably delayed. Few pollen tubes could reach ovules but the fecundation did not take place normally. A high percentage of young pod abortion 24 to 48 hours after pollination could result from problems at post-fertilization levels. Crossing trials have allowed to suggest the presence of two gene pools. The first gene pool would include the following taxa subsp. unguiculata (cultivated), var. spontanea, subsp. alba, subsp. pubescens and subsp. tenuis. The second gene pool would include the following taxa subsp baoulensis, subsp. letouzeyi, subsp. pawekiae, subsp. burundiensis and subsp. stenophylla.