Sprouting of microtubers wasalsoobservedmainlyon
cutting nodes cultured on the second- or third-storey ofin vitro
hydroponic system (Fig. 3a,b). This phenomenon seriously
affects the size of microtubers because part of nutrients is
wasted in the development of new buds. Moreover, the cutting
segments on the higher storey tended to develop their buds
than their tubers due to the fact that they could obtain more
light, which is believed to block the formation of new tuber.
Our finding agree with that ofGopal et al. (1998)who reported
an increase in the number of microtubers as the light intensity
was lowered. Besides, high intensity of light in higher storey
induced the formation and development of shoot on the newformed-microtubers. Consequently, the results from this
experiment show that the three-storey hydroponic culture
system can produce more microtubers than the conventional
one involving a solid medium. Substrates like cotton layer or
filter paper can store large quantities of water and nutrient
solution without limiting the gas exchange in the root zone,
enhancing the development and the nutrient accumulation of
microtuber. In this experiment, cotton layers appear to be