Dormancy-breaking Requirements Research Articles

Effects of seed traits and dormancy break treatments on germination of four aquatic plant species

Germination biology and dormancy-breaking requirements of fully aquatic (submerged and floating) plant species remain relatively understudied. This is a significant impediment to efforts to restore vegetation in freshwater systems, where the abundance of seeds, and possibility of sowing them in large numbers, suggests underutilized potential for active revegetation. We assessed the influence of seed traits (mass and shape) and two treatments to break dormancy (scarification and gibberellic acid) on the germination of seeds of four macrophyte species after cold-stratification. For all species, untreated seeds did not germinate (0% rate), despite relatively high seed viability (42–90% across species). For Potamogeton illinoensis and P. natans, scarification plus gibberellic acid increased germination the most, to 83% and 35%, respectively (corrected for viability). The other two species remained wholly (Brasenia schreberi) or overwhelmingly (Nuphar variegata) ungerminated. For the two species that did germinate, germination probability increased with seed mass (P. natans and P. illinoensis) and elongation (P. natans). While the small size of trait effects relative to seed treatment effects suggests the latter are more important for revegetation work, the trait patterns highlight evolutionary tradeoffs in seed-size investments. The two Potamogeton species we examined show promise for use in revegetation via seeding, whereas B. schreberi and N. variegata dormancy break has not been adequately developed for these species to be used in seeding-based revegetation.

Reproductive strategies in the rare and endangered Killickia grandiflora (Lamiaceae) – implications for its urgent conservation

Populations of rare and restricted species are commonly challenged due to risks associated with reduced genetic diversity, environmental variation, and demographic stochasticity. Killickia grandiflora (Lamiaceae) is one of three Killickia species endemic to the Drakensberg Mountain Centre in KwaZulu-Natal, South Africa. Its confirmed distribution is restricted to a firebreak between two catchments in the Cathedral Peak region of the Ukhahlamba Drakensberg Transfrontier Park, where it is threatened by habitat transformation. In this study, we aimed to understand factors that promote or inhibit gene flow within this highly restricted K. grandiflora population, to estimate inbreeding, and to assess its status as a potentially threatened species. Exclusion and hand pollination trials indicate that K. grandiflora cannot autonomously self-pollinate and is dependent on pollinators for outcrossing. Germination trials and tetrazolium staining suggest that the seeds may have dormancy breaking requirements or are inviable. Inbreeding and genetic diversity analyses show that the K. grandiflora population nonetheless maintains a high level of genetic diversity, likely through outcrossing, despite the small population size and apparent poor reproductive success. We recommend that the IUCN conservation status of K. grandiflora be changed from Vulnerable to ‘Critically Endangered’ based on observed reductions in population size, limited extent of occurrence, small number of mature individuals, and threats by woody competitors. We strongly recommend that the known population(s) be monitored and the habitat patches be conserved regardless of size and maintained through regular burning to enable the species’ survival and conservation. Ex situ propagation and reintroduction to its historical habitat should be explored as additional conservation measures for this species.

Seed dormancy and germination in Cardiocrinum giganteum var. yunnanense, a perennial herb in China with post-dispersal embryo growth

Seeds of Cardiocrinum giganteum var. yunnanense, which is native to China, has underdeveloped embryos when dispersed from parent plants that did not grow until the second autumn and winter after exposure to summer temperatures. Radicles and cotyledons emerged in late winter and spring. Thus, a 15–16 month period was required from dispersal to seed germination. Under laboratory conditions, this period could be shortened to 5–6 months in a 25°C/15°C (60 days) → 15°C/5°C (60 days) → 5°C (60 days) temperature sequence. Based on dormancy-breaking requirements, the seeds have deep simple morphophysiological dormancy (MPD). This is practical knowledge for propagation of the species from seeds.

Seed Dormancy Breaking and Germination in Bituminaria basaltica and B. bituminosa (Fabaceae)

Most legumes are well-known for the physical dormancy of their seeds; hence, the implementation of appropriate scarification techniques is essential for introducing new legume crops within agricultural systems. This study investigated morpho-anatomical traits and dormancy-breaking requirements in two taxa of the genus Bituminaria: the widespread B. bituminosa and the point endemic B. basaltica. As the species under investigation show monospermic indehiscent legumes, pods were used in this research. We performed pod trait measurements, light microscopy observations on the seed coat anatomical structure, and germination tests after mechanical, thermal, and chemical scarification treatments for seed dormancy breaking. Moreover, germination performance at different pod maturity stages and storage times was tested. Differences in morpho-anatomical traits were found, with B. basaltica having a thicker palisade cell layer and B. bituminosa showing larger pods. All of the scarification treatments proved to be able to break physical dormancy, with mechanical and chemical scarification being the most effective methods in both species. Nevertheless, dormancy-breaking treatments performed better in B. bituminosa. Seeds at early pod maturity stages showed higher germination capacity in both species. Overall, this research provided background knowledge on seed collection time, storage strategy, and effective pre-sowing treatment, which might contribute to enhance propagation and use of Bituminaria species for multiple purposes. Under this perspective, the future characterization of additional Bituminaria genetic resources from other Mediterranean populations will have remarkable importance.

Assessment of the efficacy of some physico-chemical and hormonal treatments for dormancy removal & germination improvement in Bunium persicum (Kala Zeera)

The aim of this study was to determine the efficacy of some physico-chemical and hormonal treatments for dormancy removal / germination improvement. In laboratory experiment, seeds were subjected to various hormonal treatments like Gibberellic acid (0.01mM & 0.1mM), Indole Acetic acid (.01mM & 0.1mM) & Kinetin (0.01mM & 0.1 mM) for 24h. Seeds were also subjected to 24h, 48h running water for leaching and seed were kept for moist chilling at 4 0C for 2 months. Seeds were also treated with hormones (48h L +Kn (0.01 & 0.1mM); 48h L+GA3 (0.1mM) for 24h after 48h leaching. Seed germination was promoted by GA3 (0.1mM), IAA (0.01mM) and Kinetin (0.01mM). Kinetin (0.01 mM) was found to be most effective caused 77.33% germination within 150 days at 4 0C as compared to 60% in control. Leaching (24h & 48h) alone was not found to be effective, rather it was inhibitory for seed germination. Hormonal treatments (Kinetin 0.01 & 0.1 mM) when applied to seeds after 48h leaching enhanced seed germination. Lower concentration was found to be more effective, around 72% & 68% germination was observed at 48hL + Kn 0.01mM and 48h L + Kn 0.1mM, respectively as compared to 60% in control. Based on dormancy breaking requirements, it was confirmed that seeds failed to germinate under favourable conditions throughout the study period (8 months). However seeds germinate only at low temperature (4 0C). Pretreated seeds shifted from 4 0C to 25 0C got deteriorated within 10 days. The data indicate that seeds of Bunium persicum exhibit morpho physiological dormancy.

Seed germination of Paederotella pontica (Rupr. ex Boiss.) Kem-Nath.- rare endemic species of the Caucasus

Paederotella pontica is a Colchis tertiary relict species, regional narrow endemic to the Caucasus, representative of an oligotypic genus. The aim of this study was to determine dormancy-breaking requirements and develop seed germination protocol for P. pontica. Freshly matured seeds of P. pontica are morphophysiologically dormant (MPD). Mean length of seed is 820 μm, linear embryo is fully differentiated, on average 625 μm long. Penetration of tetrazolium salt indicates the permeability of seed coat and high percentage of vital seeds in capsules. Prior to root emergence, the E:S ratio increased from 0.76 to 0.9. Effects of warm and cold stratification and gibberellic acid (GA3) on embryo growth and seed germination were studied under laboratory conditions. Since cold stratification is the only requirement for the loss of MPD, the longest embryo growth occurred during this treatment and GA3 promoted MPD loss, we concluded that P. pontica seeds have intermediate complex MPD. Based on the treatment results a germination protocol is proposed: 1. Dry storage at 20°C, 2 months; 2. Cold-wet stratification at 3°C, 3 months; 3. Germination at 20/15°C day/night. Under developed conditions germination is fast, synchronous and yields to 80%.

The Influence of Dormancy Break Requirements on Germination and Viability Responses to Winter Submergence in Acorns of Three Bottomland Red Oak (Sect. Lobatae) Species

Abstract The objective of this study was to examine the relation of dormancy break requirements to winter submergence effects on germination and viability in cherrybark, willow, and Nuttall oak acorns. Acorns were submerged in a greentree reservoir and received 0, 21, 42, 63, or 84 days of winter submergence, followed by 8 weeks of incubation in four temperature regimes (15/6°, 20/10°, 25/15°, and 30/20° C). Winter submergence substituted for cold stratification requirements of cherrybark oak acorns, and dormancy break was achieved with 63 days of submergence. Although winter submergence exerted a positive effect on germination in Nuttall and willow oak acorns, dormancy break was not achieved in acorns of either species. Germination percentages were highest in the 30/20° C incubation temperature—cherrybark oak acorns (75–83 percent), followed by Nuttall oak (33–55 percent) and willow oak (14–52 percent). Among treatment combinations, all willow oak nongerminants were viable. Viability loss in cherrybark and Nuttall oak acorns was greatest in the 63- and 84-day treatments. The dynamics of acorn germination in response to winter hydrologic regime is influenced by submergence duration that may, or may not, satisfy dormancy break requirements in acorns of these red oak species.

Native leguminous plants for mineland revegetation in the eastern Amazon: seed characteristics and germination

For the effective use of native plants for mineland revegetation, an understanding of seed dormancy break and germination requirements, and seed storage tolerance is indispensable. In the present study, eight native species (Bauhinia pulchella, Bauhinia longipedicellata, Dioclea apurensis, Mimosa camporum, Mimosa acutistipula var. ferrea, Mimosa pudica, Parkia platycephala, and Stryphnodendron pulcherrimum) from the metalliferous savannas (cangas) and forests of Carajas Mineral Province, eastern Amazon-Brazil, were studied to determine seed size, seed quality (X-ray and tetrazolium tests), germination, and dormancy break requirements (boiling water, acid and mechanical scarification), and seed storage behavior. Our results showed considerable variation in seed size and percentage germination among the species. There was a strong relationship between seed size and germination, and the germination was greater for larger seeds from forests than smaller seeds from canga. All three scarification methods increased germination of M. camporum and M. acutistipula var. ferrea. Seeds of D. apurensis, M. acutistipula var. ferrea, M. pudica, and P. platycephala did not show a significant decline in germination after storage, indicating possible orthodox behavior. In contrast, B. pulchella, B. longipedicellata, M. camporum, and S. pulcherrimum showed behavior typical of recalcitrant or intermediate seeds since the germination of these species was reduced after storage. Further studies addressing seed dormancy break and seed storage in other native species are encouraged for a better use of native species in mineland revegetation.

The effects of temperature, water availability and seed burial depth on seed germination and seedling establishment of Calobota sericea (Fabaceae)

Calobota sericea is a perennial legume species from South Africa that has the potential to be implemented as a fodder crop in water-limited agro-ecosystems. Apart from dormancy breaking requirements, no information regarding the germination and seedling establishment requirements of C. sericea is currently available. Therefore, the aim of this study was to determine the germination and establishment abilities of C. sericea at different temperatures, water potentials and seed burial depths. In the first trial seeds were incubated at constant temperatures of 5–30 °C at 5 °C increments and in the second trial, seeds were incubated at 20 °C, at water potentials ranging from 0 to −1.0 MPa. The seedling emergence trial consisted of a complete randomised block greenhouse trial where seeds were sown at five burial depths (1–5 cm). Seeds were found to germinate best at temperatures ranging between 10 and 20 °C, but still had a germination percentage greater than 80% at 5 °C. The C. sericea seeds were also found to require a water potential of at least – 0.3 MPa to reach a germination potential of 60%, below which germination was severely impacted. Seedling emergence was found to be highest at burial depths of 2–4 cm. After establishment, seedlings generally displayed a decrease in above ground plant part height with increasing burial depth, but an increase in seedling mass. More resources, in terms of mass, were allocated to early root development as opposed to leaves and stems. Results from the current study therefore suggests that C. sericea seeds can be planted between 2 and 3 cm deep, during winter season, when temperatures are lower, and rainfall more prevalent and less erratic.

Seed dormancy and germination in Jeffersonia dubia (Berberidaceae) as affected by temperature and gibberellic acid.

The genus Jeffersonia, which contains only two species, has a trans-Atlantic disjunct distribution. The aims of this study were to determine the requirements for breaking dormancy and germination of J.dubia seeds and to compare its dormancy characteristics with those of the congener in eastern North America. Ripe seeds of J.dubia contain an underdeveloped embryo and were permeable to water. In nature, seeds were dispersed in May, while embryos began to grow in September, and were fully elongated by late November. Germination started in March of the next year, and seeds emerged as seedlings soon after germination. In laboratory experiments, incubation at high temperatures (25°C, 25/15°C) for at least 8weeks was required to initiate embryo growth, while a transfer to moderate temperatures (20/10°C, 15/6°C) was needed for the completion of embryo growth. At least 8weeks at 5°C was effective in overcoming physiological dormancy and for germination in seeds after the embryos had fully elongated. Thus, both high and low temperatures were essential to break dormancy. Gibberellic acid (GA3 ) treatment could substitute for the high temperature requirement, but not for the low temperature requirement. Based on the dormancy-breaking requirements, it is confirmed that the seeds have deep simple morphophysiological dormancy. This dormancy type is similar to that of seeds of the eastern North American species J.diphylla. Although seeds require 10-11months from seed dispersal to germination in nature, under controlled conditions they required only 3months after treatment with 1000mg·l(-1) GA3 , followed by incubation at 15/6°C. This represents practical knowledge for propagation of these plants from seed.

Dormancy-Breaking Requirements and Germination for Seeds of <i> Ostrya carpinifolia</i> Scop.

The present research aims at investigating the combined effects of warm stratification (WS)+cold stratification (CS), and gibberellic acid (GA 3 )+cold stratification (CS) on breaking dormancy and germination in seeds of Ostrya carpinifolia . The seeds were subjected to WS (20-25 ÂoC) for 0, 1 and 2 months and were subsequently cold stratified at 3-5 ÂoC for 0, 1, 2, 3 and 4 months (1st experiment). A further amount of seeds was treated with 500, 1000 or 2000 ppm GA 3 for 30 hours and then cold stratified at 3-5 ÂoC for 0, 1, 2, 3 and 4 months (2nd experiment). No germination was observed in the seeds subjected to only WS (1 and 2 months) or CS for 1 month indicating that the seeds of O. carpinifolia are dormant . A 4-month stratification (1 month WS+3 month CS or 4 month CS) fully released dormancy and led to a high germination percentage (94.17 and 98.34% respectively) in a short time (7.12 and 7.00 days respectively). Warm stratification treatment prior to CS, was not required in order to break the seed dormancy of O. carpinifolia and also did not reduce the length of the (total) stratification period required for breaking seed dormancy. Gibberellic acid (GA 3 ) application entirely replaced the CS period required for breaking seed dormancy. The germination of the seeds treated only with 2000 ppm GA 3 (0 months of CS) was (94.17%) as high as the germination of the seeds subjected to 4 months of CS (98.34%). It is obvious that the seedcoat of O. carpinifolia seeds was permeable to GA 3 and did not mechanically restrict embryo growth, thus, the seeds did not exhibit physical dormancy. Based on dormancy breaking requirements, the O. carpinifolia seeds displayed intermediate physiological dormancy.

Intermediate morphophysiological dormancy allows for life-cycle diversity in the annual weed, Turgenia latifolia (Apiaceae)

Our aim was to determine the seed dormancy-breaking requirements and type of life cycle of Turgenia latifolia in north-western China. At dispersal in July, only 0–9% of the seeds germinated at 5/2°C, 15/2°C, 20/10°C and 25/15°C; thus, 91% of the seeds exhibited physiological dormancy (PD) and 9% were non-dormant. Also, the embryo was underdeveloped and embryo length : seed length ratio increased from 0.38 in fresh seeds to 0.79 at germination. Seeds buried in dry soil at the four temperature regimes for 12 weeks germinated to ≥50% when tested in darkness at 5/2°C, and those buried at 15/2°C and 20/10°C germinated to ≥50% when tested at 15/2°C. Seeds have intermediate complex morphophysiological dormancy (MPD). PD was broken at high and/or low temperatures, but embryo growth was completed only at low temperatures; gibberellic acid (GA3) promoted germination. Seeds buried under natural conditions during summer germinated to ~70% and ~55% at 5/2°C and 15/2°C, respectively, in darkness in autumn. In a germination-phenology study, cumulative germination was ~20% and ~80% in autumn and spring, respectively. Intermediate complex MPD allows the species to behave as a winter annual and as a short-lived summer annual.

Ecological remarks on Astragalus maritimus and A. verrucosus, two threatened exclusive endemic species of Sardinia

Astragalus maritimus Moris and A. verrucosus Moris are two endemic threatened species exclusive of South West Sardinia. In this study the populations of both species were characterized and their seed germination investigated. The in situ results allowed reviewing their conservation status in compliance with the IUCN criteria, confirming the CR category by new subcriteria for both species. The germination study allowed identifying as well their dormancy breaking requirements.

Seed Dormancy-breaking and Germination Requirements of Two Atraphaxis Species

Atraphaxis spinosa and A.virgata are native shrubs in Urumqi.The two species are important for the desert ecosystem.Seeds of the species were dormant at maturity.Dormancy break occurred during cold stratification at 5℃ for 8 weeks and 6 weeks,also at the habitat in winter.Seeds stratified at 5℃ and habitat and incubated at 12/12 h daily temperature regimes of 15/6,20/10,25/15 and 30/20℃ geminated faster and to a significantly higher percentage at each temperature regime than those not stratified.Seeds of A.spinosa were more deeper dormant than A.virgata.Their seeds were shallow non-deep physiological dormancy.

Morphological and physiological dormancy in seeds of Aegopodium podagraria (Apiaceae) broken successively during cold stratification

AbstractA low-temperature requirement for dormancy break has been observed frequently in temperate-climate Apiaceae species, resulting in spring emergence of seedlings. A series of experiments was performed to identify dormancy-breaking requirements of Aegopodium podagraria, a nitrophilous perennial growing mainly in mildly shaded places. In natural conditions, the embryos in seeds of A. podagraria grow in early winter. Seedlings were first observed in early spring and seedling emergence peaked in March and April. Experiments using temperature-controlled incubators revealed that embryos in seeds of A. podagraria grow only at low temperatures (5°C), irrespective of a pretreatment at higher temperatures. Seeds did not germinate immediately after embryo growth was completed, instead an additional cold stratification period was required to break dormancy completely. Once dormancy was broken, seeds germinated at a range of temperatures. Addition of gibberellic acid (GA3) had a positive effect on embryo growth in seeds incubated at 10°C and at 23°C, but it did not promote germination. Since seeds of A. podagraria have a low-temperature requirement for embryo growth and require an additional chilling period after completion of embryo growth, they exhibit characteristics of deep complex morphophysiological dormancy.

Environmental regulation of dormancy loss in seeds of Lomatium dissectum (Apiaceae)

Lomatium dissectum (Apiaceae) is a perennial, herbaceous plant of wide distribution in Western North America. At the time of dispersal, L. dissectum seeds are dormant and have under-developed embryos. The aims of this work were to determine the requirements for dormancy break and germination, to characterize the type of seed dormancy, and to determine the effect of dehydration after embryo growth on seed viability and secondary dormancy. The temperature requirements for embryo growth and germination were investigated under growth chamber and field conditions. The effect of GA(3) on embryo growth was also analysed to determine the specific type of seed dormancy. The effect of dehydration on seed viability and induction of secondary dormancy were tested in seeds where embryos had elongated about 4-fold their initial length. Most experiments examining the nature of seed dormancy were conducted with seeds collected at one site in two different years. To characterize the degree of variation in dormancy-breaking requirements among seed populations, the stratification requirements of seeds collected at eight different sites were compared. Embryo growth prior to and during germination occurred at temperatures between 3 and 6 degrees C and was negligible at stratification temperatures of 0.5 and 9.1 degrees C. Seeds buried in the field and exposed to natural winter conditions showed similar trends. Interruption of the cold stratification period by 8 weeks of dehydration decreased seed viability by about 30 % and induced secondary dormancy in the remaining viable seeds. Comparison of the cold stratification requirements of different seed populations indicates that seeds collected from moist habitats have longer cold stratification requirements that those from semiarid environments. Seeds of L. dissectum have deep complex morphophysiological dormancy. The requirements for dormancy break and germination reflect an adaptation to trigger germination in late winter.

The role of temperature in post-dispersal embryo growth and dormancy break in seeds of Aconitum lycoctonum L.

This research was performed to resolve temperature requirement for embryo growth, dormancy break and seed germination of Aconitum lycoctonum, an Eurasian perennial herb growing in deciduous forests. The dormancy strategy of A. lycoctonum was compared with that of other Ranunculaceae species growing in the temperate deciduous forest habitat. Seeds of A. lycoctonum germinate immediately after embryo growth is completed during winter and seedlings subsequently emerge in early spring. Experiments in controlled conditions revealed that (1) embryo growth and germination only occurred at low temperatures (<10 °C), (2) a high-temperature pre-treatment was not required for germination, and (3) application of gibberellic acid did not overcome the chilling requirement. Based on these results, seeds of A. lycoctonum can be classified as having deep complex morphophysiological dormancy. Dormancy breaking requirements of A. lycoctonum are very similar to related species studied before, suggesting stasis in seed dormancy traits has occurred in the Aconitum–Delphinium clade.

Interspecific variations in seed germination of Corylopsis

This study was initiated to investigate the differences in germination percentages and rates between Corylopsis coreana Uyeki and Corylopsis sinensis var. calvescens Rehder & E.H. Wilson following a warm stratification (WS) and cold stratification (CS), and to study the effect of different WS temperatures interacting with different durations of CS. Warm stratification at 10 °C, 15 °C, 20 °C, and 25 °C was given for 1 month (1 M 10 °C, 15 °C, 20 °C, and 25 °C WS) followed by 0 M, 1 M, 2 M, and 3 M of CS at 5 °C (0 M, 1 M, 2 M, 3 M CS) and seeds were germinated in an air conditioned greenhouse maintained at 18.5 °C/18 °C. On average, less than 1% of C. coreana seeds germinated when sown without any WS and CS or with 1 M 15 °C, 20 °C, and 25 °C WS without CS treatment. However, 26% C. coreana seeds germinated after 1 M 10 °C WS without any CS treatment. Germination was not affected by WS temperatures when followed by 2 M 5 °C CS. It is concluded that C. coreana exhibited low seed germination at 10 °C and that this temperature could be considered the upper limit of CS for C. coreana. Only 2 M CS was required for more than 90% seeds to germinate. However, C. sinensis var. calvescens required longer than 3 M CS for more than 29% seeds to germinate. This clearly shows that there is an interspecific variation in optimum dormancy-breaking requirements.

Multiple environmental signals required for embryo growth and germination of seeds of Selinum carvifolia (L.) L. and Angelica sylvestris L. (Apiaceae)

AbstractGermination and dormancy breaking requirements were studied in Selinum carvifolia (L.) L. and Angelica sylvestris L. (Apiaceae). Seeds of these two species have an underdeveloped embryo and are morpho-physiologically dormant. The embryo does not start to grow until physiological dormancy is broken by cold stratification. Incubating seeds at fluctuating temperatures in the light, after cold stratification, had a stimulating effect on embryo growth and seed germination. Seeds of S. carvifolia and A. sylvestris have non-deep simple morphophysiological dormancy (MPD), since gibberellic acid (GA3) could substitute for cold stratification. This is the first report of non-deep simple MPD that is broken by cold stratification in the Apiaceae. Under natural conditions, physiological dormancy is broken by low temperature conditions during winter. Embryo growth and germination occur in a short time interval when temperatures start rising in early spring. Due to the fact that multiple environmental signals regulate dormancy, seedling emergence in these species is timed very accurately in spring.

The interaction of light and low temperature on breaking the dormancy of Chara vulgaris oospores

Germination and dormancy-breaking requirements have been investigated of Chara vulgaris, L. oospores harvested from surface sediments and from the plants of two lakes, Schumacher and Little Pearl in the locality of Timmins, northern Ontario. Oospores exhibited contrasting germination rates of 4–5% for fresh and 28–45% for sedimentary oospores. Dormancy of sedimentary oospores was readily broken by after-ripening for 60 days at 4 °C followed by exposure to white or red light, or by gibberellic acid (GA) in light (49–74% germination), whereas fresh oospores were less responsive (12–22% germination) to such treatments. Treatment of oospores by stratification or with GA or exposure to red light caused the induction of α-amylase activity. Abscisic acid reduced the effect of stratification and inhibited the GA-enhanced germination of sedimentary oospores, providing evidence of the participation of a phytochrome mechanism and hormonal regulation in the breaking of oospore dormancy. These results indicate that C. vulgaris oospores exhibit primary dormancy when first released from the parent plant, which is broken by exposure to low temperature, followed by secondary dormancy which is broken by a further period of stratification and exposure to light. Oospores from both lakes responded similarly to the dormancy-breaking treatments, but their overall viabilities were significantly different.