Liquid Culture Systems for in vitro Plant Propagation

Mass propagation of tropical crops 205
3.1 Musa sp. shoot multiplication
Banana shoot multiplication in small TIS vessels was first described by
Alvard et al. (1993), who stressed the advantage of this technique for shoot
development and proliferation in comparison with other liquid culture
systems. However, the commercial application of TIS requires larger
vessels. The use of 10-litre twin flask culture vessels resulted in an excessive
enlargement of the shoots (leave surface and pseudo stem length). This
limited the number of shoots produced per flask and reduced the production
capacity in the growth room. Additionally, handling is more difficult when
dividing and subculturing large shoots, which increases labor costs.
The solution to overcome the problems arising from large shoots is the
reduction of the size of shoots by using growth retardants. Growth retardants
have been successfully used to inhibit shoot length and to promote bud
clusters formation in several species (Ziv, 1992; Ziv et al., 1998).
The application of PBZ and ANC in TIS (1-litre twin flasks) stimulated
bud proliferation (Albany et al., 2002). Both compounds were also effective
in controlling the excessive growth of the shoots and induce the formation of
compact bud clusters. Shoots multiplied in TIS in the presence of PBZ (2.5
mg l -1 ) were successfully transferred to semisolid or liquid rooting media in
traditional culture vessels or in TIS. After 15 days plants were ready for
acclimatization.
The protocol developed was further scaled up in 10-litre TIS using a two
step procedure: first the shoots were multiplied in PBZ (2.5 mg l -1 ) and 6-
BAP (4 mg l -1 ) containing medium for 4 weeks and, inside the same culture
vessels, the multiplication medium was replaced by a hormone-free medium
to promote shoot elongation and rooting (see Chapter 13, Figure 6).
3.2 Solanum tuberosum microtuber production
Potato (Solanum tuberosum L.) microtubers offer several advantages
over in vitro propagated plants, since they can be stored and transplanted
directly into the field without an acclimatization stage. Also handling and
shipping are easier, thus facilitating commercialization and international
exchange of germplasm. The main problems associated with microtuber
production in conventional flasks are the low yield of tubers (1-1.5 tubers
per plant) and the small tuber size that limits direct transplanting to field
conditions.
At the Institute of Plant Biotechnology, Cuba, a temporary immersion
system for potato microtuber production was designed using 4-litre twin
flasks (Jiménez et al., 1999). In both cultivars tested, Desiree and Atlantic,
an average of 3.1 and 2.8 tubers per single node cutting was achieved after 9