Résumé
Yams are an important food crop in tropical and sub tropical regions. Dioscorea alata or the greater yam, is the most widely distributed species throughout the tropics. It has a great potential for yield, a good storage quality (3-5 months) and can be easily machine harvested. However, several factors limit its development. These include abiotic and biotic constraints, including anthracnose disease as a constant threat. D. alata includes varieties with three ploidy levels 2n= 40, 60, 80 chromosomes. A recent study has shown that the accessions are di ploid, triploid and tetraploid respectively (2n=2x, 3x, 4x), and not hexaploid and octoploid as previously assumed. Ploidy increase is correlated with growth vigour, higher tuber yield and increased tolerance to abiotic and biotic stress. Although polyploidy has been recognized for a long time, all breeding programs were exclusively based on the creation of diploid varieties, until 2006. The first triploid and tetraploid hybrids were recently create d by conventional hybridization through the discovery of the fertility of tetraploid varieties and development of an in vitro immature embryo rescue method. Three promising hybrids are under evaluation in farming systems using participatory approach in Guadeloupe and Martinique. The several possible ways that could be exploited to produce polyploids have been studied. Progress could be reached through the use of biotechnological tools (cytogenetic techniques and molecular markers). It has been demonstrated that some diploid varieties are able to produce unreduced 2n gametes and that this phenomenon can be used to create polyploids. Polyploidy breeding opens the way to develop hybrids with higher yields, combined with tuber characteristics adapted to commercial production (quality, tuber shape, etc.) and resistance to anthracnose disease. (Texte intégral)