The Sainsbury Orchid Conservation Project: Propagation for Conservation

Fifty orchid species are known in wild situations in the British Isles today. Approximately a third of these are thought to be threatened and ten species are protected under Schedule 8 of the Wildlife and Countryside Act (1981).

Several species have populations of less than one hundred individuals, and their natural distribution has been further disrupted in the last 50 years by changes in land use, including drainage of marshes and increased use of fertilisers. The rarest species must be the lady's slipper orchid (Cypripedium calceolus) which through over collection is now reduced to a single flowering individual. The fen orchid (Liparis loeselii) is severely threatened in both Britain and Europe due to the drainage of its habitat of dune slack and fen. One way of protecting wild orchids is to learn how to grow them well in cultivation and to propagate them in order to supplement and extend the natural populations.

The Sainsbury Orchid Conservation Project was initiated in 1983 at the Micropropagation Unit at the Royal Botanic Gardens, Kew with the generous backing of Sir Robert and Lady Sainsbury. The intention was to grow British and European orchids from seeds, using laboratory and greenhouse techniques, and then re-establish plants at safe sites in the wild.

Symbiotic propagation from seeds

Seeds are used in propagation, in preference to tissue culture, in order to maintain genetic diversity and because some seeds may be stored for later use. Orchid seeds are dust-like and consist of an embryo of only 100-200 cells within the seed coat. Unlike many other seeds, they contain very few food reserves (endosperm) to enable the seed to germinate. In orchid seeds, the nutrients required for germination are provided by a mycorrhizal fungus with which it forms an association. This can be mimicked in the laboratory by sowing sterilised seeds on agar plates containing ground oats and inoculating the plates with a culture of an appropriate fungus.

Fungal isolates are obtained by dissecting roots of actively growing orchid plants, a non-destructive process. The fungus is found as intracellular fungal coils (pelotons), linked via root hairs to the soil. The exact process of symbiosis is poorly understood, but it is thought that the fungus digests organic materials and that the resulting nutrients are transferred to the cells of the orchid by simple diffusion and digestion of the fungus by the orchid host. Following penetration of the seed-coat and embryo by the fungus, in the first stage of germination the seed-coat splits as the embryo expands to form a protocorm with rhizoids. The orchid seems to be able to control the rate of infection, and when protocorms are transferred to fresh medium, no further inoculum of fungus is required to sustain growth. The cultures are kept in the dark for germination and the early stages of protocorm development, and then moved into the light when the leaf shoots begin to turn green. Further development of plants from protocorms may be quite rapid. For example, the germination of seeds of the green-veined orchid (Orchis morio) can occur after 6 weeks and healthy green shoots are produced after 3 months. Plantlets of the autumn lady's tresses (Spiranthes spiralis) form tubers and are ready to wean into the glasshouse within a year of sowing if a symbiotic fungus is used. Plants of the fen orchid have been raised using a fungus from the Project's collection and planted out on former sites in the fens of Norfolk.

Asymbiotic propagation

Asymbiotic media have been developed using chemicals and plant extracts to imitate the nutrients supplied by the fungus. Germination on asymbiotic media can take several months, and years may be required for plants to reach a size comparable to that achieved in a few months using symbiotic methods.

No appropriate fungus has been found in the roots of the monkey orchid (Orchis simia), one of the plants protected by legislation in Britain. However several hundred seedlings have been raised by sowing the seeds on a nutrient medium.

A modification of this technique has been used for the lady's slipper orchid. Immature seeds from green capsules are sown, as trials with mature seed have been unsuccessful. The natural development of the Cypripedium shows an adaptation for survival in a cool climate and this is exploited in its propagation. The seeds are sown on media containing mineral salts and amino acids and then chilled. After a few months, protocorms form, which then develop roots and leaf buds. The first leaves are produced after a further period of chilling. Thousands of seedlings have now been raised from seeds of the British plant and are being planted at former sites. This is carried out in collaboration with the Species Recovery Programme of English Nature.

Elsewhere in Europe this species is more widespread and observations of these populations have been useful in selecting re-establishment sites. Plants in the Living Collection at Kew, of North American origin , are being used to investigate factors which influence germination.

Trial plantings

Pilot studies to establish seedlings in the wild have now begun with laboratory-raised seedlings of lady's slipper orchid, bee orchid (Ophrys apifera), marsh helleborine (Epipactis palustris), southern marsh orchid (Dactylorhiza praetermissa), fen orchid (Liparis loeselii) and two species of Orchis: the lax-flowered orchid (O. laxiflora) and the green-veined orchid (O. morio). The first trial was made in 1987 with the lax-flowered orchid. This species does not occur in mainland Britain, so seedlings may be easily recognised among other orchid species in the area. The plants are now well established at Wakehurst Place and have flowered every year since 1988. Plants grown from native seed from Jersey have been raised in the laboratory for a re-establishment project there. Seedlings of the spotted orchid (Dactylorhiza fuchsii) grown from seed collected at Wakehurst Place were added to the wild flower plantings there in 1989 and have flowered subsequently, as have symbiotically raised seedlings of the green-veined orchid planted out at both Kew and Wakehurst.

A few seedlings of marsh helleborine flowered within months of being planted out on the Rock Garden at Kew and the following year, almost every plant produced flowers which later formed seed capsules through natural pollination.

Southern marsh orchid seedlings raised symbiotically by the Project have been planted in the Loder Valley Reserve at Wakehurst Place as part of a postgraduate project to study the ecological requirements of orchid seedlings.

The most recent plantings have been in a habitat garden and natural sites controlled by English Nature and the National Trust. These plants are being closely monitored.

The project works in close collaboration with English Nature, various county Naturalists' Trusts and other conservation and land agencies who not only supply much of the seed but also the local expertise on sites suitable for re-introduction and establishment of plants.

Many of the rarer populations of orchids are at the edges of their natural ranges in the British Isles and their insect pollinators may not be present. They are watched over during their flowering season by volunteers who are trained to pollinate the plants while guarding them against theft. Some of the seeds are collected under licence for use by the Project.

The genetic integrity of plant material is a major concern when attempting this kind of work. Genetic fingerprinting is being carried out in the Jodrell Laboratory at Kew to ascertain whether those specimens of lady's slipper orchid in British Gardens come from the original native stock and their degree of genetic diversity. Similar studies are to be carried out on other threatened orchids.

A number of the methods developed by the Project could be used to raise some species in large numbers for introduction in gardens and public areas. Specialist nurseries are now starting to adopt the symbiotic technique to raise seedlings. Plants of horticultural merit, such as the Dactylorhizas, are becoming more widely available.

In summary, we are taking positive steps to conserve threatened orchids and their habitats, not only through re-establishing and augmenting the natural populations, but also by emphasising their educational, horticultural and amenity value.