Seed Biology: Advances and Applications
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This book contains edited and revised papers from the 6th International Workshop on Seeds held in Mexico in January and describes the status of seed research and technology. Convert currency. Add to Basket. Condition: New. New Book. Shipped from UK. Established seller since Seller Inventory CA More information about this seller Contact this seller.
Condition: new. Black, etc. Bradford, J. Vazquez-Ramos, Substantial progress has been made in seed science during the past few years, emphasizing the important role seed biology plays in advancing plant biotechnology, agriculture and plant resource management and conservation. Seller Inventory B Book Description Stylus Pub Llc, Condition: Brand New. In Stock. Language: English. Brand new Book. This book discusses the biology of seeds.
Seller Inventory BTE Seller Inventory BD First - may be Reissue. This, and the fact that populations of wild species are unlikely to be found growing in isolation across a large area of land, means that it may be difficult to collect a large quantity of seeds, and what is collected may have variable maturity; this can cause problems during processing and may limit the number of seeds available for storage, testing, and distribution.
Summary of some of the differences between cultivated and wild species that influence our ability to store, manage, and use accessions of the latter and some of the potential future foci for further research. It is expected that seed bank collections of wild species will play an increasingly important role in habitat restoration and reintroduction of species Merritt and Dixon, Hence, it is vital that collections of wild species are managed effectively and that sufficient viable seeds are available for use or for producing larger volumes of seeds.
This review will consider the current knowledge that is available to guide the management and use of wild species collections in seed banks. Seed-bearing species may, in most cases, be grouped into one of the following three categories of seed storage behaviour: recalcitrant desiccation intolerant ; intermediate partly desiccation tolerant and sensitive to low temperature ; or orthodox desiccation tolerant.
Non-orthodox seeds cannot be stored successfully long-term using conventional genebank protocols drying and storage at low temperatures. Fortunately, most flowering plant species, including most major and minor food and agricultural crops, do produce seeds that are orthodox. Liu, personal communication.
The procedure for the germination test must overcome any dormancy in the seeds e. Wood et al. For example, dry seeds of some species can be vulnerable to imbibition injury and must be rehydrated gently before exposure to liquid water Bochicchio et al. Browne spp. If it is not possible to carry out the necessary experiments to determine seed storage behaviour, it may be predicted according to taxonomy, origin, and other seed traits.
Although some plant families or genera have representatives showing each category of seed storage behaviour, others may comprise species showing only orthodox or recalcitrant behaviour Royal Botanic Gardens Kew, Non-pioneer, evergreen rain forest tree species have the highest frequency of recalcitrant seed storage behaviour; the frequency declines as the habitat of origin becomes drier Tweddle et al.
Recalcitrant seeds are also likely to be dispersed during the wet season, at higher moisture contents than orthodox seeds, and to germinate readily because there is little or no slowing down of metabolism and development of dormancy common in orthodox seeds; they are also likely to be relatively large and have relatively thin outer tissues Tweddle et al.
Daws et al. Seed storage behaviour continues to be determined experimentally for diverse species e. Xia et al. For the time being, while it may not be possible to make accurate measurements of these traits in the field, it should nonetheless be possible to identify species that could potentially show non-orthodox seed storage behaviour, for which making a large collection for conventional seed bank storage might be a waste of time and resources, without first carrying out tests to check for desiccation sensitivity.
The subsequent sections of this review focus on orthodox seeds, because it is these seeds which may be stored in conventional seed banks. There have been numerous studies on the development of seeds of crop species to identify the optimal time to harvest for maximal quality e. In contrast, only a few studies have considered the development of seed quality for non-cultivated species Hay and Probert, ; Hay, ; Ali et al. The general pattern of seed development in terms of changes in seed fresh and dry mass, ability to germinate before and after rapid drying, and longevity is shown in Figure 1.
Seeds of most orthodox species acquire the ability to withstand drying after they have acquired the ability to germinate when fresh i. The cessation of the accumulation of dry weight is caused by the termination of the vascular connection between the seed and the maternal plant; the amount of water in the seed also starts to decline after this time, as the seed starts to equilibrate to the ambient conditions. During this desiccation phase, seed quality, in particular with respect to longevity in air-dry storage, continues to increase Figure 1.
Seed Biology : Advances and Applications
In the case of non-cultivated species with dry, dehiscent fruits, the seeds are likely to be dispersed at the point when equilibrium with the microclimate is reached, and it is recommended that this would be the optimal time to harvest for maximal subsequent longevity in seed bank storage Hay and Probert, ; Hay and Smith, Determining the equilibrium relative humidity of a sample of seeds will confirm whether or not seeds have equilibrated with ambient conditions Hay and Probert, As well as looking for signs that seed dispersal has or is about to commence within the target population, there may be other indicators of relative maturity, including changes in fruit or seed colour Hay and Smith, ; Hay et al.
Schematic diagram showing the pattern of seed development for orthodox seeds of foxglove Digitalis purpurea L. Mass maturity is defined as the point when maximal dry weight is reached Ellis and Pieta Filho, The dashed and continuous parts of the arrows indicate the time when the trait the ability to germinate before or after drying, and longevity is increasing and stable, respectively. Unfortunately, unless the species being collected is serotinous or otherwise resistant to shattering, the fact that seeds are likely to be readily dispersed means that they are often collected before they are fully ripe.
Furthermore, given the variability in flowering time for many wild species, both within and among individual plants in a population, it is inevitable that a seed collection will contain a significant proportion of seeds that are less mature. The most immature seeds might not survive the enforced, post-harvest seed drying Figure 1 and, while it may be possible to remove under-sized potentially desiccation-intolerant seeds during seed cleaning, this is not ideal if it is difficult to collect a large number of seeds, and the overall quality of the seed lot will be compromised.
Seeds of some species may even need to be kept fully hydrated post-harvest to allow maturation to proceed. Seeds of Anemone nemorosa L.
Likewise, only a proportion of the seeds of Narcissus pseudonarcissus L. Post-dispersal acquisition of desiccation tolerance may occur in other species that occur in cool, damp habitats and whose seeds have under-developed embryos at the time of seed dispersal. Clearly, this is an area that needs further study if accessions with high viability and good storage potential are to be placed into long-term seed bank storage.
The procedures recommended for processing seeds prior to banking, i.
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However, cleaning and sorting seeds, and other activities, may still be predominantly manual operations in many seed banks. Part of the reason for this is that seed banks are often processing relatively small quantities of each accession, and accessions may be highly diverse, reducing opportunities for automation. This is particularly true of wild species seed banks, where seed size and morphology are likely to vary considerably from one accession to the next.
To some extent, commercial seed companies and seed bank managers have similar goals; that is, to maximize the physical purity, health, and physiological quality of their seeds. For the commercial seed companies, this is because high-quality seeds seeds with high, fast, and uniform germination have greater monetary value, whereas for seed bank managers the purpose is to maintain maximal genetic diversity, and the potential value of an accession is unknown.
Increasingly sophisticated seed-sorting equipment is being developed, involving sorting of individual seeds based on image analysis of external traits size, aspect ratio, colour, etc. However, with any automated sorted technology, the risk of introducing genetic drift must be evaluated. For example, would sorting based on seed size result in the loss of alleles related to seed size? Hence, most seed banks will typically place incoming seeds into a chamber or drying room set within these limits of relative humidity and temperature.
As discussed in the previous section, immature seeds may be better placed in conditions that simulate those that the seeds would experience in situ before final equilibration prior to packing for long-term storage.
Desiccants such as silica gel, calcium chloride, charcoal, and zeolite beads may also be used for drying seeds to low moisture contents Probert, ; Rao et al. Drying without shade is possible, but care must be taken to avoid over-heating, which might cause, for example, cracking Probert, Requests for seed bank samples of wild species, especially of non-CWR species, are likely to be less frequent than those for crop and CWR species.
For example, the T. In the same year, the MSB distributed only samples. Such figures emphasize why it is useful to have samples of crop accessions in both medium-term storage the active collection, with the bulk sample of seeds that will be used for distribution and long-term storage the base collection, holding a smaller quantity of seeds of each accession , with all accessions present in both, while long-term storage conditions alone, as used by the MSB, might be sufficient and most appropriate for wild species.
Crop genebanks are likely to store much smaller quantities of CWR accessions than they do of cultivated accessions. This may be due to lower demand but also because it can be difficult to grow wild species, and seed production rates may be very low. With increase in demand for samples of wild species, it may be necessary to have larger quantities available.
These sorts of quantities are unlikely to be placed into long-term seed bank storage conditions; if multiplication is demand driven, short-term storage following multiplication, in conditions that will maintain viability at adequate levels for a few years, may suffice. Another reason why it makes sense to place wild species accessions into long-term storage conditions alone is that the longevity of the seeds in storage is likely to be unknown. The rate of decline in the viability of seeds has been statistically modelled using the Ellis and Roberts a viability equations for fewer than species, most of which are crops Royal Botanic Gardens Kew, , and most publications containing genebank retest data the results of germination tests carried out to monitor viability have likewise focused on accessions of cultivated material e.
Walters et al. Storage experiments, placing samples of seeds in conditions of relatively high moisture and temperature, and monitoring their viability, have shown that relative seed longevity can vary enormously across diverse taxa Probert et al. Seeds from species within certain plant families or genera appear to be typically short or long lived, and seeds from species originating in cool, wet environments are likely to have shorter lifespans than those from warm, dry environments Figure 2 ; Probert et al.
Mondoni et al. Seed lots of species with the shortest-lived seeds may survive only a year or two at best, even in conventional long-term storage conditions Ali et al. Cryopreservation may be the only recourse to ensure the effective ex situ seed conservation of such species Li and Pritchard, ; FAO, Map of the world showing the predicted relative longevity of endospermic seeds depending on the climate at the origin of the seed lot and based on the relationships published by Probert et al. The general pattern would be the same for non-endospermic seeds, although their longevity is expected to be greater.
Relative seed longevity ranking of species is expected to be similar in seed bank storage conditions, i. This map was created in May by A. Monitoring the viability of seeds during storage, by removal of a sample for germination testing, is an essential aspect of effective management of seed bank collections. Incorporating variable retest intervals into seed bank management software is, of course, possible; the difficulty is in deciding on the method behind setting retest intervals, particularly given that the parameters of the Ellis and Roberts a viability equations have been determined for only a small number of wild plant species.
In addition, even if species constants are known and stable, the longevity of a particular seed lot will depend on the initial quality of the seeds when first placed into storage Probert et al.
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Crawford et al. They speculated that the relatively rapid loss of viability apparent for a few seed lots was accession specific, because in some cases, other accessions of the same species did not show a significant decline. Likewise, Godefroid et al. Thus, it seems that for the management of wild species accessions, caution should be urged and regular monitoring carried out until such time that there is assurance that viability is being maintained or until there are sufficient data to predict when viability will reach the critical level when regeneration should be performed.
A streamlined version of the comparative longevity protocol, designed to screen for short-lived species, has been developed at the MSB. This test uses seeds rather than , and seed viability is monitored at only four intervals during controlled ageing. Probert et al. Significantly different estimates of longevity were obtained for one of the other seed lots; three did not show a significant decline in germination in either test; and for two seed lots, there were too few data to determine longevity parameters; however, both methods would have identified the seed lot to have been short lived.
Plans are now in place to introduce the streamlined test for routine screening of putative short-lived species collected for long-term conservation at the MSB.
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Efficient viability monitoring through a germination test may still be hampered by a lack of knowledge of dormancy-breaking and germination requirements see following section. Godefroid et al. However, one of the problems associated with germination tests on wild plant species is that incubation periods can extend to many weeks or months. Consequently, there is a risk that some seeds might die during the test, especially if germination conditions are not optimal. One way around this problem is to perform cut tests on seeds that have been imbibed for a few days.
Alternatively, a tetrazolium test, in which viable seed tissues become stained a dark red, may also be used to verify viability where germination results are poor ISTA, Tetrazolium testing is routinely used at the MSB Terry et al. Seed vigour tests are very important to the seed industry; seed traders need to know the quality of the product the seed lots being exchanged. The vigour of a seed lot is a trait which encompasses the likelihood and rate at which a seed will germinate and whether the resulting seedling will develop into a healthy plant. Seed vigour tests essentially measure the extent of seed ageing that has occurred, although their precise interpretation in terms of how they translate into results in the field may vary among species, varieties, or variety groups including production methodology, e.
Traditional measures of seed vigour are calculated from the results of a seed germination test and essentially measure the speed of germination, because the speed will slow down as seeds age. These germination parameters include single counts of the proportion of seeds that have germinated after a set period of time in the germination test and expressed as mean germination time MGT; Ellis and Roberts, b or germination index GI; Maguire, Precise calculation of these parameters requires accurate and regular observation, which has led to the development of automated systems to follow the progress of germination in a sample of seeds based on image capture and analysis Matthews et al.
Furthermore, while most seed banks normally record only the percentage germination result, an automated system would enable the accurate and fast determination of a measure of the speed of germination; this could be used as an indicator of seed ageing before loss of viability is apparent Powell and Matthews, Over recent years, advances have been made in understanding the seed ageing process, i. Much of the damage that accumulates in seeds during storage is attributed to oxidation by reactive oxygen species Hendry, ; Bailly, ; Kranner et al.
Ageing processes are slowed in seed bank storage conditions, because the seeds enter a glassy state, and variation in seed longevity between species or seed lots may be due to the properties of that glassy state Walters et al. This area of research may lead to a biochemical marker of viability loss that could be used as an alternative to more time-consuming germination tests.
Like a germination test, however, such a marker may still be destructive. Alternatively, it has been found that seeds can produce volatile compounds during storage e. Zhang et al. Issues regarding our ability to use wild species accessions see following section also apply to our ability to regenerate material for seed bank storage. Perhaps of particular concern, if a species produces seeds that are short lived in storage, is how many cycles of regeneration are acceptable and how to ensure that allelic variation is maintained such that viable living populations could be established if needed in the future.
One of the major impediments to the potential use of wild species germplasm for species reintroduction or habitat restoration as well as causing difficulties for viability testing is lack of knowledge of how to break dormancy and germinate the seed. There is, however, a huge body of literature that can be searched for guidance, if not for the species of interest, then for closely related taxa.
Some of this literature has already been compiled Baskin and Baskin, ; Royal Botanic Gardens Kew, , and seed banks may also publish their own germination data e. Wood, This approach has been successful in overcoming dormancy for a wide range of species e. Karlsson et al. There have been numerous reports linking germination requirements and seed dormancy to local climate. For example, Mott found that the optimal temperatures for germination varied in species adapted to grow during either winter or summer rains in Western Australia.
Germination and emergence phenology is also finely tuned to local climate in the temperate woodland geophyte Anemone nemorosa. In this species, embryo development and germination occurred earlier and at lower temperatures in seeds from a mountain population compared with seeds from lowland populations Mondoni et al. In some cases, germination linked to habitat appears to be under genetic control Meyer and Kitchen, ; Meyer et al. Dormancy is likely to be lost during storage, and the conditions required for germination in particular, temperature become less specific Probert, , although the rate of loss of dormancy is likely to be slower in seed bank storage than it would be in ambient conditions Roberts, As well as loss of dormancy during seed bank storage, induction of dormancy can also occur e.
Technologies that are already routine, in particular in the horticultural industry, may improve success rates. For example, seed priming is often used as an invigoration treatment to ensure rapid establishment Parera and Cantliffe, and could help to ensure that seeds that are sown in situ are able to germinate and establish, particularly if the seeds have already aged during storage Powell et al. This aspect of conservation science, understanding how to produce seedlings from wild species seed bank accessions in quantities sufficient to create viable populations with high genetic diversity, will no doubt expand in the coming years, not least if seed banks are to play a role in restoration and species reintroduction.
Increasing focus may also be directed to how accessions are evaluated for potential use beyond restoration and species reintroduction. Nonetheless, seed banks that are routinely storing seeds of wild species have, by necessity, devised protocols that are effective and practical e.
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Manger et al. Ali et al. Seed conservation research will no doubt continue on a variety of topics Table 1 as seeds of more wild species are collected and stored in seed banks, and as more issues come to light, which is unavoidable given the diversity being considered. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign In. Advanced Search.