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Preharvest sprouting (PHS), the germination of seeds on the maternal plant before harvest, is a big challenge for barley producers worldwide. It is attributed mainly to low seed dormancy. The balance between two classical plant hormones, gibberellin (GA) and abscisic acid (ABA) regulates seed dormancy and germination, and the endogenous level of these two hormones in plants is determined by their biosynthesis and catabolism. This thesis characterized the expression patterns of the major GA and ABA metabolism genes in barley cv. Betzes during seed development, and germination in both dormant and non-dormant seeds. The results indicate that specific gene family members of the two hormones play distinct temporal roles in regulating seed development, dormancy onset and release, and germination. Since only two genes encoding the GA deactivating GA 2-oxidase enzyme have been known so far in barley, this study also identified two new GA2ox genes designated as HvGA2ox1 and HvGA2ox3.

The Panama Canal Watershed (PCW) represents a special opportunity for studies related to seed dormancy in the tropics with both applied and basic research objectives. There is a clear need for seed information for nursery planning in restoration projects that involves use of a large number of local species. Moreover, the strong rainfall gradient along the 60 km of continuous lowland forest in the PCW represents an excellent opportunity to understand dormancy and its role as an adaptive trait that evolved in response to environmental factors. This study presents useful seed information for 100 tree species native to the PCW. For each species, it includes collection system, fruiting time, seed mass, seed moisture content, germination, and longevity in storage at 20??C. For the first time, an attempt is made to classify (to class sensu Baskin andamp; Baskin 2004) the class of dormancy in seeds of the PCW. An analysis of the relationship between class of dormancy and seed mass, moisture content, longevity, germination patterns, and seasonality is presented. The relationship between class of seed dormancy and longevity and geographical distribution of species within the watershed based on the rainfall gradient was investigated.

Inconsistent seed germination poses a problem for efficient seedling production of Echinacea species. Evidence suggests that ethylene can be effective for improving germination in Echinacea species. The objectives of this research were: to develop an ethylene pre-germination treatment that enhances germination in Echinacea species that is retained following drying and storage, and to determine if the ethylene effect on enhanced germination was an important mode of action for dormancy release. Four species of Echinacea (E. purpurea, E. tennesseensis, E. angustifolia and E. simulata) treated with 1-aminocyclopropane-1-carboxylic acid (ACC) or ethephon resulted in faster and generally higher germination. Pre-treatment of seeds with ACC or ethephon followed by drying was as effective as chilling stratification for enhancing germination depending on the species. While ethylene pretreatments did increase germination to some extent depending on species, it was concluded that 60-day stratification alone was a more commercially-viable treatment. Ethylene production or perception was not necessary for germination in untreated or stratified seeds as shown by aminoethoxyvinylglycine (AVG), silver thiosulfate (STS), and 1-methylcyclopropene (MCP) treatments. Both stratification and ACC treatment reduced Echinacea seed sensitivity to ABA and could be a common mechanism for enhanced germination. However, it does not appear that the increased germination seen after stratification was mediated through ethylene production because final germination percentages were generally unchanged following inhibition of ethylene production or action. In contrast, inhibition of ethylene production and perception reduced early 3-day germination suggesting that ethylene was more involved in seed vigor than final germination. It was determined that there is no physiological significance of ethylene for dormancy release in these Echinacea species.

Preharvest sprouting (PHS), the germination of seeds on the maternal plant before harvest, is a big challenge for barley producers worldwide. It is attributed mainly to low seed dormancy. The balance between two classical plant hormones, gibberellin (GA) and abscisic acid (ABA) regulates seed dormancy and germination, and the endogenous level of these two hormones in plants is determined by their biosynthesis and catabolism. This thesis characterized the expression patterns of the major GA and ABA metabolism genes in barley cv. Betzes during seed development, and germination in both dormant and non-dormant seeds. The results indicate that specific gene family members of the two hormones play distinct temporal roles in regulating seed development, dormancy onset and release, and germination. Since only two genes encoding the GA deactivating GA 2-oxidase enzyme have been known so far in barley, this study also identified two new GA2ox genes designated as HvGA2ox1 and HvGA2ox3.

Hazelnuts are mostly non-dormant at harvest but develop seed dormancy after a few days of storage. The seeds have been classified as recalcitrant since they cannot be stored for more than one year under ambient conditions. Cryopreservation has not been satisfactory so an alternative protocol is required. To test for recalcitrance, chilled non-dormant seeds (control) were compared with gibberellic acid (GA3) treated seeds during 6 weeks storage at 5°C or at ambient temperature. Control seed moisture content (MC) was 14-15% compared with 20% for GA3 treated seeds. No change in viability was noted until the end of 6 weeks at ambient temperature, when infection proliferated. Reduced germinability, associated with increased leachate conductivity, was noted on all treatments and controls, with ambient temperature storage most harmful for seed viability. This supports classification of hazel seeds as recalcitrant. However, orthodox behaviour could be induced by reducing seed moisture to <6%, showing survival for more than 3 years at -20°C with acceptable germinability and producing healthy seedlings. Pathogen tests show that 6 weeks chilling to break seed dormancy may activate the seeds’ internal protective mechanisms, thereby reducing infection and enabling germination and healthy seedling establishment. The link between seed viability and protection from free radicals and pathogens was examined. Antioxidant activity in hazelnut seed associates (such as endocarp, funiculus and testa) was found to be much higher than in the seed embryo, perhaps indicating that hazel seeds have natural protective mechanisms within the pericarp. Antioxidant activity of seed associates increased during chilling, indicating their role in protecting the seed. Nevertheless, TTC test revealed that seeds acclimatised to ii < 6% MC and stored at 5°C for 45 weeks showed viability loss due to damage of the embryonic axes, probably caused by free radicals. Initial tests to stabilise seed moisture content showed that reduction in seed moisture did not impose dormancy and seed moisture content (MC) stabilisation resulted in > 80% germination but many abnormal seedlings. Dormancy reversibility was tested by treatments T1 (one period at 15°C) and T2 (two periods at 15°C), designed following a consideration of the natural environment. Both resulted in reduced germination, delayed seedling emergence, increased abnormal seedlings, reduced seedling height and decreased internode numbers. To test the role of temperature in reduced seed performance, non-dormant hazelnuts were held at either 5°C or at ambient temperature for up to 6 weeks. Seeds from both sets exhibited high viability, but germinability was significantly decreased in the ambient temperature set, associated with increases in leachate conductivity and infection. Work in this thesis has confirmed that dormancy was broken by chilling, with gradually increasing germination as chilling time was increased. Germination increased with increase in chilling and reduction in infection. No infection was recoreded after 6 weeks chilling. It is most likely that protective agents are produced causing suppression of infection. In these experiments it was observed that not all germinated seeds produced healthy seedlings, suggesting that germination tests without observation of seedlings may give an incomplete assessment of germination success. Assessment using the Tetrazolium test (TTC) was found to be much more dependable and it was also possible to detect damage to specific tissues that might result in unhealthy seedlings.

Seed dormancy is a mechanism with great importance in plant fitness and it inhibits seed germination until is broken and seeds can germinate under optimal environmental conditions favorable for successful reproduction. Primary dormancy is contingent to the environment that seeds and the mother plant experience. Temperature is a major factor participating in the regulation of this complex trait. High and low levels of dormancy are induced during seed maturation by cold and warm temperatures respectively but the mechanism at the basis of temperature signaling in seeds is not well understood. Climate change and increased weather variability threaten the constant supply of high quality seeds into the market hence agriculture productivity. Therefore, understanding and taking control of the molecular mechanism behind the regulation of seed dormancy and germination will help to control and predict seed behavior in the field. Here I describe and discuss a forward genetic screen for the selection of mutant seed lines with altered seed dormancy in response to cool temperature during seed set. Putative mutant seed lines designated awake1 to awake52, were preliminarily characterized. Eleven awake lines were selected for further analysis and one was investigated in more detail. It was revealed that awake1 seeds shares common phenotype with seeds of a suberin deficient mutant which were previously reported to display increased dormancy but, here, I show they also display a reduction of seed dormancy. Segregation analysis suggests that the reduced dormancy phenotype is maternally inherited as the suberin deficient mutants. Also, transcriptomic analysis shows that many suberin associated genes are temperature-regulated. I conclude that control of suberin deposition may play a role in the regulation of dormancy in response to cool temperature.

A primary goal of ecological restoration is to establish desirable plant species. This goal is particularly important following the removal of invasive plants. Understanding biological traits of plant species important to revegetation is crucial to plant establishment. In the globally important Great Salt Lake (GSL) wetlands, native habitat-forming bulrushes Bolboschoenus maritimus, Schoenoplectus acutus, and S. americanus are frequently displaced by the invasive grass Phragmites australis. Successful revegetation of bulrushes relies on improving our understanding of seed dormancy break, seed germination requirements, and the environmental factors affecting rhizome emergence and growth. We used a series of germination chamber and greenhouse experiments to examine effective seed dormancy break treatments and germination conditions for multiple collection sites of bulrushes B. maritimus, S. acutus, and S. americanus. We also performed a greenhouse experiment to investigate how water depth, nutrient, and salinity levels affect B. maritimus and S. acutus emergence and growth from rhizomes. Cold, moist stratification and bleach scarification were effective dormancy break treatments for all species, though magnitude of effect varied by species and source site. Soaking the seeds after application of dormancy break treatments improved germination for all species. Rhizome emergence of S. acutus was negatively affected by high water depth, likely due to oxygen limitation. Bolboschoenus maritimus was salinity tolerant relative to S. acutus. GSL wetland managers can use these findings to improve revegetation projects via seeding and planting.

Globally, mining is vital to human interests, but its practice can cause landscape alteration which may look unnatural or engineered. The reintroduction of native plants to these areas is needed to restore the visual appeal and ecological function back into these altered mine lands. Cercocarpus ledifolius (curl-leaf mountain mahogany) is one desirable native species in the Intermountain West that is prized for its potential to grow on step and rocky hillsides and for the habitat it provides for wildlife. Unfortunately, C. ledifolius does not establish well from seed, which has been attributed to seed dormancy. The first objective of this study was to determine if scarification and gibberellic acid (GA3) treatments improve germination by alleviating seed dormancy. We also aimed to determine if a combination of fungicide and hydrophobic seed coatings increased emergence and establishment of C. ledifolius seedlings in mine overburden by reducing loss from fungal pathogens and premature germination. We found that two treatments, GA3 and GA3 + hydrophobic coatings, improved emergence compared to untreated seed, producing 1.8 (P = 0.0682), and 2.2 (P = 0.0751) more seedlings per meter, respectively. The second objective of this study was to make improvements in the laboratory to treatments explored in the field trial. We found that C. ledifolius seed responded inconsistently to treatments applied in the lab. The 15-minute acid scarified seed in combination with various GA3 seed coatings had significantly higher germination than untreated seed in one trial but had no difference in a second trial. Overall, these results indicate that seed enhancement technologies have the potential to improve C. ledifolius emergence in reclaimed mine lands, but additional research is needed to understand the species' dormancy characteristics better and improve the efficacy of the applied seed treatments.