Ex situ conservation of orchid seeds of the Lycaste genus : a thesis presented in partial fulfilment of the requirements for the degree of Master of Sciences in Plant Breeding at Massey University, (Manawatū campus) Palmerston North, New Zealand
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Date
2022
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Massey University
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Abstract
The orchid family (Orchidaceae) is the second largest family in the plant kingdom with about 28000 species. Most orchid species are endangered. Both in situ and ex situ approaches are necessary for the conservation of endangered and threatened species, including orchids. In situ conservation should be the priority, however, ex situ conservation can complement initiatives to ensure species survival in situ. More information on orchid seed dispersal mechanisms, pollination, and germination biology is needed to support conservation efforts. This study included three endangered species from Mesoamerica, Lycaste virginlis, L. cochleata, and L. lasioglossa that should be considered a high conservation priority. The primary intention of the different experiments was to contribute information that favours seed conservation of endangered orchid species from the Mesoamerica biodiversity hotspot. For this, characterization of the seed capsule morphology and seed micro-morphological traits were investigated followed by the assessment of the effect of three media on in vitro asymbiotic seed germination and the viability and germination of the seeds under different storage conditions. The qualitative traits of the seed capsules and the seeds were similar in appearance and colour for the three Lycaste species evaluated. However, high variability was found in the quantitative traits of both seed capsules and seeds. Based on the micro-morphological traits’ findings, it is possible to speculate that these three epiphytic Lycaste species which all grow under dense tropical canopies are dispersed by water drops falling onto the orchid plant from the canopy and by gravity. This suggestion is consistent with their having small-sized seeds, relatively large embryos, and low air volume (in comparison with other epiphytic and terrestrial orchid species). Specifically, those traits may allow the seeds to be dispersed in vegetation-dense and humid natural environments. Further research needs to be done to validate these findings, including more species of the Lycaste genus. For the successful implementation of conservation plans, it is important to understand the specific nutritional requirements for seed germination of the target species. This study assessed three different germination media (Murashige and Skoog (MS), Knudson C, and terrestrial orchid medium BM-1) to identify the most suitable one for asymbiotic in vitro germination. The germination percentages and seedling development significantly varied across the three Lycaste species. MS media sustained the highest germination percentages with high-quality plantlets (in stage 4). Still, germination did not reach the potential suggested by the tetrazolium test for viability, meaning that further media optimization is required. Knudson C media was also a good option for the seed germination and seedling development for two of the three species (L. cochleata and L. lasioglossa). The effect of different storage conditions (temperature, RH, and time) on seed viability and germinability was tested. The differential scanning calorimetry (DSC) method was used to identify each species' lipid melting and crystallization points. Based on the DSC findings, storage temperatures below -75°C is recommended for the storage of three Lycaste species. Still, further research needs to be done by testing more and different storage temperatures to validate these findings.
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orchid, epiphytic, tropical, seed morphology, micro-morphology, air space volume, viability, asymbiotic in vitro germination, cryopreservation, ex situ conservation, seedling development