Gladiolus scabridus - the road to conservation and commercialisation.
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Date
2005
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Abstract
There is at present a growing concern and awareness of the endangered status of many
indigenous South African plants in the wild, a number of which have potential for commercial
production. One such example is Gladiolus scabridus, a vulnerable species endemic to the
mountains of northern KwaZulu-Natal and southern Swaziland. It has considerable potential
due to its floral characteristics. However, little is known about its horticultural requirements.
Thus propagation and cultural practices were investigated with the aim of both conservation
and commercialisation of the species.
The ideal conditions for G. scabridus seed germination were determined. The presence or
absence of light had no significant effect. Optimum germination was achieved at 20 QC of
both winged and dewinged seeds. Higher temperatures appear to have a negative effect on
germination and none of the winged seeds germinated at 30 QC. Under ideal conditions, fresh
seed showed significantly higher vigour and viability than stored seed although the
germination of stored seed was hampered by a higher internal fungal content.
Successful tissue culture protocol was established for G. scabridus axillary bud and cormel
halve explants. During the initial shoot initiation and proliferation stages (stage I and 11), the
significantly higher shoot numbers occurred in the absence of growth regulators in both
explant types. However, shoots with 1.0 mg 1 -1 6-benzyl-amino-purine (BAP) and 0.5 mg 1 -1
1-naphthalene-acetic-acid (NAA) were healthier in appearance. Higher levels of 5.0 mg 1 -1
NAA inhibited shoot production and encouraged root development in cormel halve explants.
During stage 11, axillary bud explants showed root and cormlet development. More roots were
initiated without growth regulators, whilst 5.0 mg 1 -1 NAA resulted in significantly better
cormlet development. Shoot and cormlet growth of cormel halve explants during stage II was
not significantly affected by the presence or absence of NAA and BAP. Significantly more
roots were produced with 5.0 mg 1 -1 NAA. During stage III (rooting), the presence of activated
charcoal (AC) was essential for the initiation and development of roots in vitro. Root and
cormlet development in all explant types was significantly affected by the interaction between
the previous treatments from stages I and 11 and the new treatments. During stage IV
(hardening off) , most explants died down in the hardening off media leaving resting cormlets.
There was a significant interaction between 1.0 mg 1 -1 NAA and 0.3 % AC from stage III,
resulting in significantly more cormlets in both axillary bud and cormel halve explants. There
was successful cormlet growth after cold storage which is advantageous in reducing the need
for acclimatization. G. scabridus corms were successfully forced out of their normal flowering period.
Temperatures of 10,5.5 and 2 QC showed successful corm initiation although the corms need
to be stored for longer at warmer temperatures. It is suggested that a treatment of 2 QC for
6 weeks is the optimal condition for forcing G. scabridus corms.
Although originating from a stressful environment, G. scabridus appears to show capacities
for improved growth under controlled conditions. Fertilizer applications enhanced growth and
reduced the time to flowering. Nitrogen (N) was found to be important for vegetative growth,
flowering and daughter corm development, whereas potassium (K) influenced cormel
production. Fertilizer with higher N and lower K is appropriate for the beginning and middle
of the growing season and then adjusted to a lower N and higher K fertilizer to promote
cormel formation. G. scabridus was found to produce prolific numbers of cormels which is
an important source of plant material. Mineral leaf analysis showed that optimum levels for
wild species are lower than those for hybrid gladioli with the optimum levels affected by
physiological corm maturity and subsequent plant growth.
Norms for postharvest handling of cut G. scabridus spikes have been developed. Spikes held
in 2 % sucrose had a longer vase life and better floret opening and quality than those kept
in distilled water, Prolong,
Chrysal, 2 % sucrose and 2 % ethanol, 1 % sucrose, 4 %
sucrose, 1 % sucrose and 0.5 % JIK, 2 % sucrose and 0.5 % JIK and 4 % sucrose and 0.5
% JIK, 2 % fructose and 2 % glucose. The use of commercially available solutions should
be used with caution. Florets produced a climacteric-like CO2 peak, but levels of ethylene
were unmeasurable. Cold storage and the use of polypropylene sleeves delays senescence.
G. scabridus spikes secrete droplets of a sticky substance which was confirmed to be extra
floral nectar through HPLC analysis. Market research revealed a positive response to the
species from consumers and retailers alike with potential for cultivation as a cut flower and
bedding plant. However, the cost will determine supply and demand.
A field study conducted at Bivane Dam, northern KwaZulu-Natal, confirmed that G. scabridus
colonies prevail in rocky, quartzite outcrops where they become wedged between the rocks.
Plants were found at different stages of development with populations of not more than 108
plants per colony. Soil data of G. scabridus sites was compared to that of two sites nearby.
It was found that G. scabridus soils are higher in phosphorus (P), zinc (Zn) and organic
carbon. Leaf analysis confirmed that they have adapted their growth to low nutrient levels.
The G. scabridus studies have clearly shown that the species can be successfully moved
from a wild plant to a commercially viable one and in so doing its conservation status can
also be improved.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
Keywords
Gladiolus--KwaZulu-Natal., Gladiolus--South Africa., Gladiolus--KwaZulu-Natal--Growth., Gladiolus--Physiology--KwaZulu-Natal., Gladiolus--Conservation--KwaZulu-Natal., Gladiolus--Propagation--KwaZulu-Natal., Gladiolus--Postharvest physiology--KwaZulu-Natal., Gladiolus--Postharvest technology--KwaZulu-Natal., Cut flowers--KwaZulu-Natal--Marketing., Endemic plants--KwaZulu-Natal., Theses--Horticultural science.