Dormancy release in seeds of Lolium rigidum Gaud. (annual ryegrass) was investigated in relation to temperature and seed water content. Freshly matured seeds were collected from cropping fields at Wongan Hills and Merredin, Western Australia. Seeds from Wongan Hills were equilibrated to water contents between 6 and 18% dry weight and after-ripened at constant temperatures between 9 and 50°C for up to 23 weeks. Wongan Hills and Merredin seeds at water contents between 7 and 17% were also after-ripened in full sun or shade conditions. Dormancy was tested at regular intervals during after-ripening by germinating seeds on agar at 12-h alternating 15°C (dark) and 25°C (light) periods.Rate of dormancy release for Wongan Hills seeds was a positive linear function of after-ripening temperature above a base temperature (Tb) of 5.4°C. A thermal after-ripening time model for dormancy loss accounting for seed moisture in the range 6–18% was developed using germination data for Wongan Hills seeds after-ripened at constant temperatures. The model accurately predicted dormancy release for Wongan Hills seeds after-ripened under naturally fluctuating temperatures. Seeds from Merredin responded similarly but had lower dormancy at collection and a faster rate of dormancy release in seeds below 9% water content.
The quality of seed-conservation collections, and hence their value for species reintroduction or restoration, is critically dependent on factors operating in the period between the point of collection and arrival at environmentally controlled processing and storage facilities. The timing of the acquisition of desiccation tolerance and seed longevity in air-dry storage, in relation to mass maturity and the time of natural seed dispersal, varies across species. In some wild plant species, seed quality continues to improve up to, and possibly beyond, the point of dispersal. Holding immature berries of Solanum dulcamara L. and capsules of Digitalis purpurea L. under natural conditions enabled comparison of seed quality between seeds stored under natural conditions and those dried rapidly under seedbank dry-room conditions. While seeds from fully ripe (post-mature) capsules of D. purpurea were insensitive to different post-harvest drying treatments, seed quality declined when mature berries of S. dulcamara were held under natural conditions. These results emphasise that the selection of post-harvest treatment will not only depend on the maturity of collected seeds but also may vary across species depending on the fruit type. Except for subtropical and tropical coastal locations, ambient daytime conditions during the main seed-collecting season (November–February) across Australia can be expected to result in tolerable rates of seed deterioration for the duration of seed-collecting missions. However, because seed moisture levels can be considerably higher than when equilibrated with ambient relative humidity, post-harvest handling decisions should ideally be informed by measurements of seed moisture at the time of collection, and subsequently seed moisture should be monitored during transit.
Ex situ seed conservation aims to support species survival in the wild. This can be achieved by contributing genetic material for reintroduction. The goals of reintroduction are to increase both plant and population numbers, create self-sustaining populations and ultimately remove a species from its threatened listing. Quality seed collections with a broad genetic base are required to achieve this goal. Storage conditions that minimise deterioration of seeds will maximise the quality of seeds available for future use. Additionally, ex situ seed conservation provides long-term insurance against species or genotype loss until actual or potential threats can be removed. As threats to biodiversity escalate the most judicious conservation strategies will be ones that combine available resources to provide the highest possible degree of protection. Banked seeds are available irrespective of season and periods of low fecundity. Forward planning of reintroduction projects can be achieved with knowledge of the quantity and quality of banked seed. This paper discusses the challenges facing ex situ seed conservation while highlighting the benefits of integrating ex situ seed storage and plant reintroduction to help provide for better conservation outcomes.
Ecological restoration of grassy woodland ecosystems is now a significant landscape‐scale conservation objective throughout southern Australia. Technological improvements in direct seeding are now sufficiently well‐advanced to examine whether cost‐effective restoration of grassy woodlands is feasible. Consideration of six ‘best practice case studies shows substantial evidence of success. Further refinement of direct seeding techniques, in combination with native seed production systems, however, will be required into the future to meet the scale of woodland conservation targets and restore ecological function.
The effect of hydration (priming) treatment on dormancy release in annual ryegrass seeds from two populations was investigated. Hydration duration, number, and timing with respect to after-ripening were compared in an experiment involving 15 treatment regimens for 12 wk. Seeds were hydrated at 100% relative humidity for 0, 2, or 10 d at Weeks 1, 6, or 12 of after-ripening. Dormancy status was assessed after each hydration treatment by measuring seed germination at 12-hourly alternating 25/15 C (light/dark) periods using seeds directly from the hydration treatment and seeds subjected to 4 d postpriming desiccation. Seeds exposed to one or more hydration events during the 12 wk were less dormant than seeds that remained dry throughout after-ripening. The longer hydration of 10 d promoted greater dormancy loss than either a 2-d hydration or no hydration. For the seed lot that was most dormant at the start of the experiment, two or three rather than one hydration event or a hydration event earlier rather than later during after-ripening promoted greater dormancy release. These effects were not significant for the less-dormant seed lot. For both seed lots, the effect of a single hydration for 2 d at Week 1 or 6 of after-ripening was not manifested until the test at Week 12 of the experiment, suggesting that the hydration events alter the rate of dormancy release during subsequent after-ripening. A hydrothermal priming time model, usually used for modeling the effect of priming on germination rate of nondormant seeds, was successfully applied to dormancy release resulting from the hydration treatments.
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