Specialization in mycorrhiza of orchids across temperate Australian terrestrial orchid genera

A project undertaken at the Royal Tasmanian Botanic Gardens, and supervised by Nigel Swarts

Collaborators

Magali Wright, NRM South Tasmania; Ryan Phillips, Botanic Gardens and Parks Authority, Western Australia; and Mark Clements, CSIRO Plant Industry, Canberra.

Summary

Australia  has one of the most threatened terrestrial orchid floras with over 165 species listed on the EPBC act. The unique diversity in the Australian Orchidaceae and subsequent high levels of threat make studies into their biology and ecology a high priority from both evolutionary and conservation perspectives. Orchids rely on mycorrhizal associations to facilitate seed germination and growth. This is an obligate interaction for orchids since their minute dust-like seeds do not contain sufficient stored nutrition for development of the embryo. The orchid-mycorrhizal association is essential to facilitate uptake of soil nutrient and water to the germinating seed and subsequent developing plant. In temperate terrestrial orchids, the association extends to adulthood, where mature plants retain mycorrhizal associations to varying degrees of infection and nutritional dependency. The highly specific relationships with obligate fungal partners are a possible driving force in both the diversification and rarity in orchids.

This research brings together collaborators from across Australia to elucidate the influence of mycorrhizal specialisation on orchid diversity and habitat preference, distribution and rarity across the full phylogenetic breadth of Australia's temperate terrestrial orchid flora. Mycorrhizal fungi will be isolated from mature orchid plants and grown in culture for DNA sequencing.  ITS and nLSU sequencing data will be used to determine fungal diversity among key families Tulasnellaceae, Sebacinaceae and Ceratobasidiaceae known to associate with Australian terrestrial orchids.

Key questions that will be asked include the following:

  1. Is orchid diversity correlated with mycorrhizal diversity? Using a phylogenetic approach, we will assess the evolutionary trends in mycorrhizal associations and specificity across southern Australian terrestrial genera.
  2. Do orchid mycorrhizal colonisation patterns influence mycorrhizal diversity or specificity? We will investigate the relationship between underground morphology and mycorrhizal diversity/specificity of Australian terrestrial genera.
  3. Do mycorrhizal affiliations differ among orchids with differing habitat preference? We aim to determine how mycorrhizal diversity/specificity is partitioned across the geographic range and/or habitat preferences of Australia's terrestrial orchids.
  4. Does mycorrhizal diversity influence orchid diversification and speciation? With the information obtained from the first the three questions, we will investigate the influence of mycorrhizal diversity on orchid diversification.
Publication

Phillips, R.D., Barrett, M.D., Dalziel, E.L., Dixon, K.W. and Swarts, N.D. (2016). Geographical range and host breadth of Sebacina orchid mycorrhizal fungi associating with Caladenia in south-western Australia. Botanical Journal of the Linnean Society, 182, 140-151.

 
Figure 1. Glossodia major

Figure 2. Calochilus paludosis

Figure 3. Caladenia clavigera