Comparisons of the use of pre-germinated,dry and pelleted seeds for block-raising of glasshouse lettuce

The use of pre-germinated seeds for establishing glasshouse lettuce in peat blocks was compared with dry and pelleted seeds. Sowing pre-germinated seeds gave between 1 and 6% higher seedling emergence than from pelleted seeds and between 1 and 3% higher emergence than from dry seeds. Seedling emergence was reduced from 100% to 56% when the seeds were covered with 5 mm of silver sand compared with no cover. Seedling emergence from seeds covered with Agrigel (sodium alginate) was reduced by 24% at a concentration of 0.25% and by 62% at 0.7% compared with no cover.Guar (a natural gum) and Laponite (a synthetic clay) gels also reduced emergence on certain occasions but not by as much as Agrigel. Satisfactory levels of emergence were obtained when seeds were sown into blocks having an inverted, cone-shaped depression for locating the seeds, but the seedlings showed poor root-hair development and had elongated hypocotyls. Normal seedling growth and high levels of emergence were obtained from the seeds sown into blocks having cylindrical holes 10 mm in depth and 5 or 10 mm in diameter. Pre-germinated seeds invariably emerged earlier than pelleted or dry seeds. At low propagating-temperatures (12.0°C maximum and 5.0°C minimum), emergence was 4 days earlier from pre-germinated than from dry or pelleted seeds and 2–3 days earlier at high temperatures (21.0°C maximum and 9.0°C minimum). Coefficients of variation of seedling weight at planting were lower from sowing pre-germinated than pelleted or dry seeds, but these differences were not evident at harvest.     

Priming and pre-germination of parsnip (Pastinaca sativa L.) seed

Seedling emergence and growth responses to priming seeds in polyethylene glycol solutions, to germinating them before sowing and to a combined priming and pre-germination treatment were examined in the field and growth rooms using several stocks of seed. Priming or priming and pre-germinating seeds of a slowly germinating stock improved the percentage seedling emergence compared with untreated and pre-germinated seeds. In rapidly germinating stocks all three seed treatments showed similar levels of emergence which were higher than those of untreated seeds. Both priming and pre-germinating seeds reduced the mean emergence time and, in general, the effect of the combined treatment was greater than either treatment alone. Priming alone generally had no effect on the spread of emergence time or on seedling or plant weight variability, but pre-germinating seeds increased variability, particularly in a slowly germinating stock. Priming seeds before pre-germinating them reduced this variability.     

The effects of pre-sowing seed treatments on the germination and emergence of lettuce seeds at high salt concentrations

Radicle emergence in lettuce seeds cultivar ‘Hilde’ was reduced by NH₄NO₃ above 8×10^?2M, while radicle extension was inhibited by 8×10^?2M NH₄NO₃ and no seedlings emerged. Inhibition of radicle emergence by 8 and 16×10^?2M NH₄NO₃ was prevented by soaking seeds for 4 h before sowing in a mixture of $\text{GA}{}_{\mathrm{<mtext>4</mtext><mtext>7</mtext>}}$ and kinetin+phosphate buffer, and was partially prevented by soaking them for 4 h before sowing in phosphate buffer. These treatments did not prevent inhibition of radicle emergence by 32×10^?2M NH₄NO₃, but seeds soaked in growth regulators or phosphate buffer before sowing and taken from this NH₄NO₃ solution after 7 days and washed to remove excess salt gave 45–52% germination compared with 12 % for untreated seeds. Pre-treatment of the seeds did not prevent the inhibitory effect of NH₄NO₃ on radicle extension. In field experiments seeds treated with growth regulators + phosphate buffer or phosphate buffer alone gave a higher final percentage emergence from soils given 125 kg N/ha than did untreated seeds.     

Effect of stratification-temperature,chemical treatments and seed coat on the growth of peach seedlings cultivar ‘Sharbati’

In order to obtain normal seedlings of peach cultivar ‘Sharbati’ before the commencement of winter, treatments with GA₃, thiourea and kinetin were given to seeds before stratification at 7°C, 10°C or 24°C. The seedlings raised from the treated seeds and after-ripened at 24°C were dwarf. The seedling growth was increased when the treated seeds were stratified at 10°C or 7°C and the stratification period was prolonged from 15 days to 75 days. 10°C stratification-temperature was better than 7°C. The seedling growth was improved when the seed coat was removed before the treatments. With respect to both seed types, 1000 mg/l GA₃ produced the tallest seedlings at all the after-ripening temperatures and during each stratification period. The next best treatment was 100 mg/l kinetin.     

More rapid and uniform germination of Cyclamen persicum L.

Two pre-sowing treatments are described which permit the initial germination processes to proceed but prevent the emergence of any radicles prior to sowing. Such treatments can result in a distinct reduction in the time between sowing and germination and in the length of the germination period. One method employs an aerated osmotic solution, here polyethylene glycol (PEG) ‘6000’ at a water potential of ?8 to ?11 bars at 15°C for 3–5 weeks. The alternative method in which a thermodormancy-enforcing temperature (25–30 °C) is substituted for the osmotic solution is less effective. For best effects, treated seeds should only be surface dried and sown immediately, although some of the effect persists on air drying. It may be necessary to calibrate each batch of seeds for the conditions which advance the germination process as far as possible without permitting actual germination during the treatment.     

The effects of heat treatment on hardseededness of serially harvested okra seed lots at optimum and low temperatures

A heat treatment of 50°C for 2 days increased both germination rate and capacity of serially harvested (36, 39, 43, 46, 50, 58 DAA) okra (Abelmoschus esculentus (L.) Moench cultivar Akköy) seeds. The more mature the seeds the better the response to treatment. Maximum advantage was obtained from seeds harvested 58 DAA, at which maximum hardseededness occurred and at an incubation temperature of 18°C as opposed to 25°C. Treated seeds of 58 DAA showed germination of 84 and 48% at 18 and 25°C, respectively. Eradication of hardseededness by the treatment was associated with an increased imbibition rate and electrical conductivity of steep water. The better results at 18°C indicate that the heat treatment can be used by commercial companies and individual producers for early sowings in order to obtain better seedling establishment.     

Promotion by 5-aminolevulenic acid of pepper seed germination and seedling emergence under low-temperature stress

The effects of incorporating 5-aminolevulenic acid (ALA) into the priming solution on low-temperature germination and emergence percentage performance of red pepper (Capsicum annuum cv. Sena) seeds before and after seed storage were investigated. Seeds were primed in 3% KNO₃ solution for 6 days at 25 °C in darkness containing 0 ppm, 1 ppm, 10 ppm, 25 ppm, 50 ppm or 100 ppm ALA. Following priming, seeds were either immediately subjected to germination and emergence tests at 15 °C or stored at 4 °C or 25 °C for 1 month after which they were subjected to germination and emergence tests at 15 °C. Priming pepper seeds in the presence of ALA improved final germination percentage (FGP) and germination rate (MGT) at 15 °C compared to non-primed seeds. The highest FGP was obtained from seeds primed in the presence of 25 ppm and higher ALA concentrations while the highest MGT was obtained from seeds primed in KNO₃ supplemented with 10 ppm ALA. Emergence percentages were the highest for the seeds primed in the presence of 25 ppm ALA and 50 ppm ALA while non-primed seeds had the lowest emergence percentage. Highest emergence rates (MET) and heaviest seedlings were also obtained from seeds primed in KNO₃ supplemented with 50 ppm ALA. Although all priming treatments improved germination and emergence performance of pepper seeds at 15 °C following 1 month of storage under two different temperatures, inclusion of 25 ppm and 50 ppm ALA into the priming solution resulted in higher germination and emergence percentages and faster germination and emergence compared to seeds primed in KNO₃ only and non-primed seeds. These results indicate that priming seeds in 25 ppm and 50 ppm ALA incorporated into the KNO₃ solution can be used as an effective method to improve low-temperature performance of red pepper seeds and that these seeds can be stored for 1 month at 4 °C or 25 °C and still exhibit improved germination and emergence performance at 15 °C.     

Fast germination of parsley seeds

The time from sowing to 50% radicle protrusion of parsley seeds (Petroselinum crispum L.) was about 1 month at 5°C and about 1 week at 15°C. Osmotic pre-treatment (“priming”) with a polyethylene glycol “6000” solution of ?12 bars water potential (302 g PEG “6000” per 1 kg distilled water) at 15°C for 3 weeks under aerobic conditions reduced this median radicle protrusion time at 15°C to 1 or 2 days for seeds which had been surface-dried after treatment, 2 or 3 days when they had been air-dried and stored for 1 week, and 3 or 4 days after 10 weeks' dry storage. The uniformity in germination time of an untreated seed population was usually good, and care was needed not to make this worse by “over-priming”. An appropriate pre-treatment could, however, slightly improve the uniformity. Germination percentage remained unaffected but the pre-treatment could appreciably improve the emergence percentage of seeds sown in wet soil. In a small-scale experiment out of doors, the weight of plants from certain seed treatments was significantly greater after 14 weeks' growth than that from untreated seeds.     

Seed germinability in Musa velutina Wendl. & Drude is markedly lowered by 1 week in dry-storage

SUMMARY

We investigated the effects of dry-storage of Musa velutina seeds on seed and embryo germination. Seeds were collected immediately after harvest and stored in dry vermiculite at 25°C, in the dark, for 0, 1, 2, or 4 months. The germinability of dry-stored seeds was assessed by incubation in vermiculite at 25°C for 4 months, with 75% [(w/w); –0.01 MPa] moisture content to promote embryo development in viable seeds. Seeds that had not been dry-stored and stored in vermiculite at 75% (w/w) moisture content for 4 months showed 90% germination by 20 d after sowing, but no seeds that had been dry-stored for longer than 1 month germinated. Seeds were also dry-stored at 25°C, in the dark, in Petri dishes for 0, 1, 2, 3, or 4 weeks after harvest and the embryos removed from these seeds were cultured on MS medium. All embryos that had been isolated from seeds at harvest (i.e., 0 weeks in dry-storage) germinated during embryo culture. However, embryos removed from seeds that had been dry-stored for 1 week showed a substantial decrease in both size and germinability. Seeds were also stored at different moisture contents for 4 months after harvest. No seeds that had been stored at 0% moisture content (i.e., dry) germinated, but > 85% of seeds stored at ≥ 25% (w/w) moisture contents germinated. Higher moisture contents increased the uniformity of seed germination, showing that M. velutina seeds rapidly lose their germinability through dehydration, indicating that they are sensitive to desiccation.     

Temperature requirements for the germination of olive seeds (Olea europaea L.)

Summary

Olive seeds cv Chondrolia Chalkidikis were subjected to temperatures of 5°, 10°, 15°, 20°, 25° and 30°C for one, two or three months, and were then transferred to 20°C. Exposure to 10° and 15° for one month or more caused higher emergence percentages compared to that at a constant 20°C. The highest germination rate was observed when seeds subjected to 10°C for one month were then transferred to 20°C. Seeds at 5°, 25° and 30°C did not germinate while being held to these temperatures; even when transferred to 20°C the percentage and rate of emergence were lower than those of seeds held at constant 20°C. In another experiment, in which seeds were subjected to 10°C for 0, 2, 4, 6 and 8 weeks before being transferred to 20°C, it was found that four weeks exposure to 10°C was near optimal. Emergence percentages of seeds at constant 10°C or at diurnally alternating temperatures of 10° for 16 h/20° for 8 h were high and equal (92%), but emergence in the latter treatment was slower. Alternating 10° with 25°C resulted in a 95% reduction of the emergence percentage. Transferring seeds immediately after chilling at 10°C for three or four weeks to 25°C, partially reversed the effect of the low temperature. However, the chilling effect could not be reversed when the seeds were subjected to 10°C for five weeks.     

The influence of temperature on growth,bolting and yield of chicory cv. Rosso di Chioggia (Cichorium intybus L.)

Summary

This work on spring-grown chicory shows the influence of temperature from the first stages of development on the subsequent performance of the plant. Temperatures of 20-26°C from sowing to emergence proved most suitable for emergence. Faster growth of seedlings in the following 5-10 weeks was also observed. Moreover, temperatures of about 20°C during emergence proved sufficiently high to reduce the incidence of bolting, and increased marketable yield. These effects on bolting and yield were more evident after early transplanting. A strong reduction in bolting was also observed by delaying transplanting, but this was at the expense of early production. Postponing transplanting improved the number of leaves per plant and the average weight of the heads. Exposure of the seeds to 0°C for two weeks prior to sowing allowed faster emergence of seedlings compared with that of seedlings of seeds exposed to 20, 30 and 40°C. Low temperature also influenced the subsequent development of the plants, favouring their growth in the first three months of the cycle.     

Gibberellin-like stimulation of celery (Apium graveolens L.) seed germination by N-substituted phthalimides

Thermodormancy of celery seeds incubated in the dark at 22°C was alleviated by two N-substituted phthalimides to the same extent as that normally achieved with a mixture of the gibberellins A₄ and A₇. As previously demonstrated with GA₄₊₇, the highly dormant cultivar ‘Lathom Blanching’ responded more to phthalimides in the presence of cytokinin, whereas ‘Florida 683’ required no cytokinin to elicit the maximum response to phthalimide treatment. Seed-soak treatments with either N-substituted phthalimide improved both the rate of germination and the percentage seedling emergence of both cultivars sown in compost under glasshouse conditions.     

Soil seed banks are short-lived and triggered by the first effective rainfalls in the vacant lots of Santiago,Chile

We studied the temporal variation of the soil seed banks in the urban lots of Santiago, Chile. As most of the plants that emerge from the seed banks in lots are also found in open habitats and are easily germinable, we hypothesize that the seed banks in lots are highly dynamic and short-lived, with the bank depleted every year during the germination season to be reloaded with new seeds during the next seed dispersal period. In each 20 lots for two year (2017 and 2018), 9 soil samples were collected. These samples were obtained from three sampling points randomly distributed across the plots. The seed bank was estimated by seed germination in soil samples placed in plastic trays. The samples of all the lots were stratified at 2 °C by 3 months before sowing. In order to record the seed persistence, soil of three lots watered in 2017 for six months were dried and maintained under dark and non-watered conditions until re-sowing in autumn 2018. To determine if the seeds present cold-associated germination triggers, soils of five lots were maintained under dark conditions for 3 months (soils without cold stratification) for comparison with soils with cold stratification of the same lots. The above-ground plants were recorded in all lots for both years. Forty plant species were recorded in soil bank. The total emerged seedling densities ranged between 7,944 (2017) to 3,700 seedlings m^-2 (2018). Species per lot varied between 17 and 7 during 2017, and between 14 and 3 during 2018. In five lots, seedling densities were not statistically different between cold stratified soil at 2 ° C and non-stratified. In three lots with re-sown soil, seedling density of the first sowing (4,096 seedlings m^-2) was significantly higher than second sowing (201 seedlings m^-2). Thirty-seven plant species were recorded in the above-ground vegetation during 2017 and 42 species in 2018. Species frequency of the seed bank was positively correlated with species frequency of above-ground vegetation. Concluding, the bank is highly dynamic, short-lived, and is depleted every year during the germination season, which begins with effective rainfalls, would be reloaded with seeds during the seed dispersal period.     

Low temperature and gibberellic acid stimulation of germination in Sambucus caerulea Raf

Sambucus caerulea (elder) seeds did not germinate after 4°C cool treatments for up to 30 days, when monitored for a further 30 days at 21°C. When seeds were soaked for 24 h in gibberellic acid (GA₃) prior to and during cold treatment, germination percentage depended on GA₃ concentration and duration of cold treatment. The highest germination percentage was 55 (1000 mg l⁻¹ GA₃ for 30 days at 4°C). When seeds were treated with ethephon at 0, 100 or 1000 mg l⁻¹, no germination was recorded after a subsequent 30-day 4°C treatment. Ethephon added to GA₃ gave a strong interaction, leading to further promotion in germination. Optimal germination was obtained after 1000 mg l⁻¹ GA₃ and 100 mg l⁻¹ ethephon for 30 days at 4°C (69%).The addition of ethanol, acetone, dimethyl sulfoxide or polyethylene glycol to the GA₃ soak as infusion agents either reduced or did not change the germination percentage.     

Analysis of the Growth and Yield of Overwintered Onions

The growth of a number of onion cultivars sown on different dates during late summer in several years was assessed by regular sampling. The growth during the winter of five different winter-hardy cultivars was very similar, whereas that of Rijnsburger Bola, a cultivar normally sown in spring, was clearly slower. Sowing date was shown to affect final yield through its effect on overwintering size, which in turn influenced bulb size at harvest, the proportion of plants which bolted and the extent of winter losses. During the winter months the rate of leaf initiation appeared to be decreased to a lesser extent than the growth in dry weight, which itself was decreased less than growth in leaf area. The growth of the winter-hardy cultivars from all sowing dates and seasons was well summarized by a single linear relationship between the logarithm of plant dry weight and the accumulated day-degrees between 6° and 20°C from the day of seedling emergence. Using this relationship together with temperature records from past years it was possible to estimate the best average sowing date and the year-to-year variation in optimum sowing date. This approach may prove useful in predicting optimum sowing dates for other localities from past weather records.     

The use of chilling and chemical treatments to promote rapid germination of strawberry achenes

In the absence of special pre-treatments germination of achenes of three octoploid varieties of strawberry at 20°-25° C. was light-dependent and very variable. Values seldom exceeded 30% and were frequently much lower. Treatments with thio-urea and gibberellins A₃ and A₄ produced variable results, but failed to secure useful increases in percentage germination rates.

Pre-chilling the imbibed achenes at 2° C. for six to eight weeks promoted germination to about 80% within 14 days of transfer to warm conditions.

After chilling treatments the achenes eventually became largely independent of light for germination, but longer chilling periods were required for equivalent performance of dark-grown, compared to light-grown, achenes.     

Methods to overcome seed dormancy in Echinacea angustifolia DC

Some factors (light, prechilling, gibberellic acid, ethylene) affecting germination of seeds of Echinacea angustifolia DC. were investigated. Without any pretreatment, the seeds germinated better in darkness than in light, however, percentages germination were low in both cases. GA₃ did not increase germination in light. Prechilling for 7–15 days in light or in darkness hardly affected percentage germination but significantly increased the rate of germination. Ethephon during prechilling resulted in a large increase of percentage and rate of germination in light, but had hardly any effect on germination in darkness. The results showed that a prechilling treatment for about 11 days at 5°C in a 1 mM ethephon solution in continuous light, followed by a 2-week germination period in light (24 h per day) at 20/30°C, can induce >90% seed germination in E. angustifolia. The prechilling treatment in ethephon also increased the rate of germination.     

The effect of seed treatment on the germination and early growth of Euterpe edulis (family Palmae)

The germination rate of palm seeds can be improved by pre-treatment of the seed. Several methods proved effective for Euterpe edulis seed, but sulphuric acid immersion and hydrogen peroxide leaching treatments both decreased emergence of germinated seedlings and restricted plant growth up to 6 months after germination.The best overall results in germination and subsequent seedling development were from seed leached in water for 72 hours at 30°C. This treatment can be related to the natural conditions encountered by the seed in the highly leached soils of a tropical rain forest.     

Effects of Pre-Stratification Storage Conditions on Black Walnut Seed Post-Stratification Germination Capacity

The objective of this work was to quantify changes in the germination capacity of Juglans nigra seeds following storage and then artificial stratification. Seeds were stored at 5 and –20 °C under 5% and 14% internal moisture content (IMC) for 0, 8, 10, and 12 months under conditions with oxygen or under vacuum. Germination percentage (GP) was affected by storage temperature, IMC, and storage period. Seeds stored with 5% IMC succeeded in germinating regardless of the temperature. Seeds stored with 14% IMC did not germinate (–20 °C) or germinated during storage (5 °C). The GP was reduced with the time of storage in seeds at –20 °C and 5% IMC and this effect was avoided in storage under vacuum. In conclusion, the germination capacity of black walnut seeds did not change for up to 12 months at low above-zero temperature and low IMC (5 °C, 5% IMC), being the most cost-effective alternative for long-term storage of black walnut seeds in commercial nurseries. Vacuum storage avoided the decrease of around 50% in average germination capacity of seeds stored for a year at –20 °C.     

Seed germination of seven pepper cultivars at constant or alternating high temperatures

Summary

Seeds of seven pepper (Capsicum annuum L.) cultivars (Anaheim TMR 23, California Wonder 300, Coronado, Jalapeno M, Ma Belle, Mercury, and Yolo Wonder B) were germinated at constant day and night temperatures of 25,30,35 and 40°C or at alternating temperatures of 40/25,40/30 and 40/35°C for 14 days. Germination percentages and rates were similar at 25 and 30°C. Largest differences in cultivar responses occurred at 35°C where germination percentages ranged from 24 to 96%, and rates, calculated as summation of the number of seeds germinated on a given day divided by day number, varied from 3 to 26 (theoretical maximum value of 100). At 40°C, germination percentages were less than 5% and rates were less than one for all cultivars. Cultivars with the most heat tolerance were ‘Mercury’ and ‘Yolo Wonder B’. At alternating temperatures, germination percentages and rates were higher than those at constant 40°C. The increases were greatest when the temperature was lowered by 15°C (40/25°C) and least when temperatures were lowered by 5°C (40/35°C). Tetrazolium tests showed that a large percentage of the ungerminated seed was still viable from the highest temperature. At lower temperatures, fewer ungerminated seeds were viable with no viable ungerminated seeds from the lowest temperature.