The large geophytic monocotyledon, Hypoxis colchicifolia Baker, has been identified for the
importance of its corm extracts in the development of a potential non-toxic prodrug for the
treatment of inflammation, certain malignancies and HIV-infection. The underground corms
of this plant are also commonly used for therapeutic applications in traditional medicine in
Kwazulu-Natal where it primarily occurs. A review of published literature revealed, however,
that H. colchicifolia plants are currently harvested in an unsustainable manner from
traditional collecting sites due largely to population growth, increased land use for urban
development and agriculture, and the popularisation of Hypoxis plants for herbal remedies.
A further search of historical records established that H. colchicifolia plants were dominant
in grassland vegetation prior to 1950, but had rapidly declined since then. Quantitative data
subsequently gathered in this study from comparative surveys of both H. colchicifolia and
H. hemerocallidea populations from sites with near-pristine, disturbed, burnt and mown
grassland vegetation showed for the first time that exposure to human activity and the
grassland management practices of mowing and burning incurred not only a 75% reduction
in plant density of both these Hypoxis species, but also the total destruction of mature plants
of H. colchicifolia in frequently mown and burnt areas. Flowering data recorded in these
surveys, and confirmed by monitoring field performance of cultivated H. colchicifolia plants,
showed that a contributing factor to the plant's inability to withstand these pressures was
that juvenile forms only reached flowering maturity after three to four years growth, thus
adversely affecting seedling recruitment. It was concluded therefore that, since Hypoxis
species responded differently to mowing and burning, geophytic plants should be
considered individually and not as "forbs" during the planning of grassland management
programmes for natural conservation areas.
The need to cultivate H. colchicifolia to ensure its survival was also established using the
new field data gathered in this study. Methods to propagate this species have, however, not
been established. Data gathered on all the plants comprising a single population confirmed
that mature plants survive to an estimated 20 years and longer in natural areas. Greatest
hypoxoside yields were also obtained from corms with a fresh mass of 350g to 400g. Since
these corms were estimated to be 10-years-old and older, propagation and cultivation
methods that could sustain plant production and survival for long periods, and therefore
increased hypoxoside yields, would have to be developed. Several micropropagation systems suitable for the mass production of H. colchicifolia and
from which phenotypically normal plantlets were recovered, were therefore established via
organogenesis, embryo culture and somatic embryogenesis. The latter cultures have not
been reported previously for Hypoxis. In the former culture the toxic effects of phenolic
leachates and browning were controlled, and improved plantlet regeneration achieved, by
adding polyvinyl pyrrolidone to the medium and introducing distinct sequential aseptic steps
into the micropropagation procedure developed.
Defined protocols for the different phases of in vitro somatic embryogenesis are not readily
available for monocotyledons, however, neither are the factors controlling embryogenesis
and organ regeneration known. In this study the process of somatic embryogenesis from
excised zygotic embryos of H. colchicifolia was shown to be complex and the resultant
cultures very heterogeneous. Although the stage of development of the zygotic embryo
explants was important at the time of inoculation, data showed that the induction and
regulation of the processes of embryo culture and somatic embryogenesis were ultimately
determined by the exogenously applied plant growth regulators.
By comparing the different pathways leading to plantlet regeneration, and the morphological
stages of development of the structures produced both on solid and in liquid media, not only
photographically, but also quantitatively and schematically, the repeated formation of
pseudoembryonic structures and neomorphs confirmed that they form an integral part in the
in vitro somatic embryogenic pathway of H. colchicifolia. Evidence suggested not only that
two types of somatic embryos are produced in the embryogenic cultures of H. colchicifolia,
but that the pseudoembryonic structures produced resemble the pseudobulbils produced
in polyembryonic cultures of Citrus.
The success of the somatic embryogenic cultures was confirmed by the estimation that
28 112 somatic embryos and embryo clusters of H. colchicifolia could be obtained from
16 ml of somatic embryogenic liquid culture. Furthermore phenotypically normal plantlets
regenerated from all of the micropropagation procedures developed were successfully
transplanted from the laboratory, acclimatized under greenhouse conditions and their
horticultural and field performances evaluated. / Thesis (Ph.D.)-University of KwaZulu- Natal, Pietermaritzburg, 2004.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10081 |
| Date | 27 November 2013 |
| Creators | Appleton, Margaret Rae. |
| Contributors | Van Staden, Johannes. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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