In vitro shoot culture and microtuber induction in the steroid yam Dioscorea composita Hemsl

The individual effects of sucrose, plant growth regulators and basal salt media formulations were investigated on microtuber induction and development in shoot cultures of the steroid yam Dioscorea composita. Sucrose at 8% (w/v) was the single most significant medium constituent for microtuber induction. Of the four cytokinins tested, 6-benzyladenine at 1.25 and 2.5 mu M showed strong inhibitory effects on microtuber induction. By contrast, the auxins cu-naphthaleneacetic acid and indole-3-butyric acid at 5.0 mu M showed striking promotive effects on microtuber induction and growth. In the presence of either one of these auxins at 5.0 mu M shoot cultures produced microtubers weighing 300-400 mg fresh weight whilst kinetin, 6-(gamma,gamma-dimethylallylamino)-purine, 6-benzyladenine and abscisic acid failed to promote microtuber growth (microtubers weighed generally <200 mg). Media formulations Lloyd and MacCown and White supported the lowest frequencies of microtuber induction when kinetin was present at 2.5 mu M. Anderson Rhododendron was as effective as Murashige and Skoog overall in promoting both microtuber induction and growth. When removed from cultures and planted in sterilized moist sand, microtubers sprouted readily (60-87% within 2 weeks) and produced vigorous shoot growth and after 5-7 months minitubers of sizes (30-80 g) suitable for direct field planting.