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2.12 IN VITRO PROPAGATION OF GEOPHYTES
Literature review
ZIV (1997) defines geophytes as plants pereniating by underground storage organs.
Geophytes are generally capable of developing tubers, corms or bulbs in vitro
(STEINITZ & LILIEN-KIPNIS, 1989). Many ornamental geophytes are used for
gardening, pot plant production, flowering pot plant production, cut flower production
and the production of phytochemicals (ZIV, 1997).
Plant biotechnology has provided geophyte production with clonal propagation, virus
elimination, breeding and crop improvement through embryo rescue, in vitro
fertilization, somaclonal variation, protoplast isolation and somatic hybridisation, and
haploid production (ZIV, 1997). Genetic transformation is also aiding in geophyte
development. Benefits include improving horticultural traits and induction of disease
resistance (ZIV, 1997). Gene mapping and DNA fingerprinting are also additional
developing areas (ZIV, 1997).
Micropropagation has been achieved by enhanced axillary bud development,
organogenesis and adventitious bud formation or by somatic embryogenesis (ZIV,
1997). Explants used for propagation of bulbous, cormous and tuberous plants
include the leaf lamina, petiole, mesophyll and epidermis (ZIV, 1997). Inflorescence
peduncle, pedicel, tepals, petals, sepals, ovaries, anthers, ovules and embryos have
also been used (ZIV, 1997). Other explants include the basal plate, scales, twin-
scales and nodal and storage tissue of bulbs, corms and tubers (ZIV, 1997).
The use of the underground pereniating organ as an explant source is often
associated with heavy pathogen contamination (ZIV, 1997). This is a destructive use
of the pereniating organ and eliminates the possibility of further vegetative or
horticultural evaluation (ZIV, 1997). Different parts of the young flower and
inflorescence stem can be cultured (ZIV, 1997). This is a source of pathogen-free
totipotent explants (ZIV, 1997). Totipotency depends on the developmental stage at
time of excision and position from which the explant was isolated (ZIV, 1997).
Explants isolated from tissue positioned immediately next to the basal plate have a
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