Eucalyptus trees are a significant source of fuelwood, timber and raw material for the
paper and pulp industry. In South Africa, Eucalyptus grandis and its hybrids are in high
demand due to their fast growth and suitability of their timber for a wide range of
products. Breeding and selection for superior quality eucalypts could sustain this high
demand through selection and subsequent multiplication of superior genotypes and their
use in controlled crosses. However, for this to be successful, a wide genepool must be
available and maintained. Germplasm conservation of both vegetative and sexual
material is therefore an integral part of such activities. However, in the case of trees, in
vivo conservation practices are expensive and hazardous. The aim of this project was
therefore to establish alternative conservation strategies for short-to-medium and long-term
use of Eucalyptus spp. to facilitate on-going breeding and clonal programmes.
For short-to-medium term storage, shoot cultures were subjected to various minimal
growth conditions. Of the investigated treatments, reducing nutrients was the best storage
method and shoots were maintained for 10 months with multiplication rates of 13.75 ±
7.05 shoots/explant. Encapsulated axillary buds were stored in jars at 10 °C or 28 °C. Of
these two treatments, viability was sustained for longer (6 months) at 4 °C.
Before establishing pollen storage regimes, viability assessment methods were evaluated
and these consisted of in vitro germination on a BK (Brewbaker and Kwack, 1963)
medium for 24 hours (26 ± 3.0%) and staining with two tetrazolium salts. Medium-term
storage of pollen was best achieved by maintenance in the fridge (4 °C) without any
desiccating substance (8 months at 6.73 ± 1.21%).
Cryopreservation protocols were investigated for axillary buds and pollen. Buds that were
2 mm long were pretreated with chemical cryoprotectants, and a mixture of DMSO
(dimethylsulphoxide) and glycerol was found to induce high survival rates (63%) after
washing with MS (Murashige and Skoog, 1962) and 4 g.l-1 sucrose solution. Explants
precultured in 1M sucrose showed increased tolerance (explant retained high survival
rates of 80%) when desiccated to 20% moisture content fresh weight basis (fwb).
Although pretreatments were successfully established, explants did not survive storage in
liquid nitrogen indicating the need for further optimization of protocols. Pollen was
successfully cryopreserved for 12 months with 23% survival rates.
Applications and future research strategies of the developed protocols to Eucalyptus
breeding programmes are discussed. / Thesis (M.Sc.)-University of Natal, Durban, 1998.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/4695 |
| Date | January 1998 |
| Creators | Thokoane, Novungayo Lucy. |
| Contributors | Watt, M. Paula., Mycock, David John. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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