Déterminisme du sexe chez les ignames cultivées Dioscorea rotundata (Poir.) du Bénin

Cultivated yam (Dioscorea rotundata) is a staple tuber crop in West Africa that is mainly propagated vegetatively. Although the majority of yam cultivars flower, the control of its sexual reproduction - in particular sexual expression - remains largely unknown despite its importance for breeding programs. Our objectives were to: 1) characterize the flowering phenology and identify the causes of sex variation in this species; 2) analyze the genetic and hormonal controls of sex determinism; and 3) study the performance of sexual reproduction in monoecious cultivars. Our histological study showed that during floral morphogenesis, stamen and carpel primordia are initiated in all flowers irrespective of sex, but while only primordia corresponding to the sex of the flower continue to develop in sex-stable plants, male and female flowers of sub-dioic populations retain remnants of organs of the opposite sex. Our results also showed that the sex variation of the offspring was more related to the sex of the parents (monoecious in this case) than to the tuber sections used as seed tubers. Our genetic study did not identify a clear genetic marker for early determination of sex identity in D. rotundata yams from Benin but supported the involvement of a genetic locus (Z-) in sex expression with a possible transition from a ZZ/ZW female heterogamous system to an XX/XY male heterogamous system. Our hormonal analyses showed that jasmonates (MeJa) had a masculinizing effect in monoecious plants and that application of MeJA and cytokinins (BAP) accelerated flowering and increased inflorescence production. Furthermore, our crossing results showed that flowers of monoecious plants were fertile and showed a reproductive performance comparable to that of dioecious plants, so that they can partially compensate for the scarcity of female flowers in breeding programs. Altogether, our study has improved our understanding of the control of sex in cultivated yam (Dioscorea rotundata).