Liquid Culture Systems for in vitro Plant Propagation

Nutrition of plants in greenhouses and in vitro 489
leaves had a lower content of Ca and K than for plants grown at a “normal”
humidity. Also that in short days the air humidity during the night had a
more pronounced effect than that during the day. Experiments with Eustoma
show that high air humidity is the main reason for tip burn and a lower Ca in
the tips of the leaves (Islam et al., 2004).
The air humidity in a micropropagation system is close to saturation and
therefore reduces the Ca uptake. Therefore there is a need to give a higher
Ca concentration, and consequently, a higher conductivity in a
micropropagation media. Roche and Cassells (1996) found high humidity to
cause shoot-tip and leaf-tip necrosis in nodal cultures of Helianthus
tuberosus. They suggest that an alternative to increasing the Ca content of
the medium could be to reduce the humidity by using more permeable
plastic film to cover the cultures or using bottom-cooling of the incubation
room shelves.
Figure 1: Populus cultivated in vitro with 3000 lux (45 �mol m -2 s -1 ) indicating Fe-
deficiency (left) and cultivated with 1000 lux (15 �mol m -2 s -1 ): no Fe-deficiency symptoms
(right).