Comparison of seed traits of tropical (Indonesia) and temperate (New Zealand) orchid species to support orchid seed conservation : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Horticultural and Agricultural Science at Massey University, Palmerston North, New Zealand
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Date
2020
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Massey University
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Abstract
Most orchid species are endangered, and a basic understanding of their seed biology is required to support conservation efforts. In particular, more knowledge of orchid seed characteristics would be useful for both in situ and ex situ conservation. This comparative study used morphological and biochemical approaches to characterise and compare orchid seed qualitative and quantitative traits, to explore biochemical changes during natural seed ageing and to investigate different asymbiotic in vitro seed germination media and cryopreservation techniques for ex situ conservation. This study included six orchid species with different growth habits and distribution ranges (Dendrobium strebloceras, D. lineale, D. cunninghamii (epiphytic), Gastrodia cunnninghamii, Pterostylis banksii and Thelymitra nervosa (terrestrial)) from temperate New Zealand and tropical Indonesia.
Morphometric analyses revealed similarities in the qualitative traits of seeds and capsules at the genus level (Dendrobium). However, high variability in micro-morphological seed characteristics were observed in the orchid species in this study which were unrelated to their taxonomy, biogeographical origin, or growth habit, suggesting different ecological adaptations possibly reflecting different modes of dispersal.
An investigation of the seed fatty acids showed that linoleic, oleic and palmitic acids (polyunsaturated, monounsaturated and saturated fatty acids, respectively) were the most abundant fatty acids in the seeds of all species and that rapid degradation of unsaturated acids occurred during ageing. Three epiphytic Dendrobium species had similar lipid composition but Gastrodia cunnninghamii, Pterostylis banksii and Thelymitra nervosa (terrestrial species) were characterised by the absence of erucic and palmitoleic acid. Changes in the proportion of oleic and linolenic acid were strongly correlated with seed viability loss. The ageing pattern was species-specific with D. strebloceras being more vulnerable to lipid degradation.
Epiphytic Dendrobium orchids had a less stringent media formulation requirement for seed growth than terrestrial orchids, and similarly, seeds of tropical species D. lineale and D. strebloceras germinated more easily than those of temperate species in this study. Cryopreservation with direct immersion of dry orchid seeds in liquid nitrogen is suggested as the most effective and efficient method for orchid seed conservation.
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Orchids, Seeds, Indonesia, New Zealand, Conservation