Growth and carbohydrate changes in shoot cultures of Dioscorea species as influenced by photoperiod, exogenous sucrose and cytokinin concentrations

Abstract

The yams (Dioscorea) are important as staple food and as products for synthesis of sexual and adrenocortical hormones. The vegetative propagation of commercial yams is by tuber-seeds. For medicinal uses, this system has several limitations, including long periods required for wild species to reach commercial production, the labour of cultivation and harvesting and the small number of tubers available. In the present investigation, two native species from Brazil, Dioscorea delicata R. Knuth. and D. olfersiana Kl., and the exotic species, D. bulbifera L. from Asia, were cultured in vitro under different daylength and in different concentrations of 6-benzylaminopurine and sucrose, and the leaves were analysed with respect to soluble carbohydrates, starch and proteins. The best explants for vegetative propagation were those with two or more nodal buds, although the culture conditions used did not stimulate bulbil production. Glucose and fructose were the major soluble carbohydrates present in the leaves and sucrose was found only in D. olfersiana. With increasing concentrations of 6-benzylaminopurine (0–22 μM) and sucrose (1.5–8%), an accumulation of soluble carbohydrates and starch was observed, while the amount of soluble protein remained constant. The number of leaves produced and the age of cultures were positively correlated, despite the absence of significant differences among treatments.