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Cultivated yam (Dioscorea rotundata) is a staple tuber crop in West Africa which is mainly vegetatively propagated. Although the majority of yam cultivars flower, the control of its sexual reproduction remains largely unknown despite its importance for plant breeding programs. While described as a dioecious species, it has several monoecious cultivars that are often subject to spontaneous sex changes. This study aims to evaluate the impact of phytohormones (cytokinins and jasmonates) on sex expression and flower development in cultivated yams D. rotundata. Exogenous applications of 1 mM 6-benzylaminopurine (BAP) and 1 mM methyl jasmonate (MeJa) were performed on seedlings of monoecious (Katala and Laboko), female (Gnidou, Anago) and male (Flou) cultivars. Monoecious cultivars produced monoecious, male and female plants while female and male cultivars had rather stable sex. Our results showed that MeJa had a masculinizing effect in monoecious cultivars and induced inflorescence and flower malformations in female cultivars (56% in Gnidou and 37% in Anago). Most malformations were inflorescence branching and sterile flowers (non-differentiated ovary) with extra cycles of sepals. Moreover, MeJa reduced flowering time in cultivars of all sexes and increased the number of inflorescences per plant as well as the number of flowers per plant. Our results showed that BAP reduced the flowering time, synchronized flowering in female plants and increased the number of inflorescences per plant in monoecious cultivars. However, our results did not allow strong conclusions regarding the effect of BAP on sex expression due to the high proportion of female flowering in both control and BAP sprayed plants. Nevertheless, we did not observe any masculinizing effect for BAP. Further research that would highlight hormone and homeotic gene interactions in flowering could be of key interest in understanding hormonal control of sex in cultivated yams D. rotundata. |
