Photoperiod affects the growth and development of yam plantlets obtained by in vitro propagation

The effects of photoperiod on the development of in vitro grown plantlets of yam (Dioscorea alata L.), were investigated. Plantlets were transplanted into pots, acclimatizated until they reached vegetative stages V₁ (3 leaves) or V₂ (8 leaves), and then grown under 12-h or 16-h photoperiod. The formation and development of underground tubers was only induced under 12-h photoperiod. Tuber initiation was not related to the initial vegetative stage of plants, and the tubers were visible at about 18 – 24 d. On the contrary, a 16-h photoperiod inhibited tuber formation and stimulated vine and leaf growth. The total dry matter production and the number of leaves per plant of V₁ stage plants were 50 and 30 % lower respectively, after 44 d under 12-h compared to 16-h photoperiod. These parameters were not influenced by photoperiod in V₂ stage plants. Consequently, the effect of 12-h photoperiod on dry matter of V₁ plants was attributed to a source limitation related to the early initiation of tuberization. The transfer of plants grown under 12-h to 16-h photoperiod stopped tuber growth and starch accumulation. On the other hand, it stimulated the shoots and the roots to grow.Abbreviations

LD	long day (16 h)
SH	short day (12 h)

The present study was supported by the Regional Council of Guadeloupe.