Studies on the formation of aerial tubers in Chinese yam. (II)

Abstract

In order to examine the role of sugar for aerial tuber formation, sterile culture of vine segments was undertaken using various nutrient media. The results may be summarized as follows: (1) No tuber formation was seen in the medium containing inorganic salts alone. But when sucrose was added to the medium, the vine segment was rendered to form aerial tubers, an evidence show-ing the necessity of sugar for tuber formation. (2) The size of tubers became increasingly larger in proportion to the concentration of sugar applied to the nutrient media. (3) So long as uniform materials were used, the initiation of tubers occurred simultaneously re-gardless of the sugar concentration in the medium. (4) The time required for tuber initiation was correlated with the growth stage (or maturity) of vines, namely, less time was required for mature vines. (5) At the time the tubers began to emerge, progressively more sugar was found in the vine tis-sue as the sugar concentration in the medium in-creased. However, in case of the medium containing 2% sugar, the sugar content of the vine segment became lower than the initial content. Nevertheless the tuber formation occurred. Hence the increase in sugar content in the tissue itself seems not responsible for the induction of aerial tubers, though it is conceivable that sugar is necessary for tuber formation and subsequent growth of tuber depends upon the sugar concentra-tion in the medium.