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Servet Caliskan, Sharon T. Kester, and Robert L. Geneve

Primary physiological dormancy is a basic concept for courses that emphasize general plant propagation or specific courses in seed biology or technology. Primary seed dormancy is a condition where seeds will not germinate even when the environmental

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Hailin Liu, Cunmeng Qian, Jian Zhou, Xiaoyan Zhang, Qiuyue Ma, and Shuxian Li

moist prechill treatment at 3–5 °C for 3–4 months. In this study, we aimed to identify the multifaceted causes and to establish a practical and powerful method to successfully break the seed dormancy of C. florida that can be applied in seed

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Scott B. Lukas, Joseph DeFrank, and Orville C. Baldos

Plants produce seeds to ensure the greatest establishment and survival success for future generations ( Stoehr and El-Kassaby, 2011 ). One innate mechanism to increase seedling success is seed dormancy. The critical function of dormancy is to

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Robert L. Geneve

Seed dormancy in Eastern redbud (Cercis canadensis var. canadensis L.) can be overcome by seedcoat scarification to allow water imbibition, followed by chilling stratification to permit germination. During chilling stratification, there was an increase in the growth potential of the embryo as indicated by the ability of the isolated embryo to germinate in osmotic solutions. Penetration resistance of the testa also decreased after chilling stratification. The combination of seedcoat alteration and the increase in embryonic growth potential was associated with overcoming dormancy in redbud seed. GA3 or ethephon (50 μm) stimulated germination (28% and 60%, respectively) and increased the growth potential of treated embryos. Chemical names used: gibberellic acid (GA3), (2-chloroethyl) phosphoric acid (ethephon).

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Noël Pallais, José Santos-Rojas, and Rosario Falcón

Sexual potato (Solanum tuberosum L.) seeds require many months of afterripening in dry storage to completely lose dormancy and germinate readily at >25C. We examined the relationship between storage temperature and seed dormancy, as assessed by the percentage of germination after 4 days. Two F1 hybrid lots of `Desiree' × 7XY.1 were used; one seed lot was produced by carefully removing half of the developing tubers from the mother plant during seed development, and the control remained undisturbed. Seeds were stored with 3.4% moisture (dry-weight basis) at 10, 20, 30, 40, and 50C and were tested eight times during 29 months for daily germination at 27/40C (21/3 h) for the first 8 days, followed by 6 days at 17C. After 29 months of storage, final germination was <97% only when control seeds were stored at 50C, in which germination was 72%. Germination after 4 days increased curvilinearly with increasing storage temperature, and both seed lots similarly lost dormancy (germination >90%) after 10 months at 40C. Optimum germination levels were maintained after 29 months at 40C. Seeds stored at 50C never completely lost dormancy, and after 7 months of storage, germination at 4 days gradually decreased to zero. Dormancy was eventually lost after 29 months in most seeds stored at <40C, and differences between seed lots suggest that removing tubers from the mother plant increased dormancy. We conclude that dry potato seeds can be safely afterripened at temperatures up to 40C; lower temperatures slow the rate of dormancy loss, and higher ones are detrimental to seed quality.

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E. Carvajel-Millan, A.A. Gardea, V. Guerrero-P, F. Goycoolea, and C. Rivera

Apple embryos from moist seeds kept at 4 °C were used for a calorimetric characterization of Red and Golden Delicious apple seed dormancy. Seeds were sampled at 100-h intervals during 1200 h. The metabolic response of such samples was compared to that from chilled Golden Delicious seeds (>1200 h) stored under controlled atmosphere (CA). Isothermal calorimetry at 25 °C, evaluated metabolic activity (q), respiration rate (RCO2), metabolic 65 °C estimated activation energy (Ea) in a 10 to 20 °C range, and respiration coefficients (Q10) from 10 to 50 °C at 10 °C intervals. Data showed a direct relationship between chilling exposure and embryo metabolic responses from both cultivars. Once chilling requirement was satisfied, Red and Golden Delicious seeds presented a significant increase (P ≤ 0.05) in q, 0.94 and 0.98 μW/mg dry weight (dw); RCO2, 9.9 and 7.6 mmol CO2/mg dw; and RSG·ΔHB, 3.6 and 2.5 μW/mg dw, respectively. On the other hand, q/RCO2 did not follow a definite pattern, neither in Red nor Golden Delicious cultivars. Ea decreased 19.2 and 23.4 J/mol per °K per mg dw in Red and Golden Delicious, respectively, as a function of seed chilling. Q10 showed a significant response to temperature, but not to chilling exposure. Golden Delcious seeds from CA showed a significant reduction on q, RCO2, and RSG·ΔHB of 0.28 μW/mg dw, 2.47 mmol CO2/mg dw, and 14 μW/mg dw, respectively. Results show that calorimetry is a sufficiently sensitive, fast, and precise tool to quantify metabolic responses during seed chilling, as evolving energy.

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Dianne Oakley, Julie Laufmann, James Klett, and Harrison Hughes

Propagation of Winecups [Callirhoe involucrata (Torrey & A. Gray)] for use as a landscape ornamental has been impeded by a lack of understanding of the seed dormancy and a practical method for overcoming it. As with many members of the Malvaceae family, C. involucrata produces hard seed. In the populations tested, it accounted for 90% of an average sample. Impermeability, however, is not the only limiting factor to germination. Three disparate populations of seed, representing two different collection years have been investigated using moist pre-chilling, boiling water, leaching, gibberellic acid, hydrogen peroxide and mechanical and chemical scarification methods. Scarifying in concentrated sulfuric acid stimulates germination of some seed fractions and causes embryonic damage in others, suggesting variation in seed coat thickness. Similar results were obtained using a pressurized air-scarifier; the hard seed coat of some seed fractions were precisely scarified while others were physically damaged using the same psi/time treatment. Placing seed in boiling water increases germination from 4%, 7%, and 18 % to 23%, 25%, and 77% in the three populations, respectively. Leaching for 24/48 h in cold (18 °C) aerated water or for 24 h in warm (40 °C) aerated water showed only a minor increase over the control. Pre-chilling at 5 °C for 30, 60, and 90 days showed no improvement over the control. Gibberellic acid-soaked blotters improved germination at 400 ppm to 20%, 10%, and 41%; at 500 ppm germination was reduced. Soaking seed for 24 h in a 3% concentration of hydrogen peroxide did not effect germination; at a 30% concentration germination was reduced. The considerable variation in seed dormancy expression may be a function of differences in environmental factors during development or seed age.

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Barry Duncil and Robert Geneve

Wild rye (Elymus) contains several species of cool season grasses that are important components of forest and woodland ecosystems. Little specific information is known about seed dormancy in wild rye species, but cool season grasses generally display endogenous, non-deep physiological dormancy that would normally be satisfied by moist chilling during winter to permit early spring germination. However, few studies have documented the effect of extended chilling stratification on dormancy release in cool season grasses. Therefore, the objective of this study was to document the dormancy condition of representative wild rye species and to observe the impact of chilling stratification on dormancy release. Three species of wild rye (E. virginicus, E. macgregorii, and E. villosus) were selected based on their taxonomic and ecological relationships. All species showed conditional dormancy with respect to germination temperature. At 15 °C, E. virginicus, E. macgregorii, and E. villosus germinated at 75%, 81%, and 40%, respectively, compared to 5%, 3%, and 12% for each species at 20 and 25 °C. Chilling stratification at 10 °C improved germination compared to non-stratified seeds to 95% and 94% for E. m acgregorii and E. villosus, but had no effect or reduced germination in E. virginicus. Stratification at 5 °C was not as effective as 10 °C for dormancy release and appeared to cause chilling injury in E. virginicus and E. macgregorii. The data suggest that these wild rye species express a form of conditional endogenous, non-deep physiological dormancy that is most pronounced when seeds are germinated at non-optimal temperatures.

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Luping Qu, Xiping Wang, Ying Chen, Richard Scalzo, Mark P. Widrlechner, Jeanine M. Davis, and James F. Hancock

Seed germination patterns were studied in Echinacea purpurea (L.) Moench grouped by seed source, one group of seven lots from commercially cultivated populations and a second group of nine lots regenerated from ex situ conserved wild populations. Germination tests were conducted in a growth chamber in light (40 μmol·m–2·s–1) or darkness at 25 °C for 20 days after soaking the seeds in water for 10 minutes. Except for two seed lots from wild populations, better germination was observed for commercially cultivated populations in light (90% mean among seed lots, ranging from 82% to 95%) and in darkness (88% mean among seed lots, ranging from 82% to 97%) than for wild populations in light (56% mean among seed lots, ranging from 9% to 92%) or in darkness (37% mean among seed lots, ranging from 4% to 78%). No germination difference was measured between treatments in light and darkness in the commercially cultivated populations, but significant differences were noted for treatments among wild populations. These results suggest that repeated cycles of sowing seeds during cultivation without treatments for dormancy release resulted in reduced seed dormancy in E. purpurea.

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Michael Stein, Corina Serban, and Per McCord

Seed dormancy, specifically endodormancy, is a strong inhibitor of rapid germination in stone fruit seeds, including those of sweet cherry ( Prunus avium ). Endodormancy has been suggested to be a crucial process in seeds because it prevents