Not all leguminous seeds are equally long-lived, for example Koompassia malaccensis seeds have thinner seedcoats and deteriorate more rapidly in storage than species such as Parkia javanica , and they need no pretreatment to overcome seedcoat dormancy Sasaki a. Many species in important genera of forest trees fall into this group, e. Pinus , Picea , Eucalyptus. The majority of species can be stored for 10 years at room temperature with relatively little loss of viability Turnbull f.
Both E. In Thailand seeds of P. Considerably longer periods have been recorded for some species of pine e. Tectona grandis is an orthodox tropical broadleaved species Barner b but, since it produces good seed crops in most years, there has been little stimulus to investigate optimum conditions for long-term storage Schubert According to evidence summarized by Bowen and Whitmore , most Agathis spp.
For example, an appropriate treatment of A. A australis seed is inherently longer lived than A. Initial trials with the tropical A. However, later trials were inconsistent and less successful. With tropical species, it is likely that handling between collection and despatch and the largely uncontrollable conditions of air transit are more critical than in the easier temperate or subtropical species. Orthodox species which rapidly lose viability unless they are given the optimum treatment include species in the mainly temperate genera Populus , Salix and Ulmus. Many of these lose viability within a few weeks under natural conditions or if stored in ambient conditions of temperature and humidity, but can be stored for months or years if maintained at low temperature and low moisture content.
In the tropics Aucoumea klaineana is a good example of an orthodox species which is short-lived under ambient conditions. There is some indication that a further reduction of MC will conserve viability even better. Some species may need special treatment to prolong viability for more than a few months. It is then suitable for sowing because such storage conditions constitute a suitable pretreatment to break dormancy. This technique has been successfully applied on a large scale 17 tons of beechnuts from 51 different sources in France.
Germination has been maintained over periods of 4 to 6 years Muller and Bonnet-Masimbert Where storage conditions leave much to be desired, the longevity of orthodox seeds without hard coats can be expected to be much inferior to the hard-coated species. The nearer that conditions of storage approach the ideal for a given non-hardseeded species, the less the difference between its longevity and that of a hardseeded species.
Recalcitrant seeds include a number of large seeds that cannot withstand appreciable drying without injury; it is of interest that the overwhelming majority of recalcitrant species listed by King and Roberts are woody. Temperate species such as Quercus and Castanea are commonly stored moist only for short periods over winter.
Reduction of storage temperature to near freezing will prolong longevity. It is important to allow free entry of oxygen and this is ensured by inserting several strips of cardboard at intervals between the lid and the edge of the can. There may be possibilities of storing seeds after emergence of radicles see p. For A. Most short-lived recalcitrant tropical species are constituents of the moist tropical forests, where conditions conducive to immediate germination high humidity and high temperature are prevalent throughout the year.
Typical genera are Hevea , Swietenia , Terminalia and Triplochiton , as well as a number of Dipterocarp genera such as Dryabalanops , Dipterocarpus and Shorea and some species of Araucaria. Azadirachta indica seeds also have a short period of viability, although the species occurs in dry, not moist, tropical forests and it is not clear whether it is a genuine recalcitrant or simply a short-lived orthodox species. Orthodox and recalcitrant species sometimes occur within the same genus.
In Acer and Ulmus , genera in which both orthodox and recalcitrant seed behaviour occur, the distinction in North American species is clearly between spring- and fallseeders. Their seeds are not dormant, and their storage behaviour is clearly recalcitrant. Other Acer species have fall-maturing seeds, which are dormant and orthodox in nature at maturity. The same occurs in Ulmus. Seeds of U. In Araucaria , A. In Queensland seeds of A. At the lower temperatures of The rate of viability loss at the higher storage temperatures varied from provenance to provenance, but all stored better at the lower temperatures.
Storing Seeds: How to Preserve Seeds for Years | Epic Gardening
Later trials with Papua New Guinea A. Arentz found that high viability of A. Placing the seed in one polythene bag of 25 microns thickness inside a second bag is effective in maintaining viability. The double thickness of polythene maintains a high MC but allows for some exchange of oxygen which is necessary to preserve viability of A. In some tropical species, seeds are quickly killed if temperature is reduced too low, just as they are quickly killed if MC is reduced too low.
This compares with a normal seeding periodicity of several years in most dipterocarps, so there is no possibility as yet of conserving seeds in a viable condition from one good seed year to the next. Unlike orthodox species, in which viability is best preserved by maintaining a minimal respiration rate, it appears that active respiration is necessary to survival of seeds of most recalcitrants.
Thus damage to recalcitrant seeds has been reported not only from inadequate MC and too low a temperature but also from lack of oxygen e. Whereas some temperate recalcitrant species have been stored successfully for several years, seed longevity in tropical recalcitrants can be measured in days or weeks. The amount of research on tropical species is still small, especially on forest species, and it is possible that seed longevity could be prolonged beyond a few weeks if the best combination of seed maturity, speed, conditions and degree of drying, and most suitable storage temperature could be determined for each species.
King and Roberts suggest a research strategy. Even in ideal storage conditions seed will soon lose viability if it is defective from the start. Factors to be considered are:. Seed maturity. Fully ripened seeds retain viability longer than seeds collected when immature Stein et al. Certain biochemical compounds, essential for preserving viability, may not be formed until the final stages of seed ripening. These include dormancy-inducing compounds in certain species, and dormancy is sometimes associated with seed longevity. In a few species e. Gingko biloba , Fraxinus excelsior , seed embryos are underdeveloped when the seed is shed.
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Maturation of these embryos is necessary before sowing but need not be done before storage. For details of treatments see p. Parental and annual effects. In seed harvest, quantity and quality often go together. The percentage of sound seeds in a high-yielding mother tree is usually higher than in one with a poor crop. Similarly, a given mother tree will have a higher percentage of sound seeds in a good crop year than in a poor one. Collection from high-cropping mother trees in a seed year is likely to yield seeds with the best longevity in storage. Freedom from mechanical damage.
Seeds damaged mechanically in extraction, cleaning, dewinging etc. The danger is greatest for species which have thin or soft seedcoats. Excessive heat during extraction or drying also damages seed. Care should be taken to use the minimum times, lowest temperatures and minimum machine speeds necessary during the preparation of seed for storage Stein et al. In some species, damage during dewinging may be reduced by partly restoring the moisture content between extraction from cones and dewinging, since moist seeds suffer less mechanical damage than dry ones Nilsson , Barner b.
Freedom from physiological deterioration. Poor handling in the forest, during transit or during processing causes physiological deterioration of seeds even if mechanical and fungal damage are absent. Adequate ventilation of orthodox seeds is necessary to avoid rapid respiration and overheating, while recalcitrant seeds must be protected against excessive drying.
Freedom from fungi and insects. For species stored at low temperature and low moisture content, the storage conditions themselves should prevent the development of fungi and insects. It is necessary, however, to avoid collection of crops showing a high incidence of fungal or insect attack and to carry out all operations of collection, transport, processing etc. Attack by fungi and insects is most rapid on the forest floor, so collection from the ground should be carried out as soon after fruit fall as possible. Fungicidal treatment cannot be generally recommended since it can be harmful to seeds Magini ; many fungicides are only effective when dissolved in water and are inappropriate for dry storage.
For seeds which cannot be dried, other measures may be needed. For example seeds of Quercus are fumigated with serafume or other chemicals or heated in warm water for control of weevils Belcher , Olson , while methyl bromide or carbon bisulphide are also commonly used to kill insects Boland et al. Initial viability. Seed lots with high initial viability and germinative capacity have a higher longevity in storage than those with low initial viability. Germination tests, preceded if necessary by appropriate pretreatment to overcome dormancy, should be carried out on a sample of each seed lot before storage, in order to determine how long the seed is likely to retain viability in storage.
Longevity of the viable seeds is correlated with the percentage which germinate in the initial test. Deterioration in initial viability may not be serious if the seeds are to be sown within a few weeks or months, but only good quality seed should be stored for long periods Holmes and Buszewicz , Magini It may be noted that initial viability and germinative capacity are frequently the resultant of the factors described in previous paragraphs seed maturity, mechanical damage, fungal or insect attack.
In common with all other living things, seeds are subject to ageing and, eventually, to death. Nomographs for the effects of temperature and MC on physiological ageing of seeds have been constructed for several agricultural crops Ellis and Roberts Both seed lots would have the identical physiological age, though stored for very different periods of time.
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Similar effects can be expected in orthodox seeds of forest trees. A number of physiological changes in cell tissues may be associated with physiological ageing in seeds. They include 1 Loss of food reserves caused by respiration, e. It is still uncertain to what extent these various effects are the causes or only the symptoms of deterioration, but it has been suggested Villiers that the production of free radicals is the first effect of ageing and that damage to the several systems in the cells is the subsequent result of the release of free radicals.
Whatever the exact mechanism of seed deterioration, there is a consensus that, in orthodox seeds, loss of seed viability is largely governed by the rate of respiration. Any measures which reduce the rate of respiration without otherwise damaging the seed are likely to be effective in extending longevity during storage. These are the control of oxygen, the control of moisture content and the control of temperature.
In recalcitrant seeds the safe minimum levels of oxygen, moisture content and temperature, and hence of respiration, are all considerably higher than those for orthodox seeds but, provided levels are maintained above the safe minima for each species, it appears that longevity can be extended by keeping them as close to the minima as possible in order to avoid an excessively high respiration rate. The most obvious method of reducing the rate of aerobic respiration is to exclude oxygen from the atmosphere surrounding the seeds.
This can be done by replacing oxygen by other gases such as CO 2 or nitrogen, or by using a partial or complete vacuum. The value of excluding oxygen during storage of dry orthodox seeds has also been demonstrated in Pinus radiata Shrestha, Shepherd and Turnbull Best results were obtained with a storage atmosphere of nitrogen, followed by CO 2 , while vacuum and air both gave poorer results. The same ranking was obtained by comparing the speed of germination and the vigour of germinated seedlings measured as dry weight 49 days after sowing.
Although increases in seed longevity of this magnitude have been achieved experimentally, some of the methods are expensive to apply and the effects on seed life are less dramatic than the effects of differences in temperature and humidity Goldbach Exclusion of oxygen will prevent aerobic, but not anaerobic, respiration, whereas reduced MC and temperature will decrease the level of both. While systematic predictions have been made of seed longevity under a range of temperature and MC for several agricultural crops Ellis and Roberts , similar quantitative predictions of the effect of oxygen levels on longevity are lacking.
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One simple method which is recommended is to fill sealed containers as nearly full as possible. If there is only a small amount of air inside the container as compared with the volume occupied by the seeds, oxygen will be consumed and CO 2 produced. Whereas the complete exclusion of oxygen from the storage atmosphere appears beneficial to most dry orthodox seeds, there is evidence that some oxygen is necessary for recalcitrant seeds.
King and Roberts record a general consensus that adequate ventilation i. The relationships of seed moisture content on a wet weight or fresh weight basis to seed MC on a dry weight basis, and of the equilibrium moisture content of seeds to the relative humidity of the surrounding atmosphere, are important in seed processing and are explained on pp. They are equally important in seed storage. In the first case manipulation of RH can effectively change MC of seeds to the optimum for storage, in the second case MC can be maintained at or near that optimum by maintaining a suitable RH in the atmosphere around and between the seeds.
Effect of MC. In orthodox seeds, moisture content is probably the most important single factor in determining seed longevity Holmes and Buszewicz Reduction in MC causes a reduction in respiration and thus slows down ageing of the seed and prolongs viability. Harrington , cited by Barner b , has related MC to various processes within and around the seed as follows:. Prevention of fungal activity is more easily achieved by controlling MC than by controlling temperature.
Oily seeds will usually tolerate drying to a somewhat lower moisture content calculated on the basis of total fresh weight than will non-oily seeds Harrington Betula papyrifera was successfully stored at 0. Methods of drying are described on pp.
Some orthodox forest trees store best at appreciably higher MC. As mentioned on p. For seeds of Abies spp. Species which benefit from storage at higher than average MC also need particular care in the timing and speed of drying. Fluctuation in the moisture content of seed in storage due to open storage without humidity control or to frequent opening and resealing of sealed containers results in deterioration in the germinability of the seeds Wang , Stein et al. In fact a steady MC slightly above the optimum is usually less harmful than one which fluctuates between the optimum and a higher moisture content.
Some cases have been reported in which the usual trend of decreasing seed longevity associated with increasing MC is reversed at or near the moisture content of fully imbibed seeds. If the species in question needs exposure to light in order to germinate, it is possible to store fully imbibed but ungerminated seeds for some time in the dark.
It has been postulated that imbibed seeds can repair damage to cell membranes, enzymes and DNA in the cell nucleus caused by free radicals in a way which is not possible for seeds at lower MC. Prolonged imbibed storage may, however, be difficult in practice, because of the need to maintain constant high moisture for imbibition and adequate oxygen without allowing the seeds to germinate or encouraging the multiplication of fungi and bacteria Roberts Moisture content is also important in recalcitrant seeds, but in this case the critical MC is the minimum to which it is allowable to dry the seeds rather than the maximum content for prolonged storage.
Storage should be carried out at close to the minimum safe MC, since the higher the MC the higher the respiration rate and the more rapid the loss of viability. Higher respiration rates release higher amounts of energy and there is a risk of overheating and death of the seed, unless great care is taken to provide adequate aeration. High MC also increases fungal activity and the spread of rot. Loss of viability in this species may be sudden. Less research has been done on tropical recalcitrant species, but there is some evidence e. On the basis of experiments carried out on Shorea parvifolia and Dipterocarpus humeratus , Maury-Lechon et al.
Although tropical recalcitrant seeds cannot yet be stored for more than short periods, there is a growing body of useful research on the problem. King and Roberts contains a good summary of achievements and possible approaches. Temperature, like moisture content, is negatively correlated with seed longevity; the lower the temperature the lower the rate of respiration and thus the longer the life-span of the seed in storage.
For orthodox seeds, which can be dried to a low moisture content, still greater longevity can be assured by storage at sub-freezing temperatures. Much lower temperatures have been used with success on an experimental basis, e. Choice of storage temperature varies considerably according to species and the period for which the seed is to be stored. The lower the temperature that has to be maintained in a cold store, the higher the cost, and provision of subfreezing temperatures may be unnecessary if seed is to be stored for only a year or two for afforestation projects.
Holmes and Buszewicz noted that, in a number of experiments on conifers, the superiority of sub-freezing temperatures became evident only after prolonged storage over periods of about 5 years or more. Some seeds keep well at room temperature, e. Most species, however, only keep well for longer periods at lower temperatures. Temperature and moisture factors are so interrelated that it is very difficult to separate them. In short, it can be said that the critical moisture content lies at a higher level when storage temperatures are low than when they are intermediate or high, i.
Holmes and Buszewicz It is, however, necessary to avoid any risk of freezing damage caused by ice formation in seeds of high MC. As mentioned in Chapter 6, the equilibrium moisture content of many seeds at a given RH varies with temperature. Species included Pinus as well as several agricultural crops. Change of equilibrium moisture content with change of temperature can be of importance in open storage. In sealed containers the effect is minimal because the final EMC is dominated by the initial MC of the seeds and not the moisture of the enclosed air.
As with moisture content, repeated fluctuations in temperature lead to loss of viability. As far as possible, temperature should be maintained at a uniform level. The effect of temperature on seed longevity of temperate recalcitrant species is similar to that of orthodox species - within certain limits the lower the temperature the longer the period of viability. Some tropical species are killed by temperatures above freezing e. Other species of dipterocarp have a much shorter seed life. Below-freezing temperatures, on the other hand, often kill recalcitrant seeds which need to be stored at a high moisture content Harrington , Wang Light, particularly ultra-violet light, is reported to be harmful to seed Harrington , but very few studies have been made.
Use of opaque metal containers would be preferable to glass jars or bottles for species which are affected by light. But light appears to be much less important than either moisture content or temperature. A number of different storage methods are available, as described below. The main factors affecting choice are the seed characteristics of the species in question, the period for which it is to be stored and the cost. If more than one method is suitable to maintain viability for the required period, the simplest and cheapest will normally be chosen. Seeds can be stored in piles, single layers, sacks or open containers, under shelter against rain, well ventilated and protected against rodents Holmes and Buszewicz , Magini , Stein et al.
Best results are obtained in cool, dry climates. In these conditions several species of Pinus , Eucalyptus Pseudotsuga and Tectona will store satisfactorily for at least six months, while leguminous trees with impermeable seedcoats and naturally low MC, e. Acacia Prosopis , Robinia will retain viability for years Magini , Stein et al. Storage life is further prolonged if cool, but not controlled, temperature conditions can be provided, e.
In forestry it is more common to rely on predrying of the seed to the correct MC, followed by storage in full, sealed containers. Provided that the containers are not opened too frequently and that the sealing is effective, the method will maintain a low MC for many years. It is cheaper than using a humidity-controlled room, especially during periods when only a little seed is in store, and it is not subject to hazards of mechanical breakdown. This method is suitable for a range of species including many Pinus and Eucalyptus species, for which it should maintain viability for one or more years.
This storage treatment is the standard practice for many orthodox species which have periodicity of seeding but which are planted annually in large-scale afforestation projects. Some cool-temperate genera benefit by storage at sub-freezing temperatures, e. Pinus merkusii is an example of a tropical pine which responds well to storage at low temperature and MC. In addition to true seeds, this method is also suitable for certain types of fruits.
This is likely to be equally appropriate for orthodox seeds of forest trees requiring storage for genetic conservation. The quantity of seeds requiring this standard of storage is small in comparison with the quantities used each year for operational afforestation, and the cost per kg of seed is higher. For many countries it would therefore be desirable that forest and agricultural crop genetic resources should share a common long-term storage facility.
Loss of viability in storage, in addition to reducing the number of plants which can be produced by a given seed lot, may result in a shift in the genetic constitution of the seed being stored. This could be particularly important in forest trees which are predominantly outbreeding, variable populations.
Yet they may have valuable traits for adaptation, growth or disease resistance as growing trees, and in any case they contribute to genetic variation in the species which it is the purpose of genetic conservation to preserve. Secondly, it is an accepted fact in agriculture that chromosome damage or change occurs and accumulates in the seed in storage, and that the risk of such heritable gene mutations depends not so much on the age of the seed as on changes in its viability Roberts , Barner b.
The fruit, however, will have a mixture of the two parent's characteristics. Although this may be disheartening for the person trying to preserve that favorite fruit it should be pointed out that many of our current apple cultivars were discovered as chance seedlings. Another reason for growing plants from seed is to produce seedlings onto which you can vegetatively propagate a desired cultivar. Again the resulting seed will be a mixture of the parent's characteristics, and a plant selected because of its growth habit will not come true from seed.
It may be more or less vigorous or more or less susceptible to pests. In either case tree fruit can be grown from seed if handled properly. There are three basic methods that can be used. Both methods require a period of after ripening of the seed. Tree fruit seeds require a period, after the fruit is ripe, before they will germinate and form new plants. During that period the embryo of the seed develops until it is mature. The after ripening is usually accomplished by exposing the seeds to a period of cold. Prepare a garden soil plot in the fall as you would for planting any other type of seeds.
Make a furrow that is no more than 1 to 2 times deeper than the longest dimension of the seed. Cover the seeds with a light cover soil and add 1 to 2 inches of sand over the row. This will prevent crusting of the soil which inhibits germination. Next, place a wire screen over the row. Push the edges of the screen several inches into the soil on all four sides.
This prevents chipmunks and squirrels from digging up the seeds. The following spring carefully watch the seeded area closely for newly germinated seedlings. As they grow, remove the wire screen to prevent bending of the new plants. Remove all adhering fruit portions and allow the seeds to air dry. Then place them in a glass jar to which a loosely fitted lid or cover may be added. Set the seeds aside until mid-January. Mix the seeds in mid-January with either moist but not wet sphagnum peat moss, sand or shredded paper towels. Return the mixture to the jar and replace the lid.
Storing Seeds: How to Preserve Seeds for Years
Place the jar with the seeds in a refrigerator until after the last severe spring frosts have occurred in your area. The seeds should remain in the refrigerator for at least 60 days. In the early spring prepare a seedbed, with furrows as described above, and plant the seeds. Germination may be enhanced by soaking the seeds in water for 12 to 24 hours before planting. Keep the soil moist. Do not add fertilizer at planting. Line the seeds out in trays of moist peat moss or vermiculite.
After they germinate, plant them about 1 inch deep in parallel seed lines about 2 inches apart. After several months in a 40 degree F refrigerator the healthy seeds should germinate and sprout. Transplant them into 4 inch pots with soft tweezers, when they had 2 to 4 true leaves not counting the cotyledons. You could also group the resultant seedlings by their probable chill unit requirements, assuming that those germinating first had lower chill requirements. With all methods, after the seedlings are 6 to 8 inches tall carefully band 1 to 2 tablespoons of urea along each 12 inches of row.
Keep the fertilizer about 2 inches away from the plants.
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