The effects of plant growth regulators, light intensity, and end-of-day (EOD) light quality treatments on node and microtuber induction (% of cultures with microtubers) and development (fresh weight of microtubers) in yam (Dioscorea alata L. cv. Oriental) cultures were investigated. Nodal segments were excised from plantlets cultured on tuberization medium containing growth regulators and exposed to various light treatments. Absciscic acid (1 μM) stimulated and cytokinins (2.5 μM) inhibited microtuber development from yam nodal segments cultured on Mantell's and Hugo's full-strength tuberization medium under 8-h photoperiods. EOD far-red (FR) light inhibited microtuber induction and development and enhanced node formation. EOD FR light effects were nullified by immediately following the FR treatment with red light. This suggested the involvement of phytochrome in these processes. The lowest light intensity evaluated (12 μmol m-2 s-1) inhibited microtuber, root and shoot production as compared to light intensities of 42, 72 and 102 μmol m-2 s-1. Kinetin (2.5 μm) in half-strength tuberization medium inhibited microtuber induction and development but did not affect node production in the light intensity evaluation.
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