In vitro propagation of Scilla natalensis planch.
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Date
1999
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Abstract
In South Africa, large quantities of Scilla natalensis are harvested from wild populations
and sold as traditional medicine, which is reducing the density, distribution and genetic
diversity of wild populations. The enforcement of existing legislation, however, has
proved ineffective with plants being traded locally and internationally. It has therefore,
been suggested that ex situ conservation through cultivation may alleviate pressures
on natural resources. Conventional propagation of these plants, however, is usually
fairly slow. In vitro propagation provides a rapid means of propagating selected
chemotypes or cultivars, serving both conservation and commercial interests.
In the first part of the study, continuous culture systems were established for the three
forms of Scilla natalensis, S. natalensis sensu stricto (Form A), S. natalensis syn. S.
kraussii (Form B) and S. natalensis syn. S. dracomontana (Form C). The efficiency of
the systems was strongly influenced by genetic factors, viz the form and epigenetic
factors, viz the explant type, carbohydrate source, plant growth regulators and gelling
agents. The form, Form A, Form B or Form C respectively, influenced shoot initiation
with the larger forms generally producing more shoots than the smaller forms (Form A
> Form B > Form C). The data confirmed that the three forms are significantly different
in terms of their physiological response to carbohydrates, plant growth regulators and
gelling agents in vitro. Since the effect of form could not be compensated for by the
addition of either carbohydrates, plant growth regulators or gelling agents, this may
provide some support for the reinstatement of these forms as three species, Scilla
natalensis Planch., S. kraussii Bak. and S. dracomontana Hilliard & Burtt. The explant
type, that is bulb or leaf explants respectively, significantly influenced shoot initiation.
Leaf explants generally produced more shoots than bulb explants. The carbohydrate
source significantly influenced shoot initiation. The explants generally produced more
shoots when cultured on media containing glucose or sucrose than on media containing
fructose, lactose, maltose and particularly mannitol. The combination of cytokinins and
auxins significantly influenced shoot initiation. Shoot initiation was higher for
combinations of kinetin: IAA than for combinations of kinetin: NAA or TDZ: NAA.
Optimal shoot initiation for Form A, Form B and Form C occurred on media containing
1 to 2 mg I-1 kinetin and 1 to 2 mg I-1 IAA. The gelling agent also influenced shoot
initiation with media solidified with Gelrite® producing more shoots than media solidified
with Oxoid or Unilab agar. Shoots were then rooted on media containing IAA, IBA or
NAA and the plantlets were successfully acclimatised. These continuous culture
systems can be used to produce large quantities of plantlets, which may alleviate
pressures on natural resources and provide an alternative source of high quality plants
for the burgeoning medicinal plant market.
In the second part of the study, the effect of carbohydrate source and concentration on
growth and development of shoots of S. natalensis syn. sensu stricto (Form A) were
determined. This has applications for the acclimatisation and germplasm storage of
bulbous plants. The carbohydrate source and concentration significantly influenced the
growth and development of shoots. In the absence of carbohydrates, the shoots were
short with spindly leaves and short roots. When media were supplemented with high
concentrations of fructose, the shoots were long with broad leaves, small bulbs, and
few short to medium length roots at low concentrations. At higher fructose
concentrations, however, the shoots were robust and short with narrow, sometimes
deformed leaves, large bulbs, and few stunted, brown roots. When sucrose was
substituted for fructose, the shoots were robust and long with narrow and often red-pigmented
leaves, large bulbs, and many long, thick roots. When AC was used in
combination with sucrose, however, the shoots were robust and short with few, and
occasionally red-pigmented leaves, small to medium bulbs, and few, severely stunted
roots. Optimal shoot growth and development in terms of shoot weight (FW) and quality
occurred on media containing glucose or sucrose (40 to 60 g I-1). The carbohydrate
source and concentration also significantly influenced the physical properties of media
particularly pH, electrical conductivity (EC) and gel-strength. The pH decreased slightly
with increasing glucose concentration but decreased significantly with increasing
fructose concentration when fructose was used alone or in combination with glucose.
The pH also decreased significantly with increasing sucrose concentrations when
sucrose was used in combination with Sigma AC. The EC decreased significantly with
increasing fructose concentration when fructose was used alone but remained fairly
constant irrespective of glucose concentration when glucose was used alone or in
combination with fructose. The EC also remained fairly constant irrespective of the
sucrose concentration but decreased with increasing sucrose concentration when used
in combination with AC. The gel-strength remained fairly constant irrespective of
glucose. The gel-strength decreased with increasing fructose concentration when used
alone or in combination with glucose. The gel-strength of media increased with
increasing sucrose concentration although the addition of Sigma AC significantly
decreased the gel-strength of media, which decreased with increasing sucrose
concentration. The brand and concentration of AC also influenced gel-strength. The
matrix plot suggested that the effect of carbohydrate source and concentration on the
growth of shoots may be largely due to the indirect effects of these physical properties
such as hydrolysis of carbohydrates, the spectrum and quantity of the breakdown
products and the availability of nutrients, plant growth regulators and water rather than
the direct effects of pH, EC and gel-strength per se.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1999.
Keywords
Scilla Natalensis--Micropropagation., Plant Micropropagation., Theses--Botany.