Photoautotrophic growth of sugarcane plantlets in vitro as affected by photosynthetic photon flux and vessel air exchanges

Explants of sugarcane, a C-4 plant, were cultured in vitro for 18 d on Florialite (a solid cube consisting of vermiculite and cellulose fibers) used as supporting material with sugar-free Murashige and Skoog liquid medium with double-strength KH2PO4, MgSO4, FeSO4, and Na-2-EDTA in the vessel with enhanced natural ventilation. CO2 concentration in the culture room was kept at 1500 mumol mol(-1) (four times the atmospheric CO2 concentration) during the photoperiod. A factorial experiment was designed with two levels of photosynthetic photon flux (PPF) and three levels of N (number of air exchanges of the vessel). The results were compared with those in the control treatment (photomixotrophic culture using sugar-containing agar medium under low PPF and low N). PPF and N showed significant positive effects on the growth of sugarcane plantlets in vitro. In the photoautotrophic (using sugar-free medium) treatments with relatively high PPF (200-400 mumol m(-2) s(-1)) and high N (2-10 h(-1)), the growth of plantlets was four to seven times greater than that in the control. Also, the culture period for multiplication and rooting was shortened from 30 d in the control to 18 d or less in the photoautotrophic, high PPF, and high N treatments. Use of porous supporting material in photoautotrophic treatments promoted rooting and plantlet growth significantly.