In vitro basal and nodal microtuberization in yam shoot cultures (Discorea rotundata poir, cv. Obiaoturugo) under nutritional stress conditions

Single nodal explants excised from vines of greenhouse-grown white Guinea yam (Dioscorea rotundata poir cv Obiaoturugo) were initiated in vitro on a medium consisting of Murashige and Skoog’s (MS) basal salt supplemented with Gamborg’s B5 vitamins, 0.5 iM benzylamino purine (BAP), 0.1 iM naphthalene acetic acid (NAA), 0.2 iM gibberellic acid (GA3), 20 mgl-1 L-cysteine, 30 gl-1 sucrose and solidified in 8 gl-1 agar. They were incubated for 14 months with regular monthly subculture under continuous illumination at 24 ± 1oC and 1000 lux light intensity. Subsequently, single and double leafed segments from these were transferred to a simpler liquid medium made up of MS basal salts and vitamins, reduced sucrose level (20 gl-1) and without growth regulators. The cultures were kept stationary, and without subculture for 6 months at 27 ± 1oC, 16 h illumination and at 2000 – 2500 lux light intensity. The shoot cultures began to produce excessive roots at the nodes apart from the shoot tip. Subsequently microtubers developed at the position of the axiliary buds subtended by the leaf petiole as well as at the base of some shoots. On transfer whole or segmented into fresh medium, the microtubers sprouted and produced plantlets.