The preservation of seeds after harvest, until they are planted for productive crop growth, is known as seed storage. The seeds must be properly stored for a short or long time to preserve them. Moisture is well managed during seed storage to prevent degradation.
Because seeds can endure moisture loss, they can continue to be viable in a dry condition. When the mother plant reaches physiologic maturity, storage begins there. The seeds are either kept in retail stores, warehouses, trucks, or other locations after harvest. Farmers would occasionally employ farm-saved seeds back in the day, but the emergence of high-yielding types and hybrids, as well as agriculture’s industrialization, made it necessary to establish storage methods for the seeds.
The practice of keeping seeds in storage dates back to ancient times, when it was done using easy and affordable methods like putting seeds in salt or treating red gram with red earth. However, due to the need to preserve a lot of products, the trade of species and variations, and the flow of genes, these methods are no longer appropriate for modern agriculture.
The origins and functions of seed storage
Since people first began to cultivate land in the Middle East 10,000 years ago, seed storage has been a crucial component of civilisation. The archaeological evidence includes clay pots with remnants of stored seeds and holes with stone walls. The Bible’s book of Genesis has one of the first documented accounts of seed storage, in which Joseph gathers food from abundant harvests for storage against an impending famine in Egypt.
The pyramids are built in a fashion that preserves low humidity and constant temperature, two crucial elements in sustaining the viability and vigour of the majority of stored seeds, even if the Bible does not detail the storage facilities. However, reports of living seeds being discovered in the pyramids dating back 3000 years must be treated with suspicion. The sacred lotus (Nelumbo nucifera), whose seeds were discovered on a dry lake bed in Pulantien, China, was the oldest living seed ever discovered. These seeds, which had a radiocarbon age of more than 1000 years, produced seedlings.
The dry Chinese lake bottom offered consistent conditions of relatively low temperature and humidity, just like the pyramids. Additionally, the lotus seed’s tough pericarp acts as a barrier to the movement of water and gases between the seed and its surroundings. This nearly perfect confluence of elements reduces the risk of membrane deterioration due to hydration or oxidation and explains the extraordinary storage life of sacred lotus seeds.
The preservation of food value and viability is one of the main goals of seed storage. Seeds saved for later planting are typically held for no longer than 3 or 4 years, whereas seeds intended for food processing (milling, malting, oil extraction) are typically stored for no more than 2 years. In seed banks, where the facilities are built to retain seed viability for tens or even hundreds of years, seeds are conserved to preserve genetic variety.
Importance of Proper Seed Storage
From harvest until planting, good seed germination and vigour are maintained by seed storage. It’s crucial to obtain enough plant stands in addition to strong, healthy plants. Every seed business should or has a purpose. From the moment the seeds are harvested until they are planted, seed storage is meant to keep the seeds in good physical and physiological condition.
Of course, since there is typically a delay between harvest and planting, seeds must be kept in storage. The seed has to be maintained somewhere throughout this time. Although the primary justification for keeping seed is to shorten the period between harvest and planting, there are additional factors to take into account, particularly when seed storage is prolonged.
In certain cases, seed producers are unable to sell all of their seeds during the subsequent planting season. Unsold seeds are frequently “carried over” into storage for selling during the next planting season. Some types, varieties, and quantities of seed do not transfer particularly well, which causes issues with carryover storage.
To avoid having to generate the seed every season, seeds are also purposefully kept in storage for long periods. This has been proven to be a cost-effective method for seed types for which there is little demand by foundation seed units and others. Some seeds are kept in storage for long periods to increase the proportion and speed of germination by allowing time for a “natural” thawing out of dormancy.
Whatever the precise justifications for seed storage, the goal of maintaining a sufficient capacity for germination and emergence remains the same. Therefore, it is necessary to focus the storage facilities and procedures on achieving this goal.
In its widest meaning, the seed storage period starts when it reaches physiological maturity and ends when the embryonic axis resumes active growth or germination. When seeds achieve their maximum dry weight, they are said to be physiologically and morphologically mature.
The seed is already beginning to dry out or dehydrate at this point. After reaching physiological maturity, dry-down continues until the moisture content of the seed and fruit falls to a point that enables effective and efficient harvest and threshing. Harvest maturity might be applied to this stage.
Between physiological maturity and harvestable maturity, there is often a period, and this phase is the initial part of the storage period. Any postponements in seed harvesting, once they reach harvest maturity, lengthen the initial storage duration, frequently at the expense of seed quality.
From harvest till the start of conditioning is the second part of the storage phase. The same variables that impact the quality of seed during the packed seed portion of the storage period also affect seed in the combine, grain wagon, bulk storage, and drying bins when they are in storage.
The start of conditioning and packaging mark the beginning and end of the third storage period phase, respectively. The packed seed phase, which has previously been stated, makes up the fourth stage of the storage time. The sector for packed seeds comes next, then storage during marketing and distribution, and lastly storage on the field before and during planting.
From a high degree of management from harvest through distribution to considerably less control during the post-maturation-preharvest, distribution-marketing, and on-farm segments, a seedsman has some degree of control over each segment of the seed storage period. The seedsman’s preparations for storage must take into account all of the segments, despite varying degrees of control over the various storage time segments. If the seed’s quality is to be preserved, the things that can be done must be done.
Ensuring the Longevity of Seeds
The amount of time that a seed may survive is known as its lifetime or longevity. A complicated feature is, seed lifespan varies widely between species and even within seed batches from the same species.
From anecdotal “Thumb Rules” to empirically based models, biophysical explanations for why those models sometimes work or fail, and finally the profound realization that seeds are the model of the understudied area of biology when water is so scarce that the cytoplasm solidifies, our scientific understanding of seed longevity has advanced. Temperature and moisture levels in the environment have a critical role in deciding whether an organism will live or die, as well as how long it will exist.
The mechanisms by which these elements trigger cytoplasmic solidification and influence glassy properties. The chemical processes involved in ageing are slowed down but not stopped by cytoplasmic solidification. Protein, lipid, and nucleic acid degradation that doesn’t stop harms cell components and lowers the seed’s metabolic capability, which finally hinders germination.
The technological developments related to seed ageing mechanisms over the past five decades are outlined in this study, including tools to predict seed storage behaviour and non-invasive methods for seed lifespan evaluation. It is claimed that seed physiology, biophysics, biochemistry, and multi-omic technologies are all included in the difficult field of research known as seed storage biology. To increase the effectiveness of seed storage for crops and the preservation of wild species’ biodiversity, concurrent knowledge progress in these fields is required.
To fulfil the Green Revolution’s promises of better agricultural yields or to fend off the growing threat to plant populations brought on by social pressures or the changing environment, the conservation of plant genetic resources is necessary on a worldwide scale. The most effective way to assure the availability of plant genetic resources is to store seeds, and during the past 50 years, the fundamental question of how long seeds can survive has gained relevance in response to demands that have emerged in both the agricultural and conservation sectors.
For more than a century, farmers and the seed industry have struggled to provide a credible estimate of the length of time that seeds would stay viable (also known as lifetime or longevity). Ewart compiled a list of seeds with short, medium, and extended lifespans that were kept in ambient settings in 1908.
Since then, we have gained a better knowledge of the elements that affect seed lifetime, and using controlled settings to extend seed viability has significantly advanced gene banking.
The amount of seed moisture and the storage temperature have a significant impact on the longevity of the seed. According to Harrington’s “Thumb Rules,” the effects of temperature and moisture are independent of one another and add up to a halving of seed life span for every 5 °C rise in seed storage temperature and 1% increase in seed moisture content. The first criterion does not apply at temperatures below zero degrees Celsius or above fifty degrees, according to Harrington.
Empirical data made at temperatures between 5 °C and 50 °C and relative humidity (RH) between 60% and 90% are consistent with the cumulative effects of moisture and temperature that are predicted by models. It is now known that when temperature and moisture availability decrease, the seed undergoes significant physical changes that rely on how moisture and temperature interact.
The commonly used categorization of seed storage behaviour—orthodox, resistant, and intermediate—was developed in 1973 and refined in 1991. It serves as the foundation for understanding why short-lived and desiccation-sensitive seeds do not respond well to normal storage settings.
Because most traditional seeds keep themselves better when they are dried and kept at low temperatures, seed genebank standards (also known as the “conventional method”) were established. These standards provide for storing seeds at a temperature of 20 4 °C and relative humidity of 15 3%.
There is no a priori knowledge to predict seed response to storage for many species of conservation importance, hence techniques have been created to predict seed storage behaviour utilizing environmental signals, seed morphological structure, seed mass, desiccation, and temperature sensitivity.
The phrase “exceptional species” has recently been used to recognize the need for cryo biotechnology methods that genebanks may utilize to preserve species that have a reproductive failure or produce seeds that don’t keep well under circumstances advised by the FAO. Growing expertise in cryobiology and cryo biotechnology offers chances to preserve rare and stubborn species, especially those that are in grave danger.
It has been known for the past 50 years that the external storage environment—temperature, relative humidity, and oxygen—as well as internal seed characteristics—structure and chemical composition—have an impact on how quickly seeds age.
This ageing can be identified through physiological, physicochemical, cytological, molecular, and genetic changes. Recent developments in the knowledge of seed ageing relate to the loss of viability and vigour. Reactive oxygen species (ROS) oxidative damage to lipids, proteins, and nucleic acids are linked to seed ageing during storage.
This knowledge sparked research towards the creation of biochemical indicators that may accurately forecast viability loss and supplement conventional germination testing. Non-destructive techniques, such as seed volatile measurement and seed thermal fingerprinting, have been suggested for predicting seed viability for small seed quantities.
Factors Affecting Seed’s Storage Longevity
1. Seed Kind or Varieties:
The kind and variety of seeds have a big impact on how long they can be stored. Some types, like onions, soybeans, peanuts, etc., have a limited lifespan by nature. Similar kinds, such as Tall fescue and Annual Rye Grass, differ greatly in their capacity to store food, although having very similar appearances. In a similar vein, the genetic makeup of the lines or variations within a kind can also affect storability.
2. Seedling Quality:
The seed lots with healthy, undamaged seeds last longer in storage than the degraded lots. Even seed lots with acceptable germination at the beginning of storage can and can drop fast within a few months, depending on the severity of damage or degree of degradation, E. g. level of weathering damage, mechanical injury, flat, wrinkled, or other damaged seed.
The crucial significance of this is that only top-notch seeds need to be transported. Only the next plating seasons may use the seed of poor quality. The inferior seed must always be discarded.
3. The moisture content
In most of the moisture range, the rate of degradation increases with the moisture content on seed storability, making the quantity of moisture in the seeds likely the most significant factor determining seed viability during storage.
Content of Moisture and Storage For seeds with high germination and high vigour at the beginning of storage, the life of cereal seeds at temperatures not exceeding 90 0 °F has been documented (Harrington and Douglas, 1970).
Additionally, if seeds are stored at moisture levels beyond those listed in the table, losses may occur very quickly owing to heating (18–20% moisture content) or mould development on and inside the seed (12–14% moisture content). Additionally, when the temperature rises, the biological activity of seeds, insects, and moulds increases even more within the usual range. The more negatively impacted seeds are by both extremes of temperature, the more moisture they contain.
It is significant to note that seeds with extremely low moisture contents (below 4%) may potentially suffer harm from acute desiccation.
It is vital to dry seeds to safe moisture contents since a seed’s survival and lifespan are highly dependent on the amount of moisture in the seed. However, the safe moisture level is dependent on the period of storage, the kind of storage structure, the type and variety of seeds, and the type of packaging material employed.
Seed drying up to 10% moisture content seems to be pretty appropriate for cereals stored under normal circumstances for 12 to 18 months. However, depending on the specific variety, drying up to 5 to 8 per cent moisture content may be required for storage in sealed containers.
4. Temperature and Relative Humidity During Storage:
By far, temperature and relative humidity have the greatest impact on how long seeds may be stored. When exposed to a certain quantity of ambient humidity, seeds develop a moisture content that is quite distinct and unique. Equilibrium moisture content refers to this property’s level of moisture for a specific speed and relative humidity, and it tends to rise as the temperature drops and the condition deteriorates.
Since there is no net gain or loss in seed moisture content at equilibrium moisture content, the maintenance of speed moisture content during storage depends on relative humidity and to a lesser extent temperature.
The seed will acquire or lose moisture until an equilibrium is reached with the new environment if it is placed in an environment with a relative humidity that is greater or lower than that with which it is in balance. The relative humidity of the atmosphere inside the containers in sealed storage is determined by the moisture content of the seeds.
It takes time for seeds to reach an equilibrium moisture level. It doesn’t happen right away. The amount of time needed varies depending on the type of seed, the starting moisture content, the typical relative humidity, and the temperature. Seed moisture content varies with variations in relative humidity when stored in open storage. Normal daily variations in relative humidity, however, have no impact on moisture content.
Although it doesn’t seem to be a governing factor, temperature has a significant effect on the life of seeds. The biological activity of seeds, insects, and moulds increases when the temperature rises within the typical range. The more moisture the seeds have, the more temperature has a detrimental effect on them. Therefore, lowering temperature and seed moisture levels is a useful strategy for preserving seed quality while it is in storage.
Even when relative humidity is relatively high, low temperatures are quite helpful in maintaining seed quality. Relative humidity for seed storage in the cold should not be more than 60%.
5. Provability
The viability of seeds can be impacted by a variety of variables that operate before and during harvest. Therefore, it is surprising that seed samples from various sources may exhibit varying viability behaviours. Due to the significant variation across samples from various sources, it is frequently difficult to identify and evaluate the origins of these discrepancies, or even to determine how significant they are.
However, the seed starts to exist before it is harvested. Furthermore, it is only reasonable to assume that seeds gathered under various pre-harvest conditions will have undergone varying degrees of degradation by the time they are harvested.
6. How Variable Environmental Conditions Affect Viability:
Despite some claims to the contrary, there is currently no a priori reason to believe that variations in temperature or moisture content would be detrimental in and of themselves, with the possible exception of extremely quick changes in seed moisture content.
It is necessary to do more thorough research on the impact of changing environmental circumstances.
7. Extreme Storage Conditions Have a Special Effect on Viability.
According to studies, germination will result in a loss of viability when seeds are very moist, and if seeds are subjected to extreme desiccation, the period of viability may be less than one year in cereals under three sets of extreme storage conditions of temperature and moisture contents, say about 30%.
8. Pressure of oxygen
Increases in oxygen pressure tend to shorten the time of viability, according to recent studies on the impact of a gaseous atmosphere on seed viability. According to little research on the use of antioxidants, heat damage to kidney bean embryos was lessened in environments with lower oxygen pressures, and the administration of cysteine partially reversed the damage.
Starch phosphate is particularly successful in extending the viability of both spp., while alpha-tocopherol showed some positive effects on onion seeds, according to research on onion and okra seeds treated with either substance.
The activity of Organisms Related to Seeds in Storage is Affected by Storage Conditions:
When seeds are kept in storage, six major types of organisms are involved:
- Bacteria
- Fungi
- Mites
- Insects
- Rodents and
- Birds
All of these organisms have the potential to cause harm, including the loss of vigour or viability or, in the case of rodents, the total loss of seed.
fungus and bacteria. The inter-seed atmosphere’s relative humidity is a crucial factor in the management of seed microflora. The number of fungi in a seed frequently exhibits an exponential connection with relative humidity, with all storage fungi entirely inactive below 62 per cent relative humidity and very little activity from roughly 75 per cent relative humidity upwards.
The development of the storage bacteria requires at least 90% relative humidity, therefore they only become relevant when fungi are present.
Certain organisms may develop at temperatures as high as 80 0 C, which is the influence of temperature on the growth of the micro-flora. Deep freezing is the only viable way to regulate micro-flora activity by temperature alone since high temperatures quickly reduce seed viability. There are currently no effective chemical controls for these organisms in storage.
No insect activity is seen at seed moisture values below 8%, but if the grain is infected, increasing activity may typically be anticipated up to roughly 15% moisture content. The ideal temperature range for the more significant storage insects is between 28 and 38 0 C. The term “cold” refers to temperatures between 17 and 22 0 C.\
Although altering the seed environment is typically preferred for controlling insect and mite activity, it is feasible to manage these organisms chemically, i.e. by the use of fumigants and contact pesticides. One issue with chemical management is that some of the chemicals might be hazardous to handle and hurt seed viability or vigour.
However, fumigants such as methyl bromide, hydrogen cyanide, phosphine, ethylene dichloride and carbon tetrachloride in a 1:3 ratio, carbon disulphide, and naphthalene have been employed effectively. DDT, lindane, and malathion are a few of the contact insecticides that are utilized in seed storage.
Birds and rodents. If there are even little gaps at the edges or between the roof tiles, birds can be a persistent source of seed loss. Any apertures that are required for ventilation should be screened or sealed. More significant issues arise from rats and other animals. Rodents might cause the seed to completely disappear.
Construction of the shop with the floor 90 cm above ground level at the entrances, a 15 cm lip around the building at the 90 cm level of the floor, and the provision of a detachable deck at the entry for use only when the seed is being loaded or unloaded are all examples of rodent control methods.
9. Additional factors
In addition to the factors already mentioned, other factors that impact seed storage life include direct sunlight exposure, the frequency and kind of fumigation, the results of seed treatment, etc.
- Storage in Transit, at the user’s farm and the retailer’s shop. It is of little value to build superb warehouses if the seeds are subsequently damaged by incorrect storage while in transportation, at the retail location, or on the user’s field. Therefore, it’s equally important to take adequate storage measures at each of these locations.
The Science Behind Seed Preservation
A long-standing agricultural practice that includes a wide range of methods is seed storage. Traditional seed storage techniques and commercial seed banks both rely on regulated environmental conditions to keep seeds viable for longer periods. The most popular technique of seed storage in the modern agriculture sector is seed banks.
When we talk about seed banks, we usually mean vaults filled with seeds that have been stored from a variety of plant species, from economically essential crops to critically endangered ecologically significant plants. Natural catastrophes, as well as other possible risks like radiation or explosives, are not allowed to enter these vaults. These institutions serve a variety of purposes but primarily operate as seed banks to protect the genetic diversity of plant species.
To ensure that seeds can develop when needed in the future, conditions in a seed bank are typically low in humidity and temperature, with temperatures about –20°C. There are more than 1,000 such seed bank facilities worldwide, with the Millennium Seed Bank in Sussex, United Kingdom, housing the biggest collection—about 40,000 different plant species.
Throughout human history, seed banks have been used; there have even been accounts of seeds being discovered in Egyptian pyramids and palaces. Although the longest seed storage now available lasts 150 years in vaults, the exact lifespan of seed storage itself is yet unknown.
The health and reuse of seeds stored in seed banks have only been studied in food science, which has discovered various obstacles limiting the potential effectiveness and usefulness of seed banks until the first vaults reach 1,000 years old or more.
The second part of this article can be read HERE
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