Effect of sugar, agar concentration of medium and light intensity on growth and carbon absorption of Ipomoea batatas (L.) Lam

The effects of sucrose and agar concentration in the media, and light intensity on growth and carbon absorption were observed using the plantlets of sweet potato (Ipomoea batatas (L.) Lam.), The stem cuttings with one leaf dissected from in vitro cultured plantlets were cultured under 12 degrees of combinations of three sugar levels (5, 20, and 45 gl-1) and two agar levels (5 and 10 gl-1) in medium, and two levels of PPFD (50 and 100 μmol m-2 s-1) maintained at an air temperature of 25±1°C and a carbon dioxide concentration of 1, 000 μmol mol-1. The dry weight of the plantlets increased as the sugar concentration and/or light intensity increased. Under high agar concentration, the shoot growth declined, but the root growth accelerated. Absorbed molar quantity of carbon dioxide was more in high concentration of agar or high light intensity. The plantlets which was inhibited the sugar absorption by the high agar concentration seemed to depend more on CO2 as a carbon source. It may be suitable that the media contain high sugar and agar concentration in early stage for heterotrophic or mixotrophic growth of the plantlets, and then CO2 concentration and light intensity are gradually raised for their mixotrophic or autotrophic growth according to the status of the plantlet.