Liquid Culture Systems for in vitro Plant Propagation

Temporary immersion system: a new concept 191
of containers and in material handling, eliminating of cutting and
explantation, elimination of in vitro rooting, and a reduction in
contamination levels.
Long-term maintenance of radiata pine shoot hedges by nutrient
replenishment led to a reduction in manpower requirements, facilitated the
move towards automation and reduced the cost of micropropagated trees
(Aitken-Christie and Jones, 1987). This was the first report on a method of
culturing shoots as hedges for a period of up to 18 months without manual
subculturing. The shoots were harvested in 600 ml glass jars at a rate of 672
shoots per hour and approximately 1,100 shoots were produced per square
metre of agar surface per month. Based on that harvesting rate, this system is
around 7 times cheaper than the normal method of radiata pine shoot
subculturing on agar medium as described by Smith (1985). Culturing in
liquid medium on tilting and rocker machines, as described by Harris and
Mason (1983), led to lower costs by reducing the volume of medium by 50%
and of agar by 90% or more, in addition to gains in shoot yields and shoot
size, and better rooting.
In somatic embryogenesis processes, the late culture phases are the most
expensive, due to the amount of handling required. For instance, with coffee
and banana, for which mass production procedures have been established,
temporary immersion bioreactors are used either for the production and
germination of somatic embryos as for coffee (Etienne-Barry et al., 1999), or
just for germination as for banana (Teisson et al., 1999). The production and
germination of coffee somatic embryos in a temporary immersion bioreactor,
combined with direct sowing of germinated embryos under ex vitro
conditions reduced handling times to 13% and shelving area requirements to
6.3% of the values obtained with conventional acclimatization of plants
developed on agar media (Etienne-Barry et al., 1999). Moreover, the time
spent in vitro was reduced by 3 months.
Scaling-up experiments with temporary immersion systems are currently
under way, with a view to commercial production. For some years, the
French research organization CIRAD has been using mass propagation by
somatic embryogenesis with the RITA � system to disseminate selected F1
hybrids of C. arabica in Central America in cooperation with CATIE and
PROMECAFE institutions and in Tanzania, in cooperation with the ARTI of
Lyamungu. A Cuban team at the Centro de Biopletas in Ciego de Avila is
also preparing for commercial propagation of sugarcane and pineapple using
meristem proliferation techniques with the BIT � twin flasks system.