Stratified Seeds Research Articles

The Light Requirement for Germination of Aster Pilosus Seeds: Temporal Aspects and Ecological Consequences

(1) At maturity in autumn, Aster pilosus seeds were conditionally dormant and germination was 88-95% in light at 25/15, 30/15 and 35/20 'C. There was little or no germination in light at 15/6 or 20/10 ?C or in darkness at any thermoperiod. (2) Most of the seeds were dispersed in December and January, but some were still on the plants in April. Seeds collected from plants in late February were non-dormant; 99-100% germinated in light and 17-47% in darkness at all thermoperiods. (3) Imbibed seeds exposed to light for 4 weeks at the simulated November temperature (15/6 IC) or to light for 1-6 weeks during the first half of winter (12 weeks at 5 OC), or both, subsequently showed only 0-30% germination in darkness at the simulated April temperature (20/10 OC). However, of imbibed seeds exposed to light for 1-6 weeks during the second half of winter 0-55% germinated at 5 0C, and germination percentages increased to 87-96% in darkness after they were transferred to 20/10 ?C. (4) In stratified seeds given a single 8-12 hour exposure to light, subsequent germination was 75% in darkness at 20/10 OC. Seeds at a 14-hour daily photoperiod had 100% germination in 8 days, but those in constant darkness only reached 1% in 15 days. (5) Apparently, only after they become non-dormant during winter can seeds be light-stimulated to high germination percentages in darkness in spring. Thus, seeds that become buried in autumn or early winter should not germinate in spring, whereas if no other factors of the soil environment besides darkness prevent germination, seeds that become buried in late winter should germinate in spring.

Germination Ecophysiology of Hydrophyllum appendiculatum, a Mesic Forest Biennial

In north central Kentucky, seeds of the mesic forest biennial Hydrophyllum appendiculatum Michx., are innately dormant at maturity in June. Under natural and simulated seasonal temperature changes, dormancy break occurred in two stages. Root dormancy was broken by high summer temperatures, and shoot dormancy was broken by low winter temperatures. Consequently, roots emerged from seeds during autumn, and cotyledons emerged the following spring. A 90-day warm (30/15 C) stratification treatment broke root dormancy, but the roots emerged only after transfer to lower temperatures. After the warm stratification treatment, roots emerged from 93, 73, 6 and 9% of the seeds incubated at 5, 15/6, 20/10 and 30/15 C (12/12 hr), respectively. Zero, 28, 56 and 84 days of cold (5 C) stratification of seeds with emerged roots resulted in 9, 21, 49 and 82% cotyledon emergence, respectively, at 20/10 C. Thus, H. appendiculatum exhibits a type of morpho-physiological dormancy known as epicotyl dormancy. Although many seeds germinate the first year, others remain dormant and germinate in successive years until the fourth season after ripening.

GERMINATION ECOPHYSIOLOGY OF HYDROPHYLLUM APPENDICULATUM, A MESIC FOREST BIENNIAL

In north central Kentucky, seeds of the mesic forest biennial Hydrophyllum appendiculatum Michx., are innately dormant at maturity in June. Under natural and simulated seasonal temperature changes, dormancy break occurred in two stages. Root dormancy was broken by high summer temperatures, and shoot dormancy was broken by low winter temperatures. Consequently, roots emerged from seeds during autumn, and cotyledons emerged the following spring. A 90‐day warm (30/15 C) stratification treatment broke root dormancy, but the roots emerged only after transfer to lower temperatures. After the warm stratification treatment, roots emerged from 93, 73, 6 and 9% of the seeds incubated at 5, 15/6, 20/10 and 30/15 C (12/12 hr), respectively. Zero, 28, 56 and 84 days of cold (5 C) stratification of seeds with emerged roots resulted in 9, 21, 49 and 82% cotyledon emergence, respectively, at 20/10 C. Thus, H. appendiculatum exhibits a type of morpho‐physiological dormancy known as epicotyl dormancy. Although many seeds germinate the first year, others remain dormant and germinate in successive years until the fourth season after ripening.

Germination Speed as a Predictor of Nursery Seedling Performance

Abstract Although they are not fully satisfactory, laboratory germination percentages are still better predictors of nursery-tree yield for both loblolly (Pinus taeda L.) and slash (Pinus elliottii Engelm.) pine seeds than any other means now available. Germination values, which combine both speed and completeness of germination, improve the predictability of nursery performance only in slowly germinating lots. Analyses of the reasons for better nursery growth of seedlings from stratified seeds reveal that under less favorable conditions they germinate faster than unstratified seeds. When equal-aged germinants from similarly-sized stratified and unstratified seeds are planted at the same time, seedling development is essentially the same. Seedlings from large-sized seeds (half-sib lots) did grow larger over a 10-week period than those from small-sized seeds.

Seed Generation of Eucalyptus pauciflora Sieb. ex Spreng. From Low and High Altitude Populations in Victoria

Seeds from two subalpine populations of E. pauciflora stored for 1 year were completely dormant and required stratification to induce germination. Fresh seeds from the same populations were partially dormant. Seeds from a third subalpine population whether fresh or stored were only partially dormant. Seeds from two lowland populations were not dormant, although stratification did reduce the time taken to complete germination. The optimum germination temperature for all populations was near 20°C. Temperatures above 25°C induced a secondary dormancy in stratified seeds from two of the subalpine populations.

Arabinogalactan-proteins from douglas fir and loblolly pine

Arabinogalactan-proteins, identified as β-lectins by their precipitation with β-glucosyl Yariv antigen, were isolated from the dry seeds, stratified seeds, 2-week-old seedlings, 2-month-old seedlings, 2-year-old saplings, and 1-month-old callus of loblolly pine and Douglas fir. Two-way analyses of variance revealed that certain β-lectin parameters differed significantly from one another depending on the species and developmental state of a sample's origin.

A Technique for Determining Quantitative Expressions of Dormancy in Seeds

A method of quantifying the heterogeneity of dormancy within seed populations is described. The method compares germination responses of unstratified and stratified seeds of Pinus taeda L. (loblolly pine). Mathematical functions were fitted to cumulative germination curves of unstratified and stratified seeds and functions were integrated to determine areas beneath respective curves. The area between respective curves was calculated by difference and was considered to be a measure of dormancy within seed lots. The method may be used to help identify various controls of seed dormancy.

Germination and Establishment of Prostrate Spurge (Euphorbia supina)

Germination of prostrate spurge (Euphorbia supinaRaf.) seeds collected in August, September, October, and November 1977 at Riverside, California was 53, 30, 18, and 16%, respectively. Stratification of seeds collected in August, September, and October at 5 C for 3 weeks or more increased germination to 70 to 80%. Prostrate spurge seeds germinated at constant temperatures of 20 to 40 C, with optimum temperatures of 25 to 30 C. Maximum germination occurred under alternating temperatures with a high temperature of 30 to 35 C and a low temperature of 15 to 25 C. Germination in the dark was much lower than in the light. Seedling establishment of seeds collected in August sown at 0.0- to 0.5-cm depths was 30 to 35%, but establishment from 2 cm declined to near 0%. Light intensity did not affect the number of seedlings established, but the seedlings established were larger under higher light intensities.

Germination of embryos from stratified and non-stratified seeds and growth of apple seedlings (Malus domestica Borkh cv. "Antonówka")

The germination of whole seeds, the seeds without coat and isolated embryos of apple cv. "Antonówka Zwykła" after 90 days of cold-stratification was compared with the germination of embryos isolated from non-stratified seeds. They were germinated under 16hrs during a day at temperature 25°C and 20°C during the night. It has been found that after 2 weeks whole stratified seeds germinated in 5 per cent, seeds without coat in 25 per cent and isolated embryos in 98 per cent. Isolated embryos from nun-stratified seeds, after 2 weeks, germinated in the range from 75 to 88 per cent. The results indicate the similar germination ability of embryos isolated from nun-stratified seeds. The seedling populations obtained from embryo's stratified and non-stratified seeds were fully comparable and they evaluated: 1) a wide range of individual differences within population, 2) a similar number of seedlings in each class of shoot length, 3) a similar morphological habitus in each class of shoot length, 4) a similar fresh leaf weight and whole plant increment.

Germination of red alder (Alnusrubra) seed from several locations in its natural range

Germination tests were carried out on stratified, presoaked, and untreated seeds of red alder (Alnusrubra Bong.) collected from several locations throughout its range. Dormancy was not a significant factor in preventing germination of untreated seeds with one exception. Germination of untreated seeds, except those from the provenance showing dormancy, and of treated seeds of all provenances was relatively high and showed few differences between provenances. There were more pronounced differences in seed vigour, as measured by germination value.

Changes in phenolic acids and abscisic acid in sugar pine embryos and megagametophytes during stratification

The phenolic acids and abscisic acid (ABA) of sugar pine (Pinus lambertiana Dougl.) embryos and megagametophytes, separated by high‐pressure liquid chromatography, were analyzed during 90 days stratification of the seeds. The phenolic acids occurred mainly as glycosides. Following hydrolysis, the majority of phenolics present could be identified as common benzoic and ciranamic acid derivatives. Levels of phenolic acids were relatively low in dormant seeds, but increased substantially in the embryos during stratification at 5°C, particularly cinnamic acid, p‐coumaric acid, ferulic acid, and one unknown. This active synthesis during stratification did not support an inhibitory function for phenolic acids. During stratification at 5°C, changes in ABA levels in both tissues followed a triphasic pattern, with no loss during the first 30 days, a significant decrease the second 30 days, and a lesser decrease the last 30 days. Loss of ABA from moist seeds at 25°C occurred three times as rapidly, so that by 30 days the ABA level of these seeds was equivalent to that of seeds stratified 90 days at 5°C; however, dormancy was not alleviated at 25°C. Application of exogenous ABA (10−7 to 10−4M) to stratified seeds did not significantly reduce germination. Together, the above results did not support a primary role for ABA in the maintenance of dormancy in sugar pines.A correlated increase in phenylpropanoid metabolism and respiratory capacity with increased germinability during stratification suggests that loss of dormancy may be more closely dependent on increased levels of growth promoters or shifts in metabolic pathways.

Respiratory changes with stratification of pear seeds

Experiments on the stratification of seeds of pear (Pyrus communis cv. Bartlett) indicate that there is a progressive increase in respiratory capacity, with about a three‐fold increase developing during a 30‐day stratification period. Evidence is presented suggesting this increase in respiratory capacity occurs in the cytochrome oxidase pathway and not in the alternative pathway of respiration. The increase is much less pronounced if the seeds are held at 25°C rather than at 6°C. The seed coat serves as a barrier to the expression of the increased respiratory capacity.

The development of photosynthetic light reactions in cultured apple embryos in relation to their embryonal dormancy

The development of photosynthetic light reactions (photoreduction and photophosphorylation) was studied in cotyledons of cultured embryos isolated from stratified and non-stratified apple seeds (Malus domestica Borb. cv. Antonówka). The results obtained show the presence of an energy transfer inhibitor in the cotyledons of the stratified embryos.

Role of the Various Seed Parts in Peach Seed Dormancy and Initial Seedling Growth

Abstract Cold requirement for germination of excised ‘Kakamas’ peach (Prunus persica (L.) Batsch) embryos was satisfied after 2 weeks at 4.4°C; embryos with testas intact required 4 weeks, while seeds with intact endocarps required 12 weeks stratification. Leaching of unstratified excised embryos stimulated germination. The endocarp affected germination by delaying water uptake. Supplying additional O2 during stratification or germination of seeds with intact endocarps did not improve germination. Cracking the endocarps stimulated germination of stratified seeds, but sealing the cracks with lanolin paste prevented this effect. The endocarps may interfere with the leaching of inhibitors from the testa and embryo. Initial seedling growth of embryos with or without testas increased linearly with increasing time of stratification in terms of shoot length, dry weight of shoots and leaves, dry weight of roots and leaf area, length and width. Seedlings arising from embryos with intact testas were taller and had a greater dry mass of shoots, leaves and roots compared to seedlings arising from embryos without testas.

The effect of stratification on the endogenous levels of gibberellins and cytokinins in seeds of douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) and sugar pine (Pinus lambertiana Dougl.)

Abstract Seeds of Douglas‐fir and sugar pine which had been exposed to various periods of moist chilling (stratification) were extracted and bioassayed for gibberellin and cytokinin activity. In Douglas‐fir a peak of gibberellin activity increased progressively during stratification and was seven times higher after 7 weeks, but declined subsequently. No change in the level of cytokinin activity was observed during stratification. However, a slight increase (1.7‐fold) occurred in stratified seeds placed at 22°C for 3 days.In sugar pine a high level of gibberellin activity, approximately 20‐fold higher than in unstratified controls, was present in extracts of seeds which had been stratified for 8 weeks. After 10 weeks of stratification cytokinin levels had increased approximately 200‐fold. Four cytokinin‐like substances were detected in seeds. Three of the substances are similar in their chromatographic properties to zeatin glucoside, zeatin riboside and zeatin, respectively. Both gibberellin and cytokinin activity declined rapidly after reaching maximum levels.In seeds with the coats removed, germination was rapid and complete in the absence of stratification. Prior to radicle emergence in coatless seeds cytokinin activity increased to a maximum (approximately a 1‐7‐fold increase) within 24 h. Significant levels of gibberellin‐like substances were present after 8 h. Gibberellin activity could not be detected in coatless seeds which were imbibed in AMO‐1618, and germination was inhibited significantly.

Effect of stratification temperature, stratification period and seed coat on seed germination of peach cultivar ‘Sharbati’

Freshly harvested seeds of peach cultivar ‘Sharbati’ were found to be dormant and did not germinate at all. A specific low-temperature stratification treatment was required to overcome seed dormancy. 10° C stratification was found to be the best for breaking seed dormancy. Increased seed germination was recorded when the seeds were after-ripened without seed coats as compared to the seeds after-ripened with seed coats. There was no further increase in germination when seeds without seed coats were stratified beyond 60 days at 10° C, while a significant increase was recorded up to 75 days of stratification in the case of seeds with seed coats. Unstratified seed coats, soaked in water for 72 h, leached out a water-soluble inhibitor, which could suppress the germination of stratified peach seeds without seed coats. When this leachate was bioassayed by a cress-seed germination test, it showed the presence of an inhibitor at Rf 0.7-0.9. Hence, delayed germination of seeds with seed coats may be due to the presence of an inhibitor in seed coats.

Seedling Development in Peach, Prunus persica (L.) Batsch. II. Effects of Plant Growth Regulators and Their Possible Role

Treatment of peach embryos from partially stratified seeds with abscisic acid (ABA) inhibited germination and promoted the production of leaf lesions, responses which are typical of testa presence. A period of water stress during germination also promoted lesion production. Neither testas nor ABA stimulated lesions on seedlings from 25°C-stratified seed, but mixtures of ABA and GA*3 were synergistic in promoting lesions; at the same time ABA and GA3 had opposite effects on germination and stem elongation, and mixtures had intermediate effects. Evidence was obtained for effects attributable to a balance between GA and ABA. Other inhibitors and promotors had no effect on lesions. The results from excision and substitution experiments permit an explanation of the effects of stratification in terms of three events: (a) a decrease in inhibitor activity in the testa; (b) an increase in gibberellin activity in the epicotyl; and (c) diffusion of inhibitor to the epicotyl via the radicle when the seed is returned to warm conditions.

Phloridzin transformation and accumulation during the stratification of apple seeds and the culture of isolated embryos

Phloridzin level and phloridzin β-glucosidase activity were estimated during apple seed cold stratification and during the culture of apple embryos isolated from seeds after different times of stratification. Both these factors were found to increase parallel to the progress of stratification as well as to the increasing ability of seeds/embryos to germinate. However, in the seed coats phloridzin dissappears during the progress of stratification despite the increasing β-glucosidase activity. Phloridzin formation in the embryos is postulated to be under light and gibberellin control, when isolated embryos germinate, and under temperature and gibberellin influence during the cold stratification of the seeds. The same factors control β-glucosidase activity development, which is also stimulated by the substrate itself. It is postulated that phloridzin accumulation and its glucosidase activity are indirectly related to the after-ripening process and directly to the germination of the embryos.

‘Haggith’ Apricot: Rootstock Seed Source1

Abstract ‘Haggith’ (Prunus armeniaca L.) is a new apricot cultivar introduced in 1974 as a seed source for apricot rootstocks. Trees of ‘Haggith’ are cold hardy, consistently productive, self-fertile and disease tolerant. The seeds of ‘Haggith’ germinate readily as fall planted pits or as spring planted stratified seeds. ‘Haggith’ seedlings are quite uniform in the nursery row, attain buddable size by August and are compatible with a broad range of scion cultivars. Scions on ‘Haggith’ seedlings appear to be comparable in vigor, precocity and disease response with those on seedlings of ‘Alfred’ or ‘Morden 604’. However, there is a tendency for scions on ‘Haggith’ seedlings to have wider crotch angles, a more spreading growth habit, and slightly higher yield than on ‘Alfred’ seedlings. The ‘Haggith’ seedling rootstock is being introduced to meet the need for a reliable, cold hardy rootstock for apricot. ‘Haggith’ is not recommended as a scion variety.

The Absorption of Fenitrothion During Germination of Stratified and Nonstratified White Pine Seeds and Identification of Metabolites Formed

White pine seeds, P. strobus were treated with a 1.5 × 10−4 M solution of fenitrothion, 0,0-dimethyl-0-(4-nitro-3-methyl-phenyl)-phosphorothioate. The seed coat, endosperm, and embryo were monitored for residues of the insecticide and metabolites during germination and early seedling growth. Absorption and accumulation of fenitrothion, and accumulation of fenitro–oxon, and S-methyl fenitrothion were demonstrated in the endosperm and embryos of germinated seeds and seedlings. Neither the parent compound not its metabolites adversely affected the later development of the pine seedlings.