THE INFLUENCE OF PLANT-GROWTH REGULATORS AND LIGHT ON MICROTUBER INDUCTION AND FORMATION IN DIOSCOREA-ALATA L CULTURES

The effects of plant growth regulators, light intensity, and end-of-da y (EOD) light quality treatments on node and microtuber induction (% o f cultures with microtubers) and development (fresh weight of microtub ers) in yam (Dioscorea alata L. cv. Oriental) cultures were investigat ed. Nodal segments were excised from plantlets cultured on tuberizatio n medium containing growth regulators and exposed to various light tre atments. Abciscic acid (1 muM) stimulated and cytokinins (2.5 muM) inh ibited microtuber development from yam nodal segments cultured on Mant ell's and Hugo's full-strength tuberization medium under 8-h photoperi ods. EOD far-red (FR) light inhibited microtuber induction and develop ment and enhanced node formation. EOD FR light effects were nullified by immediately following the FR treatment with red light. This suggest ed the involvement of phytochrome in these processes. The lowest light intensity evaluated (12 mumol m-2 s-1) inhibited microtuber, root and shoot production as compared to light intensities of 42, 72 and 102 m umol m-2 s-1. Kinetin (2.5 mum) in half-strength tuberization medium i nhibited microtuber induction and development but did not affect node production in the light intensity evaluation.