Some effects of temperature during seed development on carrot (Daucus carota) seed growth and quality

The growth and development of carrot seeds cv. Chantenay Red-cored Royal Chantenay at day/night temperatures of 20/10°C, 25/15°C and 30/20°C and subsequent seed performance were examined in 1984 and 1985. An increase in temperature from 20/10°C to 30/20°C reduced mean weight per seed by 20% in 1984 and by 13% in 1985. There were no effects of temperature on endosperm + embryo weight, or on endosperm cell number but the weight of pericarp decreased with an increase in temperature. Seeds grown at the highest temperature had the largest embryos and the highest nitrogen, DNA and rRNA content; they germinated and emerged earlier, and gave higher percentage seedling emergence than those grown at the lowest temperature. There were no effects of temperature during seed growth on the rate of imbibition of water by seeds during the germination process.     

Morphophysiological dormancy in seeds of the ANA grade angiosperm Schisandra arisanensis (Schisandraceae)

We determined the kind of seed dormancy in Schisandra arisanensis, an ANA grade ([A]mborellales [N]ymphaeales [A]ustrobaileyales) angiosperm with medicinal value. Seeds have small underdeveloped embryos, and following seed maturity their length increased approximately 360% before radicle emergence. Germination was delayed 6–8 weeks, and the percentage and rate were much higher at 15/6, 20/10 and 25/15°C than at 30/20°C. For seeds incubated at 5/5°C (8 weeks) → 15/6°C (4 weeks) → 20/10°C (8 weeks) → 25/15°C (12 weeks) → 20/10°C (5 weeks), embryos grew at 15/6°C → 20/10°C, and almost all seeds that germinated (89%) did so at 20/10°C → 25/15°C. When seeds were incubated in a complementary temperature sequence, 25/15°C (12 weeks) → 20/10°C (8 weeks) → 15/6°C (4 weeks) → 5/5°C (9 weeks) → 15/6°C (4 weeks), embryos grew at 25/15°C → 20/10°C. Nearly all seeds that germinated (93%) did so at 25/15°C → 20/10°C and at 15/6°C following 9 weeks at 5/5°C. Based on the temperature requirements for embryo growth and seed germination, seeds of this species have non‐deep simple morphophysiological dormancy (C_1bB).     

The Effects of Temperature upon Seed Development in Three Species of Forage Grasses

The effects of three temperature regimes, 25°C day/20°Cnight, 20°C day/15°C night and 15°C day/10°Cnight upon seed development in S.22 Italian ryegrass, S.24 perennialryegrass, S.215 meadow fescue and a Swiss ecotype of meadowfescue were investigated. The largest ovaries and largest seedswere obtained from the 15/10°C environment and floret fertilitywas greatest at 20/15°C. The largest seed weight per inflorescencewas at 20/15°C, except for the Swiss ecotype of meadow fescuewhere it was greatest at 15/10°C. The percentage germinationwas highest from those seeds developed at 25/20°C and thiswas particularly marked at germination temperatures of 13–20°C.There was a low rate of germination of seeds from the 15/10°Ctreatment, but they produced seedlings with the largest dryweights. It is concluded that year to year temperature differenceswill affect the yield and quality of seed crops of forage grasses.     

Effects of seed colour heterogeneity on germination behaviour of the desert plant Lotononis platycarpa (Fabaceae)

We aimed to determine the ecological role of three seed morphs observed for the first time in a desert population of Lotononis platycarpa (Fabaceae), with respect to their germination requirements. Seeds sorted by seed coat colour (olive green, orange and brown) were germinated under laboratory conditions under two photoperiods (12/12‐h light and continuous dark) and three alternating temperature regimes (15/25, 20/30, 25/35°C). We found that the three distinct seed types differ in their seed mass, germination percentage and speed of germination. Overall, the light‐incubated seeds germinated with higher percentages than seeds in the total darkness. Furthermore, seeds with orange coat germinated with higher percentages at 15/25 and 25/35°C (up to 60%, for both) and significantly faster than the other two colour morphs. Our results suggest an adaptive significance of seed colour heterogeneity in the harsh desert habitat inhabited by the study species.     

The germination characteristics of <Emphasis Type="Italic">Scrophularia marilandica</Emphasis> L. (Scrophulariaceae) seeds

Investigations on seeds of Scrophularia marilandica L. were undertaken to determine their germination requirements. Seeds were collected from three naturally occurring sites and one greenhouse-grown population in London, Ontario in September and October of 1997. Some were set to germinate immediately after collection; others were stored in or on soil outside and/or under controlled laboratory conditions before testing. Germination was assessed under two light/temperature regimes (35°C 14 h light, 20°C 10 h dark and 25°C 14 h light, 10°C 10 h dark), in continuous darkness, and in the presence of two germination-promoting chemicals (GA₃ and KNO₃). Fresh seeds germinated best at 35/20°C, while stored seeds germinated best at 25/10°C. No differences in percent germination were found among three seed-maturity stages. All chemical treatments, except 0.01 M KNO_3, increased percent germination. Significant differences were found both among and within sites for most chemical treatments, but exposure to 3 × 10⁻⁴ M GA₃ caused almost every seed to germinate. When compared to the control, both the gibberellic acid and the soil-storage treatments contributed to faster germination. Exposure of seeds to naturally prevailing conditions on the soil surface followed by testing under the 25/10°C regime produced the highest percent germination. No seeds germinated in the dark. In summary, seeds of S. marilandica exhibit physiological dormancy, which can be alleviated by exposure to light, after-ripening and/or cold stratification. It is probable that the differences in germination response among sites can be attributed to differences in environmental conditions during seed production. These experiments indicate that the seeds of S. marilandica must be buried shortly after dispersal in order to form a persistent seed bank.     

Seed dormancy-breaking and germination requirements ofDrosera anglica,an insectivorous species of the Northern Hemisphere

Seeds of Drosera anglica collected in Sweden were dormant at maturity in late summer, and dormancy break occurred during cold stratification. Stratified seeds required light for germination, but light had to be given after temperatures were high enough to be favorable for germination. Seeds stratified in darkness at 5/1 °C and incubated in light at 12/12 h daily temperature regimes of 15/6, 20/10 and 25/15 °C germinated slower and to a significantly lower percentage at each temperature regime than those stratified in light and incubated in light. Length of the stratification period required before seeds would germinate to high percentages depended on (1) whether seeds were in light or in darkness during stratification and during the subsequent incubation period, and (2) the temperature regime during incubation. Seeds collected in 1999 germinated to 4, 24 and 92 % in light at 15/6, 20/10 and 25/15 °C, respectively, after 2 weeks of stratification in light. Seeds stratified in light for 18 weeks and incubated in light at 15/6, 20/10 and 25/15 °C germinated to 87, 95 and 100 %, respectively, while those stratified in darkness for 18 weeks and incubated in light germinated to 6, 82 and 91 %, respectively. Seeds collected from the same site in 1998 and 1999, stratified in light at 5/1 °C and incubated in light at 15/6 °C germinated to 22 and 87 %, respectively, indicating year-to-year variation in degree of dormancy. As dormancy break occurred, the minimum temperature for germination decreased. Thus, seed dormancy is broken in nature by cold stratification during winter, and by spring, seeds are capable of germinating at low habitat temperatures, if they are exposed to light.     

Effects of drought stress on seed germination of ornamental sunflowers

The response to drought stress on germination was investigated on three hybrids of ornamental sunflower, ‘Hadar’, ‘Pazit’, and ‘Zohar’. Different levels of water potential [Ψ: 0.0 (control), ?0.15, ?0.30, ?0.45, ?0.60, ?0.75, and ?0.90 MPa] were adopted using polyethylene glycol-6000 (PEG6000) at four germination temperatures (15, 20, 25, and 30 °C). Final germination percentage, mean germination time, germination index, germination rate index, and germination stress tolerance index were used to evaluate the genotype response to PEG-induced water stress. Shoot and root length and fresh and dry weight were measured on seeds germinated at 20 °C under the different levels of water potentials. During germination, the three ornamental sunflowers showed to be more sensitive to suboptimal temperature than to supraoptimal. Decreasing water potential of imbibition solution progressively inhibited and delayed seed germination. Among cultivars, ‘Hadar’ and ‘Pazit’ performed better at temperature lower than 30 °C. ‘Zohar’ showed a lower sensitivity to PEG-induced water stress at all temperature conditions. Water stress during seed germination depressed the following seedling growth under favourable conditions. As a result, shoot and root length and fresh and dry weight was significantly lower in seedlings from seed germinated at ψ ≤ 0.45 MPa.     

九里香种子脱水耐性和萌发生理的研究

九里香种子自花后 42～ 77d,含水量和电导率逐渐降低 ,种子干重、发芽率、发芽指数和活力指数逐渐增加。硅胶脱水 1～ 6d后 ,种子含水量下降 1 0 %～ 3 5 % ,发芽率、发芽指数和活力指数均有不同程度的降低 ,不同发育时期九里香种子的脱水耐性有别 ,花后 42～ 70d不断增强 ,77d有所减弱。花后 70d的种子含水量降至 1 0 % ,种子发芽率无明显降低 ;含水量为 9%的种子在 4°C和 2 0°C的低温条件贮存 3 0d和 42d ,多数种子仍能萌发 ,这表明九里香种子是一种正常型种子。光照能促进种子的萌发 ;在 2 0～ 3 0°C、室温和 2 0 /3 0°C变温条件下种子萌发较好 ;光照和温度对种子萌发有单独影响 ,但又相互作用 ,同时光照对萌发的影响还与种子含水量有关。     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.): VII. INFLUENCE OF AFTER-RIPENING AND AGEING ON GERMINATION RESPONSES TO TEMPERATURE AND WATER POTENTIAL

The effects of storage conditions on the germination of developingmuskmelon (Cucumis melo L.) seeds were tested to determine whetherafter-ripening is required to obtain maximum seed vigour. Seedswere harvested at 5 d intervals from 35 (immature) to 60 (fullymature) days after anthesis (DAA), washed, dried, and storedat water contents of 3·3 to 19% (dry weight basis) at6, 20, or 30°C for up to one year. Germination was testedin water and in polyethylene glycol 8000 solutions ( –0·2to –1·2 MPa osmotic potential) at 15, 20, 25 or30°C. Germination percentages and rates (inverse of meantimes to radicle emergence) were compared to those of newlyharvested, washed and dried seeds. For 40 and 60 DAA seeds,one year of storage at 20°C and water contents <6·5%significantly increased germination percentages and rates at20°C, but had little effect on germination at 25 and 30°C.Storage reduced the estimated base temperature (T_b) and meanbase water potential (_b) for germination of both 40 and 60 DAAseeds by approximately 5°C and 0·3 MPa, respectively.Immature 35 DAA seeds showed the greatest benefit from storageat 3 to 5% water content and 30°C, as germination percentagesand rates increased at all water potentials (). Storage underthese same conditions had little effect on the germination ofmature seeds in water, but increased germination percentagesand rates at reduced 's. Accelerated ageing for one month at30°C and water contents from 15 to 19° increased germinationrates and percentages of mature seeds at reduced 's, but longerdurations resulted in sharp declines in both parameters. Immatureseeds lost viability within one month under accelerated ageingconditions. An after-ripening period is required at all stagesof muskmelon seed development to expand the temperature andwater potential ranges allowing germination and to achieve maximumgerminability and vigour. Post-harvest dormancy is deepest atthe point of maximum seed dry weight accumulation and declinesthereafter, both in situ within the ripening fruit and duringdry storage. Key words: Muskmelon, Cucumis melo L., seed, development, dormancy, germination, vigour, after-ripening     

Viability of onion (Allium cega) seed as influenced by temperature during seed growth

The yield and performance of seeds from crops of winter-hardy, bolting-resistant onion grown at temperatures of 15–16, 18–19 and 22–23°C in 1979, 1980 and 1982 were compared. Yields of seed from crops grown at 22–23°C were lower than those from crops grown at lower temperatures but the seeds ripened between 11 and 32 days earlier. Seeds from crops grown at mean temperatures of above 18°C gave higher percentage germination when imbibed at 30°C than 20°C and they also gave higher percentage seedling emergence than those from crops grown at lower temperatures. Seedlings from seeds produced at mean temperatures above 18°C were heavier than those from seeds of a similar weight but produced at lower temperatures. None of these differences were associated with differences in seed weight, embryo weight or seed dormancy but were positively correlated with differences in seed N-concentration. The differences were also associated with the rate of imbibition of water as high germination, high N-content seeds had a slower rate of imbibition than low germination, low N-content seeds of the same weight.     

Effects of maternal salinity on salt tolerance during germination of Suaeda aegyptiaca,a facultative halophyte in the Arab Gulf desert

Suaeda aegyptiaca is a facultative halophyte found in saline and non‐saline habitats of the Arab Gulf desert, which produces small‐sized undispersible seeds. The interactive effects of maternal salinity and other environmental conditions, such as salinity, light and temperatures, that are prevailing during seed germination have received little attention for a facultative halophyte. This study tested the effects of maternal salinity on salt tolerance during seed germination of S. aegyptiaca under different light and temperature regimes. Seeds collected from both saline and non‐saline habitats of the United Arab Emirates (UAE) were germinated in 0, 50, 100, 200 and 400 mM NaCl, and incubated at 15/25°C, 20/30°C and 25/35°C in both 12‐h light/12‐h dark regimes and continuous darkness. Generally, seeds of the non‐saline habitat were 56% heavier and attained greater germination at the lower temperatures than seeds of the saline habitat. Seeds of the saline habitat germinated better in saline solutions at higher temperatures and in light. Germination was faster for seeds of the saline habitat than for seeds of non‐saline habitats. Germination recovery after transfer to distilled water was significantly greater for seeds from the non‐saline habitat, compared with seeds from saline habitats. Recovery was greater at lower and/or moderate temperatures, compared with at higher temperatures. Germination was significantly faster during recovery, compared with in the saline solutions. The study indicates that the maternal effect of salinity was confounded with the seed‐size effect and it cannot be conclusively confirmed.     

Combinational dormancy in seeds of Sicyos angulatus (Cucurbitaceae,tribe Sicyeae)

Seeds with a water‐impermeable seed coat and a physiologically dormant embryo are classified as having combinational dormancy. Seeds of Sicyos angulatus (burcucumber) have been clearly shown to have a water‐impermeable seed coat (physical dormancy [PY]). The primary aim of the present study was to confirm (or not) that physiological dormancy (PD) is also present in seeds of S. angulatus. The highest germination of scarified fresh (38%) and 3‐month dry‐stored (36%) seeds occurred at 35/20°C. The rate (speed) of germination was faster in scarified dry‐stored seeds than in scarified fresh seeds. Removal of the seed coat, but leaving the membrane surrounding the embryo intact, increased germination of both fresh and dry‐stored seeds to > 85% at 35/20°C. Germination (80–100%) of excised embryos (both seed coat and membrane removed) occurred at 15/6, 25/15 and 35/20°C and reached 95–100% after 4 days of incubation at 25/15 and 35/20°C. Dry storage (after‐ripening) caused an increase in the germination percentage of scarified and of decoated seeds at 25/15°C and in both germination percentage and rate of excised embryos at 15/6°C. Eight weeks of cold stratification resulted in a significant increase in the germination of scarified seeds at 25/15 and 35/20°C and of decoated seeds at 15/6 and 25/15°C. Based on the results of our study and on information reported in the literature, we conclude that seeds of S. angulatus not only have PY, but also non‐deep PD, that is, combinational dormancy (PY + PD).     

Germination Response Patterns during Dormancy Loss in Achenes of Six Perennial Asteraceae from Texas, USA

Abstract When subjected to simulated habitat temperatures, achenes of six perennial Asteraceae from southcentral Texas came out of dormancy during summer. In the early stages of dormancy loss, achenes of Erigeron modestus, Gaillardia suavis and Hymenoxys scaposa germinated (to ≥ 10%) in light at 12/12 hr daily thermoperiods of 15/6, 20/10 and 25/15°C and those of Pinaropappus roseus at 15/6 and 20/10°C. After additional dormancy loss, achenes of these four species also germinated at 30/15 and 35/20°C. Achenes of these four species had a Type 1 germination response pattern, which heretofore has not been reported in perennial Asteraceae. Achenes of Chaptalia nutans first germinated (to ≥ 10%) at 20/10 and 25/15°C and those of Hymenopappus scabiosaeus at 20/10°C, but with further loss of dormancy achenes of both species also germinated at 15/6, 30/15 and 35/20°C. Thus, achenes of these two species had a Type 3 pattern. This is the first report of perennials in any family with a Type 3 response pattern whose seeds come out of dormancy during summer. Presence of annual and perennial Asteraceae with Type 2 in temperate eastern North America and annual and perennial Asteraceae with Type 1 in southcentral Texas causes us to conclude that climate is more important than the type of life cycle in determining the type of germination response pattern.     

Effects of microhabitat,light and temperature on seed germination of a critically endangered Himalayan medicinal herb,Swertia chirayita: Conservation implications

Abstract

Swertia chirayita, a critically endangered medicinal herb, is being over-harvested in the wild. Understanding seed germination is a pre-requisite to ensure species conservation. The germination of seeds collected from six microhabitats was studied at 20°C, 25°C, and 30°C, both under a 14/10 h light/dark photoperiod and in continuous darkness. Two-way ANOVA indicated that microhabitat and temperature significantly affect seed germination, germination rate, germination recovery (GR), and GR rate. Overall, the seeds collected from under canopy showed a significantly (p < 0.05) higher germination than those from open habitats, at 20°C, 25°C, and 30°C (14/10 h light/dark photoperiod). Germination was negligible in continuous darkness but after transfer to a 14/10 h light/dark photoperiod, the seeds from under canopy significantly recovered at 20°C and at 25°C (p < 0.05), and showed the highest germination percentage compared to seeds collected from tree base, stump base, shrubberies, and grassy slope. Similarly, at 30°C, seeds from under canopy recorded the highest GR percentage. In general, seed germination, mean germination rate, seed GR, and GR rate were significantly greater (p < 0.05) at 25°C. Among the microhabitats tested, variation in GR rate was significant (p < 0.05). Seeds were confirmed to be positively photoblastic.     

SEED MORTALITY IN DAUCUS CAROTA POPULATIONS: LATITUDINAL EFFECTS

Daucus carota, a common herbaceous weed, grows over a wide latitudinal range in eastern North America. Viability and germination tests of mature seeds collected from 36° to 45°N were conducted to measure predispersal seed mortality. Viability and germination declined as latitude of the seed source decreased. Only 30–50% of the seeds from southern populations germinated owing to high embryo inviability and absence of embryos. Sixty to ninety percent of the seeds from northern populations germinated. Reciprocal planting of seeds in outdoor experimental plots at three latitudes and testing of seeds over two generations together showed that the environment in which seeds mature, rather than environmental preconditioning over generations or genetically-based differences among populations, explain this variation in germination ability. Within-latitude germination declined in experimental plots as population age of the seed source within latitudes increased. The data indicate that predispersal seed mortality can influence local population persistence and that seed mortality is an increasingly important factor in population regulation at the southern limit of the species’ range.     

Improving germination and vigour of aged and stored onion seeds by matriconditioning

Germination and vigour of accelerated aged (AA) and naturally stored onion seeds were examined. Accelerated ageing was conducted at 40 °C and 100 % relative humidity (RH). Non aged seeds were stored for 34 months at 3 or 15 °C and 40, 60 or 90 % RH. To restore seed viability, stored and aged seeds were matriconditioned with Micro-Cel E. A distinct loss of germination was observed after 5 days of accelerated ageing. Naturally stored seeds maintained high viability for 34 months, when stored at 3 °C and 40, 60 and 90 % RH or at 15 °C and 40 %. An increase of RH to 60 and 90 % at 15 °C caused loss of germination and vigour. Matriconditioning improved germination and increased endogenic ethylene release and in vivo ACC oxidase activity of both aged and stored seeds.     

Germination characteristics of the grass weed Digitaria nuda (Schumach.)

The effect of various pre-treatments and their interaction with temperature on cumulative percentage and the rate of germination were evaluated for Digitaria nuda. Stored and fresh seeds were pre-treated with either 0.02 M KNO₃, soaked in water for 24 h (priming), sterilized with 0.5% NaOCl or heat treated at 60 °C. Seeds were germinated at constant temperatures of 25 and 30 °C and fluctuating temperature regimes of 25/10 and 30/15 °C. The effect of pre-chilling on germination of stored and fresh seed was evaluated at 30/15 °C, and seed emergence in two soil types at different burial depths (0, 0.5, 1, 2, 3, 4, 5 and 6 cm) was also determined. The pre-treatment of stored seed with KNO₃ resulted in the highest germination percentage (100%), whereas the pre-treatment of fresh seed with water for 24 h gave the best germination (99%), at constant temperatures of 25 and 30 °C. Pre-chilling of seed increased germination by more than 30%. Emergence from clay loam soil was greater compared with the emergence from sandy loam soil. Total seedling emergence decreased exponentially with increasing burial depths with only 5% of seed germinating from a burial depth of 6 cm. Results from this study showed that germination requirements are species specific and knowledge of factors influencing germination and emergence of grass weed seed can assist in predicting flushes in emergence allowing producers to implement control practices more effectively.     

Seed Germination of a Halophytic Grass Aeluropus lagopoides

Aeluropus lagopoides(Linn.) Trin. Ex Thw. (Poaceae) is a perennialgrass distributed from coastal Sindh and Balochistan to salineflats of Punjab, Pakistan. Seeds collected from an inland populationofA. lagopoides located on the University of Karachi campuswere germinated under various levels of salinity (0, 100, 200,300, 400 and 500 m M NaCl) and temperature regimes (10/20, 15/25,20/30 and 25/35 °C) in a 12 h dark/12 h light photoperiod.Highest germination was obtained under non-saline conditions,and an increase in NaCl concentration progressively inhibitedgermination. Inhibition of germination was greater at coolertemperatures (10/20 °C) when no seed germinated above aconcentration of 300 m M NaCl. The germination response at moderatetemperatures (20/30 °C) was optimal, with 30% of seeds germinatingin 500 m M NaCl. The rate of germination decreased as salinityincreased. Germination rate was highest at 20/30 °C andlowest at 10/20 °C. Seeds were transferred from salt solutionsto distilled water after 20 d and those from high salinitiesrecovered quickly at warmer temperatures with an optimal responseat 20/30 °C. Copyright 2001 Annals of Botany Company Aeluropus lagopoides, germination, halophyte, Karachi, salinity, temperature     

Effect of salinity,temperature and hypersaline conditions on the seed germination in Limonium mansanetianum an endemic and threatened Mediterranean species

Abstract

Limonium mansanetianum is catalogued as critically threatened (CR) species and it is included in Valencian Catalogue of Threatened Plant Species. Limonium mansanetianum is a gypsicolous species, which only lives in a restricted area to south-centre of Valencia province (Spain). The species is a low-branched woody shrub with summer flowering. The influence of incubation temperature (10°, 15°, 20° and 25°/20?°C) and salinity (0%–3.0% NaCl) on seed germination of L. mansanetianum was studied. Best seed germination was obtained in distilled water controls. Seed germination decreased with an increase in salinity and few seeds germinated at 2.5% and 3.0% NaCl. Optimal temperature regime for germination was 15?°C where germination in 0.5% and 1.0% NaCl was not affected. Recovery and hypersaline conditions experiments showed that L. mansanetianum seeds displayed a greater tolerance to high salinity and temperature stress before germination.     

A study of the optimum drying conditions for cabbage seed following selection on the basis of a newly-emerged radicle

A series of experiments were carried out to study the effects of different drying regimes on the survival of newly-germinated (radicle emerged 0·5-1·5 mm through the seed coat) cabbage seeds and to establish a treatment for reducing the moisture content of these germinated seeds. A preliminary surface-drying step proved necessary to avoid seed agglutination during the main drying stage. Of the drying regimes compared both viability and vigour were most effectively maintained in air, conditioned to between 20 and 30°C and with 80% r.h., flowing through the seeds at 0·25 m s^-1. Under these conditions, the viability and vigour of newly-germinated seed was maintained during drying to an equilibrium moisture content of c. 14%. At this moisture content further radicle growth was prevented and seeds remained free-flowing and separate for sowing or for further treatment.