Abstract
The nutritional and hormonal requirements for the growth of callus derived from root-tuber tissue of sweet potato "var. Kokei No. 14" are described in the present investigation. When the tissue disk derived from root-tuber was placed on an agar medium containing White's minerals, 2% sucrose, yeast extract and auxin, a callus formed and developed on the surface of the disk, and in subculture it grew speedily and continuosly on the same medium. The favorable concentration of yeast extract for the formation and growth of callus was 0.3∼0.5%, and when the amount of yeast extract in the medium was lower than 0.2% there was no continuous growth of callus. From the result of partially substituting casamino acid (0.1%) and kinetin (0.01mg/l) for the large amount of yeast extract, it may be suggested that the growth-promoting activity of yeast extract for the callus of sweet potato was fairly attributed to its cytokinin and amino acids. It was also reported that for the formation and growth of callus exogenous auxin is necessary. 2, 4-D (0.1∼1mg/l) as well as NAA (10∼20mg/l) stimulated the callus formation and maintained its growth, but IAA was ineffective in this respect. In rare case, root formation occurred in the callus on the NAA-medium, but there was no sign on the medium containing 2, 4-D. The favorable concentration of sucrose for the formation of callus of the tissue disk was found to be 5%, but in subculture 2% sucrose showed the excellent growth of the callus.
