Identification of the seasonal conditions required for dormancy break of Persoonia longifolia (Proteaceae), a species with a woody indehiscent endocarp.
The mechanisms involved in breaking seed dormancy in species with woody endocarps are poorly understood. In a landmark study examining the role of endocarps in regulating germination, our aim was to investigate the effects of the natural sequence of environmental conditions on dormancy break of a species with a woody endocarp (Persoonia longifolia).



The role of the endocarp in germination was investigated through imbibition and endocarp removal germination tests. The use of burial to break dormancy was examined and results from these experiments were used to guide laboratory investigations into the use of wet/dry cycling and stratification to break dormancy.



Endocarps were water-permeable. Germination increased from 0 to 92·5 % when endocarps were removed. During burial in the field and nursery, 41·6 and 63·7 % of the endocarps germinated, respectively, after 36 months. Ex situ post-burial germination was cyclical and highest after 30 months of burial (45·4 % nursery and 31·8 % field). Highest germination occurred in wet/dry trials when the dry summer was long (20 weeks), had fluctuating temperatures (30/50 °C) and two long (7 d) wet cycles and was followed by moist winters at 10/20 °C. A stratification trial found that highest germination occurred following incubation for 12 weeks at 30 °C (including 2 weeks moist) + 6 weeks moist at 8 °C then placement at 20/10 °C for germination.



Summer conditions break physiological dormancy of the embryo and promote opening of the endocarp, allowing seeds to germinate during winter conditions. By closely monitoring the environment that endocarps are exposed to in nature, dormancy breaking mechanisms can be identified and used to improve germination. These results outline for the first time how dormancy and germination are regulated in a species with a hard woody endocarp, insights which will significantly improve our understanding of other species with similar reproductive features.
Kings Park and Botanic Garden, West Perth, WA 6005, Australia School of Plant Biology, Faculty of Science, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia chia@wn.com.au.
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Chia
Bush Futures, 4 James Street, Guildford, WA 6055, Australia School of Agricultural and Resource Economics, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
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Sadler
Kings Park and Botanic Garden, West Perth, WA 6005, Australia School of Plant Biology, Faculty of Science, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
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Turner
Department of Biology, University of Kentucky, Lexington, KY 40506, USA Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY 40546, USA.
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Baskin
D018525:Germination / Q000502:physiology*; D057445:Plant Dormancy / Q000502:physiology; D039105:Proteaceae / Q000502:physiology*; D012621:Seasons; D012639:Seeds / Q000502:physiology; D014867:Water / Q000502:physiology; D014934:Wood
D014867:Water
Persoonia longifolia; burial; dormancy break; physiological dormancy; seed germination; stratification; wet/dry cycles; woody endocarp