M. A. Weatherhead
Department of Ecology & Biodiversity, University of Hong Kong, Pokfulam Road, Hong Kong.
The work being carried out at the tissue culture unit in the Department of Botany, University of Hong Kong is described. Virtually all indigenous plants in Hong Kong are endangered by increasing urbanisation, illegal collection for herbal medicine and destructive hill fires. Thus we aim to conserve those species which are particularly rare and under greatest threat.
The tissue culture unit was set up in 1984 with the initial aim of propagation and conservation of the local wild orchid species. There are some 120 species of orchids in Hong Kong, 70% epiphytic and 30% terrestrial. 30 of these species have not been recorded from other locations but it is reasonable to assume that these could be found in adjacent areas of S. China where the topography and climate are similar to that of Hong Kong. This research programme has been remarkably successful in achieving seed germination, development of micropropagation techniques, study of some orchid mycorrhizas, seed storage and transfer of plants back to natural conditions.
Following the establishment of the orchid research programme, local interests led us to diversify research into other plants, the most significant of which are the three indigenous local Camellia species. We have also carried out investigations on the germination of Hibiscus seeds. This genus is not native to Hong Kong, but forms a large and decorative part of the local flora. Current research also includes studies on micropropagation of local bamboo species and assessment of their economic value.
Our resources are considerable given the lack of space in this crowded colony. Within the University we have a growth room, two laminar air flow cabinets and all the other ancillary equipment necessary. Additionally at the Kadoorie Agricultural Research Centre located in the New Territories, we have duplicate resources, with the addition of large greenhouses and extensive land for field experiments. At the Kadoorie Agricultural
Aid Association Botanic Garden, also in the New Territories, we have access to such facilities as replanting areas and collection opportunities for rare species conserved there.
Research on orchid conservation comprises the bulk of our research efforts. In terms of seed germination we have germinated more than 50% of the local species (Yam and Weatherhead, 1988, Tsui and Weatherhead, 1993). This has involved the formulation of new, chemically defined media both for initial sowing and subculture. Similarly, transfer of plantlets to natural conditions has been and is successful. The composition of suitable growing composts was greatly aided by a soil survey of many sites by Yam (1989). For the past few years we have been concentrating on developing techniques for "non-destructive" methods of micropropagating our wild orchids - that is to say using leaf tips, root tips or other organs as explants thus preserving the integrity of the mother plants. Such methods were pioneered by Goh and Tan (1979) in Singapore for the multiplication of commercial orchid hybrids, but it is our belief that we are one of the few laboratories worldwide who are refining these methods for use with wild orchids. Much of this work has been published (Yam and Weatherhead, 1987, 1990a, 1990b, 1990c, 1991a and 1991b; Nam and Weatherhead, 1993).
We have also set up an orchid seed bank and currently have some 60 species held at either 4oC or -196oC. Detailed studies have been carried out on the effects of humidity, temperature and storage period on the viability of 11 species. These results have been presented by Tsui and Weatherhead (1992) and Tsui (1992). Moisture content of the seeds was the most important factor for successful storage.
Fungal symbionts have been isolated from several species and grown in symbiotic culture with seeds and seedlings of the host plants and other species. The mycorrhizal fungi seem to be largely imperfect stages of Rhizoctonia spp. and thus far, there is no evidence of a specific relationship between the host plant and the fungus.
The three Camellia spp. native to Hong Kong (C. crapnelliana, C. granthamiana and C. hongkongensis) are all under threat of extinction. However, they can be micropropagated by axillary shoot induction from node and shoot tip explants. They can also be propagated by in vitro seed germination, but seed viability is short lived and seeds must be sown within 3-4 weeks of maturation (Siu, 1992).
There are some 57 species of bamboo in Hong Kong and more in China. In addition to horticultural value, they provide food, raw material, shelter and medicine (Cheong-Leen, 1985). There are many compelling reasons for mass propagation of the most desirable species, but it is not an easy plant to micropropagate. Our studies on this subject are at an early stage but we can report a moderate degree of success in the initiation of cultures from young nodal material.
Hibiscus seeds cannot be germinated easily and any resultant seedlings are extremely susceptible to fungal infection. At the request of a Hibiscus breeder in the USA, we developed a method for germination which effectively eliminates all of the problems. Sterilised seeds must first be nicked. They are then cultured in sterile vermiculite until plantlets emerge and, when large enough these are transferred to conventional compost.
Cheong-Leen H. (1985) In Hong Kong Bamboos by But P. H., Chia L. C., Fung H. L. Hu S. Y., Hong Kong Urban Council.
Goh C. J. & Tan H. (1979) Clonal propagation from leaf explants in an orchid hybrid Renantanda ammani. Plant Physiol. 63 (5 suppl.):116.
Nam K. S. & Weatherhead M. A. (1994) Conservation of Hong Kong native orchids by leaf tip culture. Proc. 14th World Orchid Congress, Glasgow, UK.
Siu L. P. (1992) Conservation and in vitro propagation of Hong Kong camellias. M.Phil. Thesis, Univ. of Hong Kong.
Tsui Y. C. (1992) Conservation and propagation of wild orchids in Hong Kong. M.Phil. Thesis, Univ. of Hong Kong.
Tsui Y. C. & Weatherhead M. A. (1992) Seed storage of some native orchids of Hong Kong. Proc. 4th Asian Pacific Orchid Congress, Chiang Mai, Thailand.
Tsui Y. C. & Weatherhead M. A. (1993) Germination and seedling development of some Hong Kong orchids. II. Submitted to Lindleyana.
Yam T. W. (1989) Conservation, ecology and propagation of the wild orchids of Hong Kong. Ph.D. Thesis, Univ. of Hong Kong.
Yam T. W. & Weatherhead M. A. (1987) Aspects of orchid conservation in Hong Kong. J. Orchid Soc. India. 1:81-84.
Yam T. W. & Weatherhead M. A. (1988) Germination and seedling development of some Hong Kong orchids. I. Lindleyana. 3:156-160.
Yam T. W. & Weatherhead M. A. (1990a) Early growth of seedlings of Hetaeria cristata and plantlet initiation from rhizome nodes. Lindleyana. 5:199-203.
Yam T. W. & Weatherhead M. A. (1990b) Nodal culture of some wild orchids of Hong Kong. Lindleyana.5:218-223.
Yam T. W. & Weatherhead M. A. (1990c) Conservation of native orchids in Hong Kong through repopulation. Proc. 13th World Orchid Congress, Auckland, New Zealand. 263-265.
Yam T. W. & Weatherhead M. A. (1991a) Leaf tip culture of several native orchids of Hong Kong. Lindleyana. 6:147-150.
Yam T. W. & Weatherhead M. A. (1991b) Root tip culture of several native orchids of Hong Kong. Lindleyana. 6:151-153.