Ecophysiological Studies on Growth and Enlargement of Tubers in Yams (Dioscorea spp.)

1.Development of bioassay method using microtubers of yams

Abstract

This investigation was, therefore, carried out for the purpose of developing a new bioassay method, using in vitro microtuber of yam (Dioscorea alata L., cv. Solo Yam), detecting the activity of the endogenous growth substances considered to induce the growth and enlargement of tubers.
The effects of four kinds of media, mineral composition, sucrose concentration (0, 2, 4, 6, 8, 10%), photoperiod (0, 8, 12, 16, 24h) and growth regulators (NAA, IAA, ZR, JA-Me, ABA) on the development of microtubers, roots and shoots in nodal stem segment cultures of D. alata L. (cv. Solo Yam) were evaluated.
Microtuberization in nodal stem segment occurred on all of the media supplemented with growth regulator and sucrose. Among basic media, 1/2 MS medium was the best on microtuber induction. NAA was most effective among the growth regulators. Optimum NAA concentration was 1mg/l. The microtuberization was the highest at the concentration of sucrose 6%.
When the nodal stem segment cultures were held under 0-h photoperiods (total darkness), the tuberization was incredsed markedly compared to those under light condition. It was also noticeable that the culture in medium with NAA produced only microtubers and roots, but no shoots in nodal segments.
In this study, the optimal medium composition for microtuberization in nodal stem segment was found to be 1/2-sterngth MS medium supplemented with 1mg/l NAA and 6% sucrose held under dark condition at 25°C. And it was reasonably cosidered that the microtubers produced could be used for the bioassay detecting the activity of the endogenous growth substances.