Photocontrol of Dioscorea alanta plantlet growth

Light quality evaluations were conducted on yam (Dioscorea alata L. cultivar 'Oriental' ) plantlets to determine the potential usefulness of manipulation of the light environment in regulating growth. Eight-week old, in vitro grown yam plantlets were transferred to pots and treated in vivo with end-ofday (EOD) red (R) or far-red (FR) light. Also, nodal segments ofD. alata plantlets were cultured on Murashige and Skoog basal medium and exposed in vitro to EOD R or FR light. EOD FR light increased internode elongation in both the in vivo and in vitro evaluations, but stimulated petiole elongation and protuber number and dry weight per plant only in the in vivo evaluation. EOD FR light enhancements of internode and petiole elongation and protuber development in these evaluations were reversed by immediately following far-red with red light, suggesting the involvement of phytochrome in these photoreversible processes. Photosynthetic photon flux density (PPFD) evaluations with white (fluorescent) light indicated that leaf, node, and root production per plant from D. alata segments on Murashige and Skoog basal medium was enhanced when subjected to higher PPFD (67 and 107 pmol m -2 s~ ).