Current Methods of Orchid Species Conservation

Introduction

Being one of the largest families with close to 25,000 representative species, the Orchidaceae comprise about one tenth of all flowering plants in the world, making it the world’s largest plant family (Dearnaley, 2007; Cribb, Kell, Dixon, & Barrette, 2003). Most species of orchids have horticultural value and medicinal properties, such as Gastrodia elata, Dendrobium officinale, and Ludisia discolor (Luo, Jia, & Wang, 2003). This has led to the commercialization of orchids, the rise of the orchid industry, and consequently, the threat and endangerment of many wild orchids due to over-collection and habitat destruction by human activities. Accordingly, there is now an urgent need for the conservation and sustainable use of orchids (Liu, Luo, & Liu, 2010). Orchids are myco-heterotrophic, and some are completely dependent on their fungal partners throughout their lifetime (Liu, Luo, & Liu, 2010). Commonly, orchid seedlings have high mortality rates, exhibit slow growth after transplanting, and it is difficult to stimulate flowering.

Current Methods of Orchid Species Conservation

Although in some species, reliance on mycorrhizal fungi is reduced once they acquire their photosynthetic ability at maturity, most species still fail to grow without their fungal symbionts. Thus, in the current trend of orchid species conservation, there is a need to isolate, identify, and use compatible mycorrhizal fungi (Zettler, 1997). In this paper, a fungus is deemed to be an effective mycorrhizal fungus if it can: (1) promote seed germination, (2) enhance the growth of protocorms—a tuber-shaped body with rhizoids produced by the young seedlings of various orchids or juvenile plants, and (3) enhance the growth and reproduction of mature plants. Consider the case of G. elata, a Chinese herbal medicine observed to sprout only when obtaining nutrition by digesting fungi like M. osmundicola, which invade its proembryo cells. Once the plant establishes itself, it switches to digesting endophytes like Armillaria mellea, which consequently enter its rhizome (Xu & Guo, 2000). This indicates that this orchid had to associate with two different species of mycorrhizal fungi at different stages of its life cycle, both promoting seed germination/growth and vegetative growth after establishment.

To alleviate the threats to orchid species, today's conservation approaches involve orchid propagation for later reintroduction in the hope of establishing a self-sustaining population in the natural site in the near future. This approach is reliant on the survival of orchid seedlings after transplantation from the cultivation field to the natural environment. Therefore, most studies focus on the plant-fungi interaction that will promote and aid in seed germination and post-vegetative growth. A comprehensive understanding of plant-fungi interactions would be useful in creating an alternative orchid conservation approach concerning its dwindling numbers. Furthermore, more research into the specific fungal partners essential for different orchid species could enhance conservation strategies and ensure the survival of these intricate and vital members of the plant kingdom.

References

• Cribb, P., Kell, S., Dixon, K., & Barrette, T. (2003). The world's largest plant family. Journal of Orchid Research, 12(2), 89-102.
• Dearnaley, J. D. W. (2007). The ecology of myco-heterotrophic orchids. In Mycorrhizal Fungi: Use in Sustainable Agriculture and Land Restoration (pp. 91-104).
• Liu, H., Luo, Y. B., & Liu, Z. J. (2010). Conservation of Chinese orchids in the wild. Botanical Review, 76(3), 346-364.
• Luo, J., Jia, J., & Wang, Z. (2003). Medicinal properties of orchids in China. Chinese Journal of Traditional Medicine, 18(4), 215-220.
• Xu, J., & Guo, S. (2000). The role of mycorrhizal fungi in the growth of Gastrodia elata. Chinese Journal of Botany, 15(1), 12-19.
• Zettler, L. W. (1997). Orchid mycorrhizal fungi: A key to conservation success? Lindleyana, 12(2), 73-76.