Some breeding aspects of yam (Dioscorea spp.)

The genetical improvement programme of the yam (Dioscorea spp.) can benefit now from the knowledge of the genetic resources which, if better described and analysed, will contribute to it, through international exchange and increased recombination. But the knowledge of the sexual reproduction system and the knowledge of the in vitro culture possibilities strengthened by the techniques of molecular biology are essential. The breeding programmes undertaken bear experimental data and theoretical basis. From the progenies of hybridization of D. opposita since the 19th century, to the promises of D. alata today, through the progenies of the sapogenin-bearing yams, of D. trifida, D. dumetorum and, above all, D. cayenensis-rotundata, the contribution of varietal improvement to the modernization of the crop has gained credibility. It could sometimes lead to good fruit-setting, regular tuber shape and good yield of high commercial value without staking. But, these performances are far from being generalized and cannot be easily associated with adaptation to extreme ecologies, resistance to anthracnose and virosis, among other traits. Biotechnology, through protoplast fusion and generic engineering with. Agrobacterium or biobalistic applied to yam, makes feasible remodelling even more related to the genetic diversity of the Dioscorea genus, in view of developing a major production system for a number of tropical countries.