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2.9.4 Liquid culture
Literature review
In liquid culture, the explant is covered by the medium; enlarging the surface area for
absorbing nutrients and plant growth regulators (ASCOUGH & FENNELL, 2004). The
medium can be changed automatically, this reduces labour costs of subculturing
(ASCOUGH & FENNELL, 2004).
Liquid culture does however have a few side-effects (ASCOUGH & FENNELL, 2004).
Because of the submersion of tissue, the explant may become oxygen deficient. This
leads to the formation of elongated and hyperhydric leaves (ASCOUGH & FENNELL,
2004). There are a few methods to overcome hyperhydricity, they are however not
universal and some of them retard growth and multiplication (ZIV, 1989; ASCOUGH
& FENNELL, 2004).
Gladiolus bud explants have been propagated in an agitated liquid medium (ZIV,
1989). ZIV (1989) concluded that liquid cultures can be used to scale up the
micropropagation of Gladiolus sp. and possibly other geophytes as it allows for a
faster rate of cormlet production (ZIV, 1989).
2.9.5 Embryo-excision
Embryo rescue is known as one of the earliest and most widely used techniques for
Iridaceae micropropagation (KRIKORIAN & KANN, 1986). Embryo culture is a well
established branch of in vitro culture and is known as one of the oldest and most
successful culture procedures (HU & ZANETTINI, 1995; REED, 2005). In embryo
rescue, the artificial medium substitutes for the endosperm (REED, 2005).
MURASHIGE & SKOOG (1962) is the most frequently used basal media for embryo
culture.
Embryo development occurs in two phases, a heterotrophic and an autotrophic
phase (REED, 2005). In the heterotrophic phase, the young embryo, or “proembryo”,
requires a complex medium. In vivo grown embryos at this stage are dependent on
the endosperm. Amino acids such as glutamine and asparagine are often added to
the culture medium.
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