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Orchid – mycorrhiza relationships, propagation of terrestrial and epiphytic orchids from seed

Hughes, Oliver Thomas Wesley (2018) Orchid – mycorrhiza relationships, propagation of terrestrial and epiphytic orchids from seed. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Many orchids are rare and endangered due to habitat loss, degradation and human interference. This thesis aims to improve our understanding of orchid-mycorrhiza relationships and optimise methods for successful in vitro germination and development of terrestrial and epiphytic orchids. The research undertaken advances our understanding of orchids and has applications for conservation and horticulture. Fungal specificity plays a key role in orchid distribution and the colonisation of habitats. This was investigated in the Australian terrestrial orchid, Microtis media R. Br. in Chapter 2. Experiments demonstrated low fungal specificity in germination in vitro, although later development was more specific, with one fungus inducing protocorm development through to adult plants. Fungal compatibility was tested in several Eurasian terrestrial orchids in Chapter 3. Varying degrees of specificity were observed, with Anacamptis morio (L.) R.M.Bateman, Pridgeon & M.W.Chase and Dactylorhiza incarnata (L.) Soό displaying low fungal specificity whereas Serapias spp. were more specific. Orchids are commonly propagated without fungi using asymbiotic media. Asymbiotic and symbiotic methods were compared in two Eurasian terrestrial orchids in Chapter 4. In both cases, symbiotic methods resulted in higher germination and development. In Anacamptis laxiflora (Lam.) R. M. Bateman, Pridgeon & M. W. Chase, successful seedling establishment ex vitro was only achieved with symbiotic seedlings. Following this study, the effect of substrate rugosity and complexity on germination in asymbiotic and symbiotic culture of two Eurasian terrestrial orchids was investigated in Chapter 5. Substrate rugosity had a positive effect on germination and development in symbiotic cultures of A. morio and both asymbiotic and symbiotic cultures of Dactylorhiza purpurella (T.Stephenson & T.A.Stephenson) Soó. The subtribe Pleurothallidinae is one of the largest in the Orchidaceae and little is known about their propagation requirements. A number species from different genera within this group were tested with different asymbiotic media and fungi isolated from plants in an ex situ collection in Chapter 6. Germination was highest with two fungal strains but development of plantlets only occurred on asymbiotic media. Ex situ study and propagation of myco-heterotrophic orchids poses some difficulties. A novel method is presented, using microcosms for the initiation of tripartite symbioses with tree seedlings, fungi and orchids in Chapter 7. Associations between tree seedlings, fungi and orchid seed were observed. Germination was not achieved with seed of Neottia nidus-avis (L.) Rich. The method provides a basis for further development with applications in a range of ecological studies.

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