Keywords

19.1 Introduction

The typical life cycle of flowering plants involves several distinct developmental stages, beginning from a seed that undergoes the process of germination to form an established plant that then progresses to a reproductive stage, in which specialised organs for reproduction are produced, ultimately enabling new seed production. Given that plants have adapted to their native environments, the time taken between fertilisation and germination of the mature seed can vary greatly between species (Ma et al. 2006). There is an ample evidence that poor crop stand establishment is a widespread constraint of crop production in developing countries, particularly in the marginal environments farmed by poor people. Clearly, anything that can be done to increase the proportion of seeds that emerge, and the rate at which they do so, will have a large impact on farmers’ livelihoods.

Every farmer is sensitive to the need for rapid, uniform seedling emergence because it is the foundation on which stand establishment is based and potential yield is determined. Therefore, fundamental knowledge about mechanism underlying seed development, germinability, dormancy and storability is required to improve the performance of seed. Production of high-quality seeds is fundamental to the success of agriculture since crop production relies heavily on high-quality planting seeds. Quality of seed lot is determined by its physical and genetic purity level. The impurity of the pollen source and the mixture of the parental seeds or other cultivar seeds with the hybrids will also lower the genetic purity of the produced hybrids. Low-purity seed would cause big loss for the seed company from the planters’ claim. Therefore, it is of critical importance to evaluate the genetic purity in seed production and trade (Garg et al. 2006). For years the method used to check hybrid seed purity has been the grow-out test. This consists of growing a representative sample of the F1 seed and later classifying it using descriptors of differences as true hybrid seed or off-types. This method is time consuming, space demanding and often does not allow the unequivocal identification of genotypes.

To make the best use of recently evolved varieties for enhanced seed yield, a systematic but effective package of practices are very much needed. Ambient environments in tropical and subtropical regions are generally not good for seed storage, and therefore the maintenance of viability during storage is a great problem. Storing seed at low moisture content in moisture-impervious containers under ambient condition would benefit countries like India where the cost of low-temperature storage is prohibitive. Horticultural crop seeds are known to be sensitive to temperature during drying. The storability of primed, pelleted and coated seeds is also important as the seeds after treatment need to be stored for considerable period as in the case of normal seeds. Hence, storage studies are required to identify problems involved in storage of such seeds and to identify suitable techniques for safe storage.

The success of seed germination and the establishment of a normal seedling are determining features for the propagation of plant species, which are of both economic and ecological importance. Because of its high vulnerability to injury, disease and water/environmental stress, germination is considered to be the most critical phase in the plant life cycle. Seed quality enhancement technologies have expanded over the last 10 years due to the vegetable industry’s demands for strong and uniform stand establishment. Precision seeding reduces seed costs per acre, and seed enhancement increases production flexibility and harvest pack-out.

Among the seed enhancement techniques, the technique of seed priming has gained popularity since ages due to its beneficial effects like enhancement in seed germination, advancement of germination, pest and disease resistance, better crop stand establishment and stable yields even under adverse conditions. Seed pelleting and coating is a new technology in India. In Western countries, high-value hybrid vegetable seeds are invariably either coated or pelleted and sold. Most of the coating/pelleting materials are patented and costly too. Hence, it is essential to identify suitable indigenous pelleting/coating materials and to develop protocol for pelleting and coating along with nutrients and growth regulators to enhance the seed quality.

Plant varieties developed within a country are invaluable national resources. Farmers contribute in conserving, improving and making available plant genetic resources for developing new plant varieties. It is therefore necessary to protect plant varieties as also the rights of farmers and plant breeders to stimulate investment in research and development related to new plant varieties. This makes high-quality seeds and plant material available to farmers and gives a general boost to the growth and development of agriculture in the country. Putting in place an effective system of protection of plant varieties and rights of farmers and plant breeders is also incumbent in India in view of its ratification of the Agreement on Trade-Related Aspects of Intellectual Property Rights (TRIPS) under the World Trade Organization (WTO).

Under the Seed Act, 1966 of India, labelling is compulsory and certification is voluntary for the seeds sold in the market. Therefore, the Government of India has prescribed standards so that seeds sold conform to the minimum limits of physical purity, genetic purity and germination, maximum limit of moisture content and status of seed health. These seed quality parameters known as ‘seed standards’ have been notified for various crops, viz. cereals, millets, pulses, vegetables, etc.

Seed-testing rules are regularly updated by ISTA (International Seed Testing Association, Switzerland) or AOSA (Association of Official Seed Analyst, USA) on the basis of research work done globally and incorporated in ISTA/AOSA Rules for seed testing. The International Rules for Seed Testing (International Seed Testing Association, Switzerland) contain prescription for all kinds of seed-testing activities of a large number of species cultivated all over the world, and it forms the basic and essential reference book for seed testing and seed trade. The changes in orientation of production and other ancillary changes have affected the seed industry as a whole, creating a new global industry, which is guided by large multinational companies.

Progress in biotechnological research during the last two decades has opened up unprecedented opportunities in many areas of basic and applied biological research. Plant tissue culture, which is an important component of plant biotechnology, presents new strategies for the improvement of cereals, legumes, forest trees, plantation crops and ornamental plants. Nowadays, artificial seed technology is one of the most important tools to breeders and scientists of plant tissue culture. It has offered powerful advantages for large-scale mass propagation of elite species.

19.2 Seed Development and Maturation

Seed is defined as a fertilised, matured ovule consisting of an embryonic plant together with a store of food, all surrounded by a protective coat. The pattern of seed formation, development and maturation in plants was well described (Bewley and Black 1994; Black et al. 2006; Copeland and McDonald 2001; Hartmann et al. 2002), and the readers can refer to these for more information (see also the Chap. 18 in this volume). The quality of seed depends on various factors. Seed maturation in relation to dormancy induction and release was studied through ABA biosynthesis pathway, and genes associated with it, viz. ABA1, the 9-cisepoxycarotenoid dioxygenase, ABA2/GIN1, etc., were identified.

19.3 Seed Dormancy

A dormant seed does not have the capacity to germinate in a specified period of time under any combination of normal physical environmental factors that are otherwise favourable for its germination, i.e. after the seed becomes nondormant. A completely nondormant seed has the capacity to germinate over the widest range of normal physical environmental factors possible for the genotype. Many reviews on seed dormancy and germination published (Finch-Savage and Leubner-Metzger 2006; Hilhorst and Toorop 1997) clearly illustrate why dormancy for some period is important in some crops and ways and means of breaking the same.

19.3.1 Factors Causing Seed Dormancy

A wide range of factors alter seed dormancy, e.g. temperature, light, nitrate salts or naturally occurring chemical signals (ABA and four other terpenes) and leachate from litter that covers the seeds in their habitat.

19.3.2 Primary Versus Secondary Seed Dormancy

Seeds that are released from the plant in a dormant state are said to exhibit primary dormancy. Seeds that are released from the plant in a nondormant state but which become dormant if the conditions for germination are unfavourable exhibit secondary dormancy.

19.3.3 Classification of Seed Dormancy

Seeds with primary dormancy can display exogenous (physical), endogenous (physiological and morphophysiological) or combinational dormancy (physical and physiological).

19.3.3.1 Exogenous Dormancy and Removing the Dormancy

The major type of exogenous dormancy is called physical dormancy and these are often called hard seeds. Physical dormancy is caused by the outer seed coverings preventing the seed from taking up water. In nature, physical dormancy is most often satisfied by exposing the seed to high-temperature conditions. Since this can take many years, scarification is followed alternatively. The three most common ways to scarify seeds include hot water, acid or scratching the seed surface.

Hot-water treatment can be accomplished by placing seeds in water that has just begun to boil. Remove the boiling water container from the heat source and allow the seeds to soak for 1–10 min depending on the seed type. Too long exposure to the hot water can kill the seed. This works for many seeds with physical dormancy, but usually only a small percentage of seeds become able to absorb water.

Acid treatment involves soaking the seeds in concentrated sulphuric acid for various durations, and in most cases it needs to be standardised depending on the thickness of seed coat, e.g. Malvaceae and Leguminosae. Scratching the seed surface with a small file is the recommended method for scarifying small batches of seeds. Scratching is also done by rubbing against rough surface or by other means that removes the upper layer, e.g. bitter gourd. This allows water to penetrate the seed. In clipping method, a portion of the seed is cut at distal end without damaging the embryo so as to facilitate the entry of water into the seed, e.g. Bixa spp. and Terminalia spp.

19.3.3.2 Endogenous Dormancy

Physiological and morphophysiological are the two major types of endogenous dormancy. Morphological dormancy is a third type of endogenous dormancy, but it is most often seen in herbaceous plants.

Seeds with physiological dormancy require a period of moist chilling to satisfy dormancy. A moist, chilling period is called stratification. In nature, physiological dormancy is satisfied by having the seeds in moist soil over the winter. The same conditions can be simulated by keeping the seeds in a plastic bag containing a moist substrate (sand or vermiculite) in the refrigerator for several months. The optimum temperature for stratification is between 1 and 5 °C (35 and 50 °F).

Seeds with morphophysiological dormancy have an embryo that is less than one-third the size of the seed. In most cases, the seeds require a period of moist, warm stratification to allow the embryo to continue development. However, once the embryo completes development, it still has physiological dormancy that requires a period of moist, chilling stratification. In nature, seeds with morphophysiological dormancy can take several years to germinate because they need to be exposed to summer and winter conditions. To get quicker germination, these seeds can be placed moist in a warm place (about 21 °C, 75 °F) for several months before being moved to the cool temperature for several months more.

19.3.3.3 Combinational Dormancy

Combinational dormancy occurs in seeds that have both exogenous (physical) and endogenous (physiological) dormancy. This is not a common form of dormancy, but eastern redbud (Cercis canadensis) is a good example of a plant with combinational dormancy. In this case, the physical dormancy must be satisfied before the physiological dormancy can be relieved. These seeds are first scarified (by scratching the seed coat with a file) to allow seeds to absorb water. This is followed by moist, chilling stratification.

19.3.3.4 Embryo Dormancy

A dormant embryo is characterised by a high ABA/GA ratio, high ABA sensitivity and low GA sensitivity. Embryo dormancy release involves remodelling of hormone biosynthesis and degradation towards a low ABA/GA ratio, a decrease in ABA sensitivity and an increase in GA sensitivity. Thus, ABA dominates the embryo dormancy programme and GA the embryo germination programme. A nondormant embryo is characterised by increased growth potential, the ability for cell extension growth and the ability to induce the release of coat dormancy.

19.3.3.5 Endosperm Dormancy

Endosperm weakening can be either part of the coat dormancy release or part of the germination programme. Since the endosperm is in most cases a living tissue, it can actively participate in regulating embryo constraint by influencing both the ABA/GA ratio and sensitivity to these hormones. GA acts by increasing the embryo growth potential and by promoting endosperm weakening which is achieved through ABA-independent and ABA-inhibited mechanisms (http://www.seedbiology.de/dormancy.asp).

19.4 Seed Germination

To the seed analyst, germination is ‘the emergence and development from the seed embryo of those essential structures which, for the kind of seed in question, are indicative of the ability to produce a normal plant under favourable conditions’. Based on the fate of the cotyledons, two kinds of seed germination occur. When cotyledons remain below soil surface due to rapid elongation of epicotyl, then it is called as hypogeal germination, for example, majority of monocotyledons; some trees like mango, coconut and areca nut; and some large-seeded legumes. When cotyledons pushed above soil surface due to rapid elongation of hypocotyls, then it is called as epigeal germination mostly in horticultural and woody plant species, e.g. cotton, cucumber, guar, gourds, tamarind, castor, sunflower and groundnut.

19.4.1 Requirements for Germination

Water

Water is a basic requirement for germination. In their resting state, seeds are characteristically low in moisture and relatively inactive metabolically. Once seeds absorb water, activation of enzyme occurs resulting in breakdown, translocation and utilisation of reserve material by the growing tissues.

Gases

Air is composed of about 20 % oxygen, 0.03 % carbon dioxide and about 80 % nitrogen gas. If one provides different proportions of each of these gases under experimental conditions, it soon becomes clear that oxygen is required for germination of most species. Carbon dioxide concentrations higher than 0.03 % retard germination, while nitrogen gas has no influence.

Temperature

Seed germination is a complex process involving many individual reactions and phases, each of which is affected by temperature. The effect on germination can be expressed in terms of cardinal temperature: that is, minimum, optimum and maximum temperatures at which germination will occur.

19.5 Seed Testing

Seed testing is done to determine the standards of a seed lot, viz. physical purity, moisture, germination and ODV, and thereby enable the farming community to get quality seeds. The seed-testing laboratory is the hub of seed quality control. Seed-testing services are required from time to time to gain information regarding planting value of seed lots.

19.5.1 Objectives and Importance of Seed Testing

Seed testing is required to achieve the following objectives for minimising the risks of planting low-quality seeds:

  • To determine their quality, that is, their suitability for planting

  • To determine the need for drying and processing and specific procedures that should be used

  • To determine if seed meets established quality standards or labelling specifications

  • To establish quality and provide a basis for price and consumer discrimination among lots in the market. The primary aim of the seed testing is to obtain accurate and reproducible results regarding the quality status of the seed samples submitted to the seed-testing laboratories.

19.5.2 Role of Seed-Testing Laboratories

Seed-testing laboratories are essential organisations in seed certification and seed quality control programmes. The main objective is to serve the producer, the consumer and the seed industry by providing information on seed quality. Based on the results, whether the seed lot is to be accepted or not is decided (http://Agritech.tnau.ac.in/seed/Seed_seedtesting.html).

19.5.3 Physical Purity Testing

Physical purity analysis tells us the proportion of pure seed component in the seed lot as well as the proportion of other crop seeds, weed seeds and inert matter by weight in percentage for which seed standards have been prescribed. Thus, it helps in:

  1. 1.

    Improving the plant stand (by increasing the pure seed component)

  2. 2.

    Raising a pure crop (by eliminating other crop seeds and weed seeds)

  3. 3.

    Raising a disease-free crop (by eliminating inert matter)

  4. 4.

    Using of seed drill (by selecting uniform particles)

19.5.3.1 Obtaining Working Sample

The working sample is the whole of the submitted sample or a subsample thereof, on which one of the seed quality tests is made. Boerner or soil-type seed divider should be used to homogenise the submitted sample before reducing it to the size of working sample.

The following guidelines need to be followed:

  1. 1.

    Check the cleanliness of the divider and the container.

  2. 2.

    Pour the entire contents of the submitted sample into the hopper of the divider.

  3. 3.

    Allow the content of the submitted sample to pass through the main body of the divider. In case of ‘soil-type’ seed divider, this can be accomplished by tilting the hopper over the body of the divider, while in the case of ‘Boerner’ divider, by opening the gate valve situated at the base of the hopper.

  4. 4.

    Recombine the contents of both sample receiving pans and again pass it through the divider.

  5. 5.

    Repeat this process twice in order to homogenise the submitted sample.

  6. 6.

    Divide the submitted sample.

  7. 7.

    Set aside the contents of one container.

  8. 8.

    Divide the contents of the other container subsequently till the weight of working sample is obtained.

19.5.3.2 Separation

  1. (a)

    Clean the work board, sample and purity dishes before starting the separation.

  2. (b)

    Examine the working sample to determine the use of particular aid such as blower or sieves for making separation.

  3. (c)

    After preliminary separation with the help of sieves or blower, place and spread the retained or heavier portion on the purity work board.

  4. (d)

    With the help of spatula or forceps, draw working sample into thin line and examine each particle individually, the criteria used being the external appearance (shape, size, colour, gloss, surface texture) and/or appearance in transmitter light.

  5. (e)

    Separate out impurities such as other crop seeds, weed seeds and inert matter and place the impurities separately in purity dishes, leaving only the pure seed on the purity board.

  6. (f)

    Seed enclosed in fruits other than those indicated in pure seed should be separated and the detached empty fruit/appendages classed as inert matter.

  7. (g)

    Collect the pure seed in the sample pan.

  8. (h)

    Put the lighter portion of the work board and examine under magnification for further separating into the requisite classes (other crop seeds, weed seeds and inert matter).

  9. (i)

    After separation, identify the other crop seeds and weed seeds and record their names on the analysis card. The kind of inert matter present in the sample should also be identified and recorded.

  10. (j)

    Weigh each component, pure seed and other crop seeds, weed seeds and inert matter in grams to the number of decimal places shown below:

    SL. no.

    Wt. of working sample (g)

    No. of decimal place required

    Example

    1.

    Less than 1

    4

    0.9025

    2.

    1–9.990

    3

    9.025

    3.

    10–99.99

    2

    90.25

    4.

    100–999.99

    1

    902.5

    5.

    1,000 or more

    0

    1,025

  11. (k)

    Calculate the percentage by weight of each component to one decimal place only, basing the percentage on the sum of the weight of all the four components. If any component is less than 0.05 %, record it as ‘Trace’. Component of 0.05–0.1 % is reported as 0′, 1 %.

19.5.3.3 Reporting the Results

The results of purity test must be given to one decimal place only, and the percentage of all components must total 100. If the result for a component is nil, this must be shown as 0.0 % in the appropriate space of the report form. The report should also include the kind of inert matter and the Latin names of the crop seed and weed seed found in the sample (Seednet.ap.nic.in/stl/htmlpages/physicalpuritytesting.htm).

19.5.4 Seed Germination Test

The purpose of laboratory testing of seed germination is to assess seed quality or viability and to predict performance of the seed and seedling in the field. A notified laboratory under the Seeds Act or qualified laboratory of ISTA for testing seeds must test seed processed for sale. The ultimate aim of testing the germination in seed-testing laboratory is to obtain information about the planting value of the seed sample and by inference the quality of the seed lot. In addition, the laboratory germination results are also required for comparing the performance potential or superiority of the different seed lots. In general, the farmers, seedsmen and public agencies use the germination results for the following purposes:

  1. 1.

    Sowing purposes, with a view to decide the seed rate to achieve desired field establishment

  2. 2.

    Labelling purposes

  3. 3.

    Seed certification purposes

  4. 4.

    Seed Act and law enforcement purposes

In seed testing, germination has been defined as ‘the emergence and development from the seed embryo of those essential structures which, for the kind of seed tested, indicate its ability to develop into a normal plant under favourable conditions in soil’. The seedlings devoid of an essential structure, showing weak or unbalanced development, decay or damage affecting the normal development of seedling, are not considered in calculating the germination percentage. Factors that can affect the performance of seed in germination tests include diseased seed, old seed, mechanically damaged seed, seed stored under high moisture and excessive heating of seed during storage or drying.

19.5.4.1 Laboratory Procedures

The working sample or germination test consists of 400 pure seeds randomly drawn either manually or with the help of counting devices. The seed for germination test must be drawn as follows in accordance with the following two situations:

  1. 1.

    When both purity and germination tests are required:

    1. (a)

      Seeds for germination tests must be taken from the pure seed fraction after conducting the physical purity analysis.

    2. (b)

      The counting of the seed must be made without discrimination as to the size and appearance.

  2. 2.

    Only germination test is required:

    1. (a)

      If the percentage of pure seed is estimated or determined to be above 98 %, the pure seed for germination test shall be taken indiscriminately from a representative portion of the submitted sample.

    2. (b)

      If the pure seed is found to be less than 98 %, the seeds for germination test must be obtained by separating the sample into two components, namely:

      1. (i)

        The pure seed

      2. (ii)

        Seeds of other species and inert matter

For this purpose, at least one-fourth of the quantity required for regular purity analysis must be used after proper mixing and dividing the submitted sample.

19.5.4.2 Number of Replication

Four replications of 100 seeds or a minimum of 3 replications of 100 seeds may be used under unavoidable situations or 8 or 6 replications of 50 seeds or 16/12 replication of 25 seeds according to the kind and size of containers.

19.5.4.3 Substrata for Germination Testing

After placing the seeds on the prescribed substrata, the test should be transferred to the prescribed controlled temperature condition maintained in the cabinet or walk-in germinator for a prescribed period, which varies according to the species (ISTA Seed Testing Rules). In the rules for seed testing, two kinds of temperature conditions are provided. A single numerical indicates the constant temperature where as numericals separated by a dash (-) indicates an alternating temperature. The daily alternation of temperature is brought out manually either by transferring the test from one germinator to another or by changing the temperature of the chamber as in the case of automatic seed germinator.

19.5.4.4 Evaluation of Germination Test

The germination tests need to be evaluated on the expiry of the germination period, which varies according to the kind of seed. However, the seed analyst may terminate the germination test on or before the final count day or extend the test beyond the period depending on the situation. First and second counts are usually taken in the case of top of paper (TP) and between paper (BP) media. At the first and subsequent counts, only normal and dead seeds (which are source of infection) are removed and recorded.

While evaluating the germination test, the seedlings and seeds are categorised into normal seedlings, abnormal seedlings, dead seeds and fresh ungerminated and hard seeds. It may also be necessary to remove the seed coat and separate the cotyledons in order to examine the plumule in species where essential structures are still enclosed at the end of the test.

19.5.4.5 Calculation and Expression of Result

Results are expressed as percentage by number.

$$ \mathrm{Germination}\;\left(\%\right)=\left[\mathrm{number}\;\mathrm{of}\;\mathrm{seeds}\;\mathrm{germinated}/\mathrm{number}\;\mathrm{seeds}\;\mathrm{kept}\right]\times 100 $$

When four 100-seed replicates of a test are within the maximum tolerated range, the average represents the percentage germination to be reported on the analysis certificate. The average percentage is calculated to the nearest whole number. The total % of all the category of seeds (normal, abnormal, dead hard, fresh ungerminated) should be 100.

19.5.4.6 Retesting

If the results of a test are considered unsatisfactory, it will not be reported, and a second test will be made by the same method or by an alternative method under the following circumstances:

  • Replicate performance is out of tolerance.

  • Results being inaccurate due to wrong evaluation of seedlings or counting or errors in test conditions.

  • Dormancy persistence or phytotoxicity or spread of fungi or bacteria. The average of the two tests shall be reported.

19.5.4.7 Use of Tolerances

The result of a germination test can be relied upon only if the difference between the highest and the lowest replicates is within accepted tolerances. To decide if two test results of the same sample are compatible again, the tolerance table is used (Agrawal and Dadlani 1995).

19.5.5 Seed Vigour Testing

Vigour testing does not only measure the percentage of viable seed in a sample, it also reflects the ability of those seeds to produce normal seedlings under less than optimum or adverse growing conditions similar to those which may occur in the field. Seeds may be classified as viable in a germination test which provides optimum temperature, moisture and light conditions to the growing seedlings; however, they may not be capable of continuing growth and completing their life cycle under a wide range of field conditions. Generally, seeds start to lose vigour before they lose their ability to germinate; therefore vigour testing is an important practice in seed production programmes.

Testing for vigour becomes more important for carryover seeds, especially if seeds were stored under unknown conditions or under unfavourable storage conditions. Seed vigour testing is also used as indicator of the storage potential of a seed lot and in ranking various seed lots with different qualities.

19.5.5.1 Uses of Seed Vigour Test

  1. 1.

    Vigour tests are commonly used by seed production companies to establish ‘in-house’ seed quality standards and to monitor seed quality during the various phases of seed production and processing.

  2. 2.

    Seed store managers may use vigour test results to make better informed decisions about the suitability of seed lots for storage, the possible length of storage time and the storage conditions required.

  3. 3.

    Seed exporters can use vigour information to decide which seed lots can withstand the rigours of transport and thus be expected to arrive in the importing country with quality unimpaired.

  4. 4.

    For the ultimate consumer, the farmer, it would be advantageous to know the vigour status of each high-germinating seed lot before making any decision as to which one to buy.

  5. 5.

    Breeding programmes can employ vigour tests to develop cultivars with improved seed performance.

19.5.5.1.1 Hiltner Test

Hiltner test was initially developed to detect seed-borne infection by Fusarium spp. It was subsequently developed as a vigour test when it was shown to reflect defects that prevent normal seedlings other than those resulting from seed-borne infection. Seeds having low vigour cannot withstand physical stress during germination. Hence, seeds are sown within layers of sterile brick grit or course sand with a particle size of 2–3 mm. This provides a mechanical barrier through which seeds must penetrate in order to emerge. The emergence of normal seedlings is considered to indicate seed vigour status.

19.5.5.1.2 Cold Test

The cold test simulates early spring field conditions by germinating the seeds in wet soils (70 % water holding capacity) and incubating them at 5–10 °C/41–51 °F for a specified period. At the end of the cold period, the test is transferred to a favourable temperature for germination (e.g. 25 °C/77 °F in the case of sweetcorn). The percentage of normal seedlings is considered as an indication of seed vigour. Vigorous seeds germinate better under cold environments.

19.5.5.1.3 Accelerated Ageing Test (AAT)

The principle of this test is to stress seeds with high temperatures of (40–45 °C/130–139 °F) and near 100 % relative humidity (RH) for varying lengths of time, depending on the kind of seeds, after which a germination test is made. High-vigour seeds are expected to tolerate high temperatures and humidity and retain their capability to produce normal seedlings in the germination test.

19.5.5.1.4 Electrical Conductivity Test

This test measures the integrity of cell membranes, which is correlated with seed vigour. It is well established that this test is useful for garden beans and peas. It has been also reported that the conductivity test results are significantly correlated with field emergence for corn and soybean. As seeds lose vigour, nutrients exude from their membranes, and so low-quality seeds leak electrolytes such as amino acids and organic acids, while high-quality seeds contain their nutrients within well-structured membranes. Therefore, seeds with higher conductivity measurement are an indication of low-quality seeds and vice versa.

19.5.5.1.5 Seedling Vigour Classification Test (SVCT)

This vigour test is an expansion of the standard germination test (SGT). The normal seedlings obtained from the SGT results are further classified into ‘strong’ and ‘weak’ categories. This test has been used for corn, garden beans, soybean, cotton, peanuts and other crops.

Seedlings have four significant morphological sites for evaluating vigour:

  1. A.

    Root system

  2. B.

    Hypocotyl (the embryonic axis between cotyledons and root)

  3. C.

    Cotyledons (storage tissue of reserve food for seedling development)

  4. D.

    Epicotyl (the embryonic axis above the cotyledons)

In this test, seedlings are classified as ‘strong’ if the above four areas are well developed and free from defects, which is an indication of satisfactory performance over a wide range of field conditions. On the other hand, normal seedlings with some deficiencies such as missing part of the root, one cotyledon missing, hypocotyl with breaks, lesions, necrosis, twisting or curling are classified as ‘weak’.

19.5.5.1.6 Paper Piercing Test

The principle of paper piercing test is similar to that of brick gravel test. High-vigour seed lots are expected to produce strong seedlings which can pierce a particular type of paper, while seedlings of poor vigour lots may not be able to pierce the paper. Therefore, the seedlings which emerge by piercing the paper are more vigorous than those which are not able to emerge through the paper.

19.5.5.1.7 RQ Test

During the first few hours of imbibition of water, respiration rate increases which is highly associated with subsequent seedling growth rate (maize, wheat, rice, lima bean, etc.). During respiration, the ratio of volume of CO2 evolved to the volume of O2 consumed per unit time is termed as RQ and it is related to seed vigour. The rate of gas exchange is measured in a respirometer called ‘Warburg respirometer’.

19.5.6 Genetic Purity Testing

19.5.6.1 Grow-Out Test

A seed is said to be genetically pure if it possesses all the genetic qualities that the breeder has placed in the variety. With any deterioration in the genetic make-up of the variety during seed multiplication and distribution cycle, there would definitely be proportionate decrease in its performance, e.g. yield, disease/pest resistance, etc. Genetic purity of a seed lot is determined on the basis of distinct morphological characters of the variety expressed at seed, seedling and plant level by comparing its submitted sample with authentic sample under identical environmental situation (Li-Wang Liu et al. 2007; Dongre and Parkhi 2005).

19.5.6.2 Chemical Tests for Species and Cultivar Identification

The chemical tests are spot tests and useful in identification by change in seed colour as well as solution due to added chemicals. The chemical tests, viz. phenol test, peroxidase test, NaOH and KOH test, ferrous sulphate test and seedling response to various chemicals, have been proved to be quite useful in detecting varietal mixtures and grouping of large number of genotypes into distinct classes. These chemical tests are very quick, easy and reproducible, and these tests provide supportive evidence for morphological evaluation of seeds (Agrawal and Dadlani 1995). Protein gel electrophoresis method is the most commonly employed biochemical test for species and cultivar identification. Among the biochemical techniques, SDS-PAGE is an economical, simple and extensively used biochemical technique for describing the seed protein diversity of crop germplasm (Fufa et al. 2005).

Advantages

  1. 1.

    These tests can be easily done by a laboratory technician on large scale in a seed-testing laboratory in the shortest period.

  2. 2.

    They are relatively inexpensive.

  3. 3.

    The test permits detection of percentage admixture of other types.

19.5.6.3 Molecular Tests for Species and Cultivar Identification

Repeatability and accuracy of results using biochemical markers are subject to question, leading to use of DNA molecular markers (RAPD), particularly the codominant markers (SSRs). Simple sequence repeat (SSR) markers are of great importance for rapid assessment of hybrid and parental line seed purity (Sundaram et al. 2006; Pallavi et al. 2011).

19.5.7 Testing for Seed Moisture Content

The seed moisture content (mc) is the amount of water in the seed. It is usually expressed as a percentage on wet weight basis in any seed-testing laboratory. The seed moisture content is the most vital parameter, which influences the seed quality and storage life of the seed. Seed moisture content is closely associated with several aspects of physiological seed quality. For example, it is related to seed maturity, optimum harvest time, mechanical damage, economics of artificial seed drying, seed longevity and insect and pathogen infestation. The objective is to determine the moisture content of seed by methods suitable for routine use. The optimum method for moisture testing depends upon chemical composition of seed, seed structure, moisture content level, degree of accuracy and precision required, constraints of time, technical expertise and cost.

The ideal method could be that it is adapted to all seeds, measures moisture content from 0 % to100 %, is reproducible, requires less training and is low in cost. It is impossible to combine all these. However, in order to measure the moisture content of seeds, methods can be broadly grouped in two categories: (a) direct method and (b) indirect method.

19.5.7.1 Direct Method

Under this category, the seed moisture content is measured directly by loss or gain in seed weight. These are desiccation method, phosphorus pentoxide method, oven-drying method, vacuum-drying method, distillation method, Karl Fischer’s method, direct weighing balance and microwave oven method.

19.5.7.2 Indirect Method

These are not so accurate; estimation is approximate, but convenient and quick in use. These are frequently used at seed processing plants. These measure other physical parameters like electrical conductivity or electrical resistance of the moisture present in the seed. Values are measured with the help of seed moisture metres, and these values are transformed into seed moisture content with the help of calibration charts, for each species, against standard air-oven method or basic reference method.

Above all, Karl Fischer’s method has been considered as the most accurate and the basic reference method for standardising other methods of seed moisture determination. The constant temperature oven-drying method is the only practical method approved by International Seed Testing Association (ISTA) and other organisations to be used for routine seed moisture determination in a seed-testing laboratory.

19.5.7.3 Constant Temperature Oven-Drying Method

The constant temperature oven-drying method is broadly grouped into two categories:

  1. 1.

    Low constant temperature oven method

  2. 2.

    High constant temperature oven method

Low constant temperature oven method: This method has been recommended for seed of the species rich in oil content or volatile substances. In this method, the pre-weighed moisture bottles along with seed material are placed in an oven maintaining a temperature of 103 °C. Seeds are dried at this temperature for 17 ± 1 h. The relative humidity of the ambient air in the laboratory must be less than 70 % when the moisture determination is carried out.

High constant temperature oven method: The procedure is the same as above except that the oven is maintained at a temperature of 130–133 °C. The sample is dried to a period of 4 h for Zea mays, 2 h for other cereals and 1 h for other species. In this method there is no special requirement pertaining to the relative humidity of the ambient air in the laboratory during moisture determination.

19.5.7.4 Seed Moisture Testing Procedure

  1. 1.

    Seed moisture determination be carried out in duplicate on two independently drawn working samples.

  2. 2.

    Weigh each bottle with an accuracy of 1 or 0.1 mg.

  3. 3.

    First, weigh the empty bottle/container with its cover.

  4. 4.

    Grind the seed material evenly using any grinder/grinding mill that does not cause heating and/or loss of moisture content.

  5. 5.

    Mix thoroughly the submitted sample, using spoon, and transfer small portions (4–5 g) of seed samples directly into weighing bottles/containers by even distribution on bottom of the containers.

  6. 6.

    After weighing, remove the cover or lid of the weighing bottles/containers.

  7. 7.

    Place the weighing bottles/containers in an oven, already heated to or maintained in the desired temperature, for the recommended period.

  8. 8.

    At the end of seed drying period, weighing bottles/containers must be closed with its lid/cover.

  9. 9.

    Transfer the weighing bottles/containers to the desiccators having silica gel (self-indicating blue) to cool down for 40–45 min.

  10. 10.

    Weigh again the cooled weighing bottles/containers.

  11. 11.

    Calculate the seed moisture content.

The moisture content as a percentage by weight (fresh weight basis) is calculated to one decimal place, by using of the formulae:

$$ \begin{array}{l}\mathrm{Percentage}\;\mathrm{seed}\;\mathrm{moisture}\;\mathrm{content}\left(\mathrm{m}.\mathrm{c}\right)=\\ {}\left[{M}_2-{M}_3/{M}_2-{M}_1\right]\times 100\end{array} $$

where

  • M 1 = weight of the weighing bottle/container with cover in gm

  • M 2 = weight of the weighing bottle/container with cover and seeds before drying

  • M 3 = weight of the weighing bottle/container with cover and seeds after drying

    {Note: The seed moisture determination must be done in two replicates, with precise weighing (i.e. up to three decimal places) using lightweight weighing bottles/containers.}

If the seed is pre-dried or dried in two steps, the seed moisture content is calculated from the results obtained in the first (pre-dried) and second stages of seed drying, using the following formula, and expressed as percentages, as under:

$$ \begin{array}{l}\mathrm{Percentage}\;\mathrm{seed}\;\mathrm{moisture}\;\mathrm{c}\mathrm{ontent}\left(\mathrm{m}\mathrm{c}\right)=\\ {}\frac{\left[\left({S}_1+{S}_2\right)-\left({S}_{\mathrm{I}}*{S}_2\right)\right]}{100}\end{array} $$

where

  • S 1 = is the moisture loss in the first stage

  • S 2 = is the moisture loss in the second stage

19.5.7.5 Reporting of Results

Seed moisture content must be reported to the nearest 0.1 % on ISTA analysis certificate. If the seed moisture content is determined using any moisture metre, the brand name and type of the equipment must be mentioned on the analysis certificate, under the column ‘other determinations’; reporting of range for which the moisture metre is calibrated is another requirement on seed analysis certificate.

19.6 Seed Production System in India

The Indian seed programme largely adheres to the limited generation system for seed multiplication in a phased manner. Generation system of seed multiplication is nothing but the production of a particular class of seed from specific class of seed up to certified seed stage. The choice of a proper seed multiplication model is the key to further success of a seed programme. This basically depends upon (a) the rate of genetic deterioration, (b) seed multiplication ratio and (c) total seed demand (seed replacement rate). The system recognises three generations, namely, breeder, foundation and certified seeds, and provides adequate safeguards for quality assurance in the seed multiplication chain to maintain the purity of the variety as it flows from the breeder to the farmer.

19.6.1 Nucleus Seed

The initial handful of seeds are obtained from selected individual plants of a particular variety, for the purpose of purifying and maintaining that variety, by the originating plant breeder.

19.6.2 Breeder Seed

Breeder seed is the progeny of nucleus seed of a variety and is produced by the originating breeder or by a sponsored breeder. This provides for initial and recurring increase of foundation seed. Breeder seed is monitored by a joint inspection team of scientists and officials of certification agency and National Seed Corporation (NSC). The genetic purity of breeder seed crop should be maintained at 100 %. Breeder seed production is the mandate of the Indian Council of Agricultural Research (ICAR) and is being undertaken with the help of (1) ICAR research institutions, national research centres and All India Coordinated Research Project of different crops, (2) state agricultural universities (SAUs), (3) sponsored breeders recognised by selected state seed corporations and (4) non-governmental organisations.

19.6.3 Foundation Seed

Foundation seed is the progeny of breeder seed and is required to be produced from breeder seed or from foundation seed which can be clearly traced to breeder seed. The responsibility for production of foundation seed has been entrusted to the NSC, State Farm Corporation of India (SFCI), state seed corporation, state departments of agriculture and private seed producers, who have the necessary infrastructure facilities. Foundation seed is required to meet the standards of seed certification prescribed in the Indian Minimum Seed Certification Standards, both at the field and laboratory testing.

19.6.4 Certified Seed

Certified seed is the progeny of foundation seed and must meet the standards of seed certification prescribed in the Indian Minimum Seed Certification Standards, 1988. In the case of self-pollinated crops, certified seeds can also be produced from certified seeds provided it does not go beyond three generations from foundation seed stage-I.

The production and distribution of quality/certified seeds is primarily the responsibility of the state governments. Certified seed production is organised through state seed corporation, departmental agricultural farms, cooperatives, etc. The distribution of seeds is undertaken through a number of channels, i.e. departmental outlets at block and village level, cooperatives, outlets of seed corporations, private dealers, etc. NSC markets its seeds through its own marketing network and also through its dealer network. SFCI markets its seeds mainly through the state departments of agriculture and the state seed corporations. The production of certified seed by NSC and state seed corporations is mainly organised through contract growing arrangements with progressive farmers. SFCI undertakes seed production on its own farms. The private sector has also started to play an important role in the supply of quality seeds of vegetables and crops like hybrid maize, sorghum, bajra, cotton, castor, sunflower, paddy, etc.

19.7 Seed Certification

In general, seed certification is a process designed to maintain and make available to the general public continuous supply of high-quality seeds and propagating materials of notified kinds and varieties of crops so grown and distributed to ensure the physical identity and genetic purity. Seed certification is a legally sanctioned system for quality control of seed multiplication and production.

19.7.1 Objectives of Seed Certification

The main objective of the seed certification is to ensure the acceptable standards of seed viability, vigour, purity and seed health. A well-organised seed certification should help in accomplishing the following three primary objectives.

  • The systematic increase of superior varieties

  • The identification of new varieties and their rapid increase under appropriate and generally accepted names

  • Provision for continuous supply of comparable material by careful maintenance

19.7.2 Eligibility Requirements for Certification

Any variety to become eligible for seed certification should meet the following requirements:

  1. 1.

    General requirements

  2. 2.

    Field standards

  3. 3.

    Specific requirements

  4. 4.

    Seed standards

The variety selected for certified seed production should be a notified variety under Section 5 of the Indian Seed Act, 1966, and it should be in the production chain and its pedigree should be traceable.

In a seed quality control programme through seed certification, the minimum seed certification standards, in fact, are the minimum standard conditions which must be met. The minimum seed certification standards thus are the standards required for the certification of seeds by the certification agencies. The certification standards in force in India are called the Indian Minimum Seed Certification Standards. These were published by the Central Seed Certification Board. As a general principle, these standards have been kept at the level, which demand scrupulous attention of the certified seed growers, but at the same time are practical enough that these can be met also. The minimum seed certification standards can be broadly grouped into two groups:

  1. 1.

    The general seed certification standard aims at outlining the general requirements for the production of genetically pure good-quality seed. These standards prescribed the procedure for certified seed production so that maximum genetic purity and good quality of the seed is ensured.

  2. 2.

    Specific crop standard consists of field standards and seed standards. The field standards consist of:

    1. (a)

      The minimum preceding crop requirement specified to minimise genetic contamination from the diseases volunteer plants.

    2. (b)

      The minimum isolation requirement specified to minimise seed-borne diseases.

    3. (c)

      The number of field inspection and specified stage of crop described to ensure verification of genetic purity and other quality factors.

19.7.3 Seed Standard

Seed standard consists of:

  1. (a)

    The minimum percentage of pure seeds and maximum permissible limits for inert matter, other crop seeds have been prescribed.

  2. (b)

    The maximum permissible limits for objectionable weeds, seeds infected by seed-borne diseases have been prescribed to ensure good seed health.

  3. (c)

    The maximum permissible limits for moisture content have been prescribed for the safe storage of seeds.

The two combined sets of standards constitute the minimum seed certification standards for seed certification.

19.7.4 Seed Certification Agencies

Seeds Act, 1966, provides for the establishment of seed certification agencies in each state. Seed certification agency should function on the following broad principles:

  • Seed certification agency should be an autonomous body.

  • Seed certification agency should not involve itself in the production and marketing of seeds.

  • The seed certification standards and procedures adapted by seed certification agency should be uniform throughout the country.

  • Seed certification agency should have close linkage with the technical and other related institutions.

  • Its long-term objective should be to operate on no-profit, no-loss basis.

  • Adequate staff trained in seed certification should be maintained by the certification agency.

  • It should have provision for creating adequate facilities for ensuring timely and thorough inspections.

  • It should serve the interests of seed producers and farmers/users.

19.7.5 Seed Certification Control Measures

Seed source verification is the first step in seed certification programme. Unless the seed is from approved source and of designated class, certification agency will not accept the seed field for certification, thereby ensuring the use of high quality true to type seed for sowing of seed crops.

19.7.5.1 Field Inspection

In the evaluation of the growing crop in the field for varietal purity, isolation of seed crop is to prevent outcross, physical admixtures and disease dissemination and also ensure crop condition as regards the spread of designated diseases and the presence of objectionable weed plants.

19.7.5.2 Sample Inspection

Assessing the planting value of the seeds by laboratory tests. Certification agency draws representative samples from the seeds produced under certification programme and subject them to germination and other purity tests required for conforming varietal purity.

19.7.5.3 Bulk Inspection

Under certification programme provision has been made for bulk inspection. Hence, the evaluation of the lot for the purpose of checking homogeneity of the bulk seed produced as compared with the standard sample is carried out. This gives an idea about the genuinity of lot and sample.

19.7.5.4 Control Plot Testing

Here the samples drawn from the source and final seed produced are grown side by side along with the standard samples of the variety in question. By comparison it can be determined whether the varietal purity and health of the produced seed are equal to the results based on field inspection.

19.7.5.5 Grow-Out Test

Evaluation of the seeds for their genuineness to species or varieties or seed-borne infection. Here the samples drawn from the lots are grown in the field along with the standard checks. Growing plants are observed for the varietal purity. Grow-out test helps in the elimination of the substandard seed lots of the seed crop in the field to verify its conformity to the prescribed field standards (http://seednet.gov.in/material/IndianSeedSector.htm#Seed Certification System in India).

19.8 Seed Legislation

Development of improved crop varieties is vital for sustained increase in agriculture production and productivity. Timely supply of quality seed is equally significant since the contribution of quality seed alone is estimated to be 15–20 % of the total crop production. India with a population of more than one billion and an arable area of 168 million hectares has one of the largest potential seed market in the world. The total Indian seed market valued around $500 million 5 years back (Gadwal 2003), but it values $1 billion presently with large portion of seed trade involving local exchanges of established varieties or farmer-bred seeds. The total amount of certified seeds produced is only 8 % (Gadwal 2003) of total seed sown each year. Therefore, it is imperative to increase the production and distribution of quality seeds. Seed quality attains more significance in view of emerging biotic and abiotic stresses, issues related to quality and phytosanitary measures, competition in domestic and international markets and emerging food needs.

Measures of seed legislation with respect to quantity and quality were initiated in the country by establishment of National Seed Corporation during 1963 under Ministry of Agriculture. The seed sector in India during the period was dominated by the public sector. The National Seed Corporation was the central body to produce seeds of superior dwarf varieties in rice and wheat and superior hybrids in maize, pearl millet and sorghum. This was followed by various seed legislations enacted by the Government of India, the details of which have been enumerated in the following pages. Further, AICRP-National Seed Project during 1979 (NSP) was undertaken by the Indian Government. The project resulted in achieving breeder seed production surpassing the indents in all major crops. Recently, the Government’s decision to embrace biotechnology as a means of achieving food security has made seed quality an important aspect in R&D and business sector in India such as ‘approval for commercial cultivation of Bt cotton’ in the year 2002. Several leading multinational seed companies have entered the seed market, and at present the composition of the seed industry by volume of turnover has reportedly reached a ratio of 60:40 between the private and public sectors.

Since most of the farming community is illiterate or semi-literate, it is the responsibility of the Government to frame rules that govern the production and distribution of quality seeds to the farming community. Though the Seed Act had been implemented in European countries at the end of eighteenth century, India didn’t have an act to designate seed quality parameters. This void was fulfilled during 1966, when the Seed Act was formed and followed by Seed Rules in 1968. Both were adopted during 1969 for the whole of India. Amendments were made subsequently for the Seed Act during the years 1972, 1973, 1974 and 1981. With new varieties coming into the agricultural scenario, the Seed Control Order was formed insisting on compulsory licensing of the dealer. This was made even more stringent by bringing the seeds under the Essential Commodity Act, 1955. To help multinational corporation in utilising the manpower and knowledge base of our country, the Plants, Varieties and Fruits Order was passed during 1989 and amended subsequently during 1998, 2000 and 2001. Finally the order was revised by another order, Plant Quarantine (Regulation of Import into India) Order in 2003. Signing of WTO in 1995 paved the way for private research and development of varieties. In order to regulate such varieties, the protection of Plant Varieties and Farmers’ Right Act was passed in 2001 which was followed by National Seed Policy, 2002, and Seeds Bill, 2004.

19.8.1 Protection of Plant Varieties and Farmers Right Act, 2001

Global realisation on the role of plant genetic resources in development of superior crop varieties and use of many traditionally grown plants in development of medicines and various industrial applications raised concerns for Conservation of Biological Diversity (CBD) which came into force in the year 1993. The Government of India felt the need to provide protection to plant varieties which have tremendous commercial value after India became signatory to the Trade-Related Aspects of Intellectual Property Rights Agreement (TRIPS) in the year 1994. The TRIPS agreement required the member countries to provide for protection of plant varieties either by a patent or by an effective sui generis system or by any combination thereof. The sui generis system for protection of plant varieties was developed by India, integrating the rights of breeders, farmers and village communities. The Protection of Plant Varieties and Farmers Right Act was thus formulated in the year 2001 (Pratibha Brahmi et al. 2003; Ramamoorthy et al. 2006).

19.8.1.1 The Main Objectives of the Act

  • To recognise and protect the rights of farmers for their contribution made at any time in conserving, improving and making available plant genetic resources for the development of new plant varieties

  • To encourage the development of new varieties of plants for accelerated agricultural development

  • To accelerate the agricultural development in the country and protect Plant Breeders’ Rights (PBR) and to stimulate investment in research and development (R&D) both in the public and private sectors for breeding new plant varieties

  • To facilitate the growth of the seed industry, which will ensure the availability of good-quality seed and plant material to farmers

19.8.1.2 Salient Features of the Act

The registration of a plant variety under the PPVFR Act is a legal process, and as per the act it is compulsory. This process establishes the Plant Breeders’ Rights (PBR) on the plant variety in favour of the applicant(s). PBR is a legal ownership right granted on a plant variety. Ownership of PBR is not permanent but only for a specific period (15–18 years). PBR can be inheritable by succession, transferable and saleable. The act prescribes the following:

  1. 1.

    Who are eligible for registration of plant variety.

  2. 2.

    The crop varieties that can be registered: these include new varieties that are novel, distinct, uniform and stable.

  3. 3.

    Extant varieties that were in existence before the act.

  4. 4.

    Farmers’ varieties: those that are traditionally cultivated and evolved by the farmers in their fields or a wild relative or land race or a variety about which the farmers possess knowledge. The act also specifies varieties that are to be excluded from registration.

19.8.1.2.1 Process of Varietal Registration
  1. 1.

    Submission of application to the registrar in the prescribed proforma

  2. 2.

    Deposition of seed to National Gene Bank for conducting DUS test

  3. 3.

    Advertisement of application to call for any opposition

  4. 4.

    Issue of certification of registration

  5. 5.

    Publication of list of registered varieties

  6. 6.

    Breeder to deposit the seeds/propagating material of registered varieties to National Gene Bank

  7. 7.

    Registration to confer PBR

A National Register of Plant Varieties shall be maintained at the Head Office of the Plant Variety Registry in the Authority. The register will contain the name of registered plant variety with the name, addresses and rights of their breeders and particulars of the denominations of the registered variety.

19.8.1.2.2 Breeders’ Rights

Breeder of a registered variety shall have an exclusive right to produce, sell, market, distribute, import or export the variety. In the case of an extant variety, unless a breeder or his successor establishes his or her right, the central government and, in cases where such extant variety is notified for a state or for any area thereof under Section 5 of the Seeds Act, 1966 (54 of 1966), the state government shall be deemed to be the owner of such rights.

19.8.1.2.3 Researchers’ Rights
  1. (a)

    The use of any variety registered under this Act by any person using such variety for conducting experiment or research

  2. (b)

    The use of a variety by any person as an initial source of variety for the purpose of creating other varieties

Provided that the authorisation of the breeder of a registered variety is required where the repeated use of such variety as a parental line is necessary for commercial production of such other newly developed variety.

19.8.1.2.4 Establishment of ‘National Gene Fund’ (NGF)

A National Gene Fund (NGF) shall be established under this act, receipts of which include benefit shares, registration fee, compensation payments and other grants from national and international organisations. The NGF will be utilised for promotion of on-farm and ex situ conservation by individuals, communities, panchayats and institutions, for rewarding and recognising conservation undertaken by individuals and communities and for disbursing the pronounced benefit shares and compensations.

19.8.1.2.5 Benefit Sharing

On registration of the variety, any person or group of persons may submit his or her claim of benefit sharing in the prescribed form, and with prescribed fee to the authority if his or her material has been used in the development of that variety, the authority shall take the decision on the matter after considering the following points:

  1. (a)

    The extent and nature of use of the genetic material of the claimant in the development of the variety relating to which the benefit sharing has been claimed

  2. (b)

    The commercial utility and demand in the market of the variety relating to which the benefit sharing has been claimed

19.8.1.2.6 Gene Bank

A National Gene Bank will be established by the authority to maintain the seed samples of the registered varieties for the entire period of protection under the act. The applicant of the registered variety shall rejuvenate the seed if so desired by the registrar.

19.8.2 National Seed Policy, 2002

Indian agriculture has made enormous strides in the past 50 years, raising food grain production from 50 million tonnes to over 230 million tonnes. In the process, the country has progressed from a situation of food shortages and imports to one of surpluses and exports. Having achieved food sufficiency, the aim now is to achieve food and nutritional security at the household level. The seed sector has made impressive progress over the last three decades. The Seeds Act, 1966, and Seed Control Order (1983) promulgated thereunder and the New Policy on Seeds Development (1988) form the basis of promotion and regulation of the seed industry. Far-reaching changes, however, have taken place in the national economic and agricultural scenario and in the international environment since the enactment of the existing seed legislation and the announcement of the 1988 policy.

19.8.2.1 Aims and Objectives

It has become evident that in order to achieve the food production targets for the future, a major effort will be required to enhance the seed replacement rates of various crops. This would require a major increase in the production of quality seeds, in which the private sector is expected to play a major role. At the same time, private and public sector seed organisations at both central and state levels will be expected to adopt economic pricing policies which would seek to realise the true cost of production. The creation of a facilitative climate for growth of a competitive and localised seed industry, encouragement of import of useful germplasm and boosting of exports are core elements of the agricultural strategy of the new millennium.

Biotechnology will be a key factor in agricultural development in the coming decades. Genetic engineering/modification techniques hold enormous promise in developing crop varieties with a higher level of tolerance to biotic and abiotic stresses. A conducive atmosphere for application of frontier sciences in varietal development and for enhanced investments in research and development is a pressing requirement. At the same time, concerns relating to possible harm to human and animal health and biosafety, as well as interests of farmers, must be addressed.

Globalisation and economic liberalisation have opened up new opportunities as well as challenges. The main objectives of the National Seeds Policy (2002), therefore, are the provision of an appropriate climate for the seed industry to utilise available and prospective opportunities, safeguarding of the interests of Indian farmers and the conservation of agro-biodiversity. While unnecessary regulation needs to be dismantled, it must be ensured that gullible farmers are not exploited by unscrupulous elements. A regulatory system of a new genre is, therefore, needed, which will encompass quality assurance mechanisms coupled with facilitation of a vibrant and responsible seed industry. The National Seed Policy, 2002, covers ten thrust areas which are as follows (http://Agricoop.nic.in/seedpolicy.htm):

  • Varietal development and plant variety protection

  • Seed production

  • Quality assurance

  • Seed distribution and marketing

  • Infrastructure facilities

  • Transgenic plant varieties

  • Import of seed and planting material

  • Export of seeds

  • Promotion of domestic seed industry

  • Strengthening of monitoring system

19.9 Seed Storage

The ability of seed to tolerate moisture loss allows the seed to maintain the viability in dry state. Storage starts in the mother plant itself when it attains physiological maturity. After harvesting the seeds are either stored in warehouses or in transit or in retail shops. During the old age days, the farmers used to save seeds in little quantities, but introduction of high-yielding varieties and hybrids and modernisation of agriculture necessitated the development of storage techniques to preserve the seeds.

The main purpose of traditional seed storage is to secure the supply of good-quality seed for a planting programme whenever needed. If sowing time follows immediately after seed collection and processing, seeds can go directly from the processing unit to the nursery, and storage is not needed. This is, however, rarely the case. In seasonal climates with a relatively short planting season, sowing time is normally determined by the wish to have plantable size seedlings at the beginning of the planting season. Hence, seeds must often be stored during the period from harvest to sowing, that is, short-term storage of less than a year.

Many species produce seed (or good seed crops) at long intervals, ranging from a few years to many years. To assure seed supply during the period between two good seed crops, a seed stock should be established (Wang 1975). Even where fruiting is regular and abundant every year, it may be more cost efficient to collect surplus seed to cover several years’ supply rather than to undertake collection every year.

Hence, a seed store serves as a buffer between demand and production and has a regular turnover. Seeds are stored during periods of seed availability and shipped to nurseries or other recipients when required to raise plants. A new type of seed store has arisen during the last few decades, viz. stores for conservation of genetic resources. In these so-called gene banks, seeds (and sometimes other propagation material) are stored for long periods at very low moisture content and temperature (cryopreservation). The techniques applied for storage at ultralow temperatures are quite different from conventional seed storage.

The biochemistry and molecular biology of loss in seed viability during seed storage was investigated in various crops, and many indicators as biomarkers were developed to estimate the viability status of seeds during seed storage. Membrane degradation was shown to be the earliest event to occur during seed deterioration. Membrane reorganisation is slower or may be prevented as a consequence of ageing and death, and perturbations in energy synthesis pathways and respiration which are vital to a viable seed are shown to be associated with early events during seed deterioration. All biochemical pathways require enzymes to catalyse reactions within cell, and their degradation appears a major cause for loss of viability during seed storage. Studies suggest that the first changes in seed deterioration occur at the DNA/RNA level leading to poor cell replication and impaired translation. Identification of changes in storage protein profiles, isozymes and protein nativity through electrophoresis application are considered as best markers for estimating the quality and viability of a seed lot. At molecular level, loss in DNA integrity, DNA fragmentation and downregulation of vigour-related genes were identified as suitable indicators for quality checking.

19.9.1 Stages of Seed Storage

The seeds are considered to be in storage from the moment they reach physiological maturity until they germinate or until they are thrown away because they are dead or otherwise worthless. The entire storage period can be conveniently divided into the following stages: storage on plants (physiological maturity until harvest), harvest, until processed and stored in a warehouse, in storage (warehouses), in transit (railway wagons, trucks, carts, railway sheds, etc.), in retail stores and on the user’s farm.

19.9.2 Classification of Seed Storage Behaviour

A large variation in storability is encountered between species. In seed handling terminology, seeds have traditionally been grouped into two main groups according to their physiological storage potential, viz. recalcitrant and orthodox seed (Roberts 1973). Orthodox seed encompasses seed that can be dried to low (2–5 %) moisture content and can, with low moisture content, be stored at low temperature. Viability is prolonged in a predictable manner by such moisture reduction and reduction in storage temperature. Seeds of recalcitrant species maintain high moisture content at maturity (often >30–50 %) and are sensitive to desiccation below 12–30 %, depending on species. They have a short storage potential and rapidly lose viability under any kind of storage conditions.

Although the terms ‘orthodox’ and ‘recalcitrant’ are relatively well established, storage physiology of seeds seems to cover a more or less continuous spectrum, ranging from extremely recalcitrant, which lose viability in few days, to extremely orthodox, the viability of which under optimal conditions counts in decades or centuries (Farent et al. 1988). Recalcitrant seeds vary with regard to temperature; tropical recalcitrant seeds are normally sensitive to low temperature, whereas temperate recalcitrant seeds can be stored at temperatures slightly above freezing. Recalcitrant seeds vary with regard to temperature; tropical recalcitrant seeds are normally sensitive to low temperature, whereas temperate recalcitrant seeds can be stored at temperatures slightly above freezing. This climatic distinction is, however, not always valid. For example, in Kenya recalcitrant species of Cordia and Vitex tolerate storage temperatures of +2 °C (Schaefer 1991). A group of species which can be dried to a moisture content low enough to qualify as orthodox but are sensitive to low temperatures typical for orthodox seeds has recently been termed ‘intermediate’ (Ellis et al. 1990). An example of such a species is Swietenia macrophylla. Further transition groups within the main classes, sometimes termed sub-orthodox and sub-recalcitrant, demonstrate the continuum in the range of storage behaviour. For example, orthodox seeds generally respond to reduced moisture content with extended viability (within the normal range of moisture content) with an approximately doubled storage life for every 1 % reduction of moisture content (Harrington 1972). That holds for moisture reduction down to 4–5 %, depending on species. Further desiccation does not increase storability, but the seeds are generally not adversely affected by lower moisture content as long as they are humified before imbibition. However, some orthodox species do not tolerate moisture content below a certain minimum, regardless of storage temperature.

19.9.3 Factors Affecting Seed Storage

The period seeds will remain viable in store, their longevity as determined by their genetic and physiological storage potential and by any deteriorating events or damage prior to or during storage, as well as by the interaction between individual factors.

19.9.3.1 Genetic Factors

The seed storage potential is influenced by the genetic make-up of the seed. Storage potential is heritable. Species and sometimes genera typically show inherited storage behaviour, which may be either orthodox or recalcitrant. Accordingly, each species is likely to respond identically to a given set of storage conditions (Bonner et al. 1994). Large genetic variation may, however, occur within species, sometimes ranging from orthodox to recalcitrant, more often expressed as different longevities of seeds from different provenances, individuals or clones when stored under similar conditions. Genetic variation within species may occur on different levels, e.g. land races, provenances, individuals and clones.

Genetic influence on storability may be directly related to progressive ageing, or it may be indirect, ascribed to different susceptibility to factors, which may ultimately lead to loss of viability. For example, inherited variation in seed-coat morphology may cause variation in susceptibility to physical damage during processing, which in turn may influence storability.

19.9.3.2 Initial Seed Quality

Seed lots with high initial viability also have a higher longevity in storage than seed with low initial viability. Seeds of high initial viability are much more resistant to unfavourable storage environmental conditions than low viable seed. Once seed starts to deteriorate, it proceeds rapidly. The seed which is injured mechanically suffered a lot and loses its viability and vigour very quickly. Generally small seeds escape injury, whereas large seeds are more likely to be extensively damaged (e.g. bean, lima bean and soybean). Spherical seeds usually give more protection than flat or irregularly shaped seeds.

The progression of natural ageing with resultant loss of viability is not linear over time but typically follows a sigmoid pattern. Loss of viability is initially slow, followed by a period of rapid decline. The higher the viability when the seed lot enters into storage, the longer the seed will keep viable under a given storage environment. For example, a seed lot with an initial viability of 100 % may take several years to lose 50 % of its viability in storage, while the same seed lot having deteriorated during a few weeks of suboptimal conditions to say 80 % may reach 50 % viability in much shorter time. The different rate of loss of viability during the storage period emphasises the importance of storage at the best conditions available as soon as possible after collection. That becomes especially important for species that rapidly lose viability at, e.g. ambient temperature but respond greatly to improved (e.g. cold) storage conditions.

19.9.3.3 Seed Moisture Content

The amount of moisture in the seeds is the most important factor influencing seed viability during storage. Generally if the seed moisture content increases, storage life decreases. If seeds are kept at high moisture content, the losses could be very rapid due to mould growth. Very low moisture content below 4 % may also damage seeds due to extreme desiccation or cause hard seededness in some crops. Since the life of a seed largely revolves around its moisture content, it is necessary to dry seeds to safe moisture contents. The safe moisture content however depends upon storage length, type of storage structure and kind/variety of seed type of packing material used. For cereals in ordinary storage conditions for 12–18 months, seed drying up to 10 % moisture content appears quite satisfactory. However, for storage in sealed containers, drying up to 5–8 % moisture content depending upon particular kind may be necessary.

19.9.3.4 Relative Humidity

Relative humidity is the amount of H2O present in the air at a given temperature in proportion to its maximum water holding capacity. Relative humidity and temperature are the most important factors determining the storage life of seeds. Seeds attain specific and characteristic moisture content when subjected to given levels of atmospheric humidities. This characteristic moisture content is called equilibrium moisture content. Equilibrium moisture content for a particular kind of seed at a given relative humidity tends to increase as temperature decreases. Thus the maintenance of seed moisture content during storage is a function of relative humidity and to a lesser extent of temperature. At equilibrium moisture content, there is no net gain or loss in seed moisture content.

19.9.3.5 Temperature

Temperature also plays an important role in life of seed. Insects and moulds increase as temperature increases. The higher the moisture content of the seeds, the more they are adversely affected by temperature. Decreasing temperature and seed moisture is an effective means of maintaining seed quality in storage. The following thumb rules by Harrington are useful measures for assessing the effect of moisture and temperature on seed storage. These rules are as follows:

  1. 1.

    For every decrease of 1 % seed moisture content, the life of the seed doubles. This rule is applicable between moisture content of 5–14 %.

  2. 2.

    For every decrease of 5 °C in storage temperature, the life of the seed doubles. This rule applies between 0 and 50 °C.

  3. 3.

    Good seed storage is achieved when the percentage of relative humidity in storage environment and the storage temperature in degrees Fahrenheit add up to 100, but the contribution from temperature should not exceed 50 °F.

19.9.3.6 Microflora and Insects

Loss of viability during storage can be caused instantly by insect or fungal attack or by progressive natural deterioration (ageing). Any of these events are influenced by the storage environment. Temperature and humidity are the most important factors in seed storage. Nondormant seeds may germinate if their moisture content is above 30 %. Rapid deterioration by microorganisms can occur if moisture content is 18–30 %, and seeds with moisture content above 18–20 % respire and metabolise actively. Metabolising seeds may be damaged by accumulation of toxic metabolites or heat if improperly ventilated. Certain seed insects are active at a moisture content of less than 10 %, and damage by fungi may occur down to 4–5 % (Bewley and Black 1994).

19.9.4 Types of Storage

19.9.4.1 Storage at Ambient Temperature and Humidity

Seeds can be stored in piles, single layers, sacks or open containers, under shelter against rain, well ventilated and protected from rodents, and store at least for several months.

19.9.4.2 Dry Storage with Control of Moisture Content but Not Temperature

Orthodox seeds will retain viability longer when dried to low moisture content (4–8 %) and then stored in a sealed container or in a room in which humidity is controlled than when stored in equilibrium with ambient air humidity. Cool condition is especially favourable.

19.9.4.3 Dry Storage with Control of Both Moisture Content and Temperature

This is recommended for many orthodox species which have periodicity of seeding but which are planted annually in large-scale afforestation projects. A combination of 4–8 % moisture content and 0–5 °C temperature will maintain viability for 5 years or more.

19.9.4.4 Dry Storage for Long-Term Gene Conservation

Long-term conservation for orthodox agricultural seeds is −18 °C temperature and 5 ± 1 % moisture content.

19.9.4.5 Moist Storage Without Control of Moisture Content and Temperature

Suitable for storage of recalcitrant seeds, for a few months over winter. Seeds may be stored in heaps on the ground, in shallow pits, in well-drained soils or in layers in well-ventilated sheds, often covered or mixed with leaves, moist sand, peat or other porous materials. The aim is to maintain moist and cool conditions, with good aeration to avoid overheating which may result from the relatively high rates of respiration associated with moist storage. This may be accomplished by regular turning of the heaps.

19.9.4.6 Moist Cold Storage, with Control of Temperature

This method implies controlled low temperature just above freezing or, less commonly, just below freezing. Moisture can be controlled within approximate limits by adding moist media, e.g. sand, peat or a mixture of both to the seed, in proportions of one part media to 1 part seed by volume, and remoistening periodically or more accurately by controlling the relative humidity of the store. This method is much applicable to temperate recalcitrant genera.

19.9.4.7 Cryopreservation

It is also called as cryogenic storage. Seeds are placed in liquid nitrogen at −196 °C. Seeds are actually placed into the gaseous phase of the liquid nitrogen for easy handling and safety. Metabolic reactions come to a virtual standstill at the temperature of liquid nitrogen, and the cells will remain in an unaltered state until the tissues are removed from the liquid nitrogen and defrosted. Therefore, little detrimental physiological activity takes place at these temperatures, which prolongs the storage life of seeds. It is not practical for commercial seed storage, but is useful to store the valuable germplasm.

19.10 Seed Quality Enhancement

19.10.1 Seed Priming

Priming is a pre-sowing treatment that involves exposure of seeds to a low external water potential that limits hydration (controlled hydration of seed) to a level that permits pre-germinative metabolic activity to proceed, but prevents actual emergence of the radical. This will ensure better field emergence and disease resistance under various adverse conditions. The purpose of priming is to reduce the germination time and improve stand and percentage germination under adverse environmental conditions. Primed seeds are used immediately, but may be dried and stored for short time for later use. Basic objective of seed priming is to ensure rapid seed germination and faster growth and to achieve successful and uniform stand establishment in the field. A seed priming treatment can be pre-sowing or prestorage (or mid-storage) treatment. Many priming methods are in practice for seed quality enhancement (Bhanuprakash et al. 2010).

19.10.1.1 Methods of Priming

19.10.1.1.1 Hydro-priming

This technique implies soaking the seeds in water for about specific duration. This terminology is currently used both in the sense of steeping (imbibition in water for a short period) and in the sense of ‘continuous or staged addition of a limited amount of water’. Hydro-priming methods have practical advantages of minimal waste material produced when compared to osmo- and matrix priming.

19.10.1.1.2 Hydro-priming: ‘Steeping’

This is one of the simplest methods and it is being practised over many centuries. On-farm steeping was advocated in many parts of the world as a pragmatic, low-cost/low-risk method for improved crop establishment. Steeping can also remove residual amounts of water-soluble germination inhibitors from seed coats. It can also be used to infiltrate crop protection chemicals for the control of deep-seated seed-borne diseases. This type of seed treatment usually involves immersion or percolation (up to 30 °C for several h), followed by draining and drying back to near original moisture content. Short ‘hot-water steeps’ (thermotherapy), typically <50 °C for 10–30 min, are used to disinfect or eradicate certain seed-borne fungal, bacterial or viral pathogens. However, extreme care and precision are needed to avoid loss of seed quality.

19.10.1.1.3 Halo- and Osmo-priming

In halo-priming, seeds will be soaked in various solutions of inorganic salts such as KCl, KNO3, CaCl2, Ca (No3)2, KH2PO4, etc. This method is practised for higher germination and plant emergence in salt-affected soils. In the case of osmo-priming, substances like polyethylene glycol (PEG), sugars, glycerol, sorbitol, mannitol, etc., are used as osmotic solutes to develop lower water potential. As this process, unlike hydro-priming, regulates water movement in much controlled fashion for longer period, this method is preferred in those crops where soaking in treatment solutions, even for shorter period, leads to germination (e.g. onion, beans, etc.).

19.10.1.1.4 Matrix Priming

Solid matrix priming is done using solid carriers with low matrix potentials, e.g. vermiculite, peat moss, sand, celite, etc., for slow imbibition process. In this case, seeds slowly imbibe and reach an equilibrium hydration level. After priming, the moist matrix material is removed by sieving or screening or may be partially incorporated into a coating. This process mimics the natural uptake of water by the seed from soil. Seeds are generally mixed into carrier at matric potentials from −0.4 to −1.5 MPa at 15–20 °C for 1–14 days.

19.10.1.1.5 Thermo-priming

It is a kind of pre-soaking seed treatment with high and low temperature to improve germination and emergence under different environmental (low- and high-temperature) conditions. This process enables seeds to germinate at temperatures lower or higher than those at which they would haven’t been able to germinate if untreated.

19.10.1.1.6 Bio-priming

Treating the seed with some of microbial agents like Rhizobium, Azospirillum, Pseudomonas aureofaciens, Bacillus, Trichoderma, Gliocladium, etc., is practised in this method for improving seed viability or vigour. Beneficial microbes are included in the priming process, either as a technique for colonising seeds or to control pathogen proliferation during priming. Compatibility with existing crop protection seed treatments and other biological need to be looked into while practising this method. Costs of registration and other factors currently limit the commercial use of bio-priming. Bio-priming as seed treatment that integrates the biological and physiological aspects of disease control was recently used as alternative method for controlling many seed and soil-borne pathogens.

19.10.1.1.7 Drum Priming

Seeds are hydrated in a tumbling drum using a precise volume of water. The amount of water is limited so that it is less than the amount needed for natural imbibition and seed germination to occur. In this method, the seeds are evenly and slowly hydrated to a predetermined moisture content (typically <25–30 % fresh weight basis) by misting, condensation or dribbling. Drum priming enhances seed performance without the loss of additional materials associated with the conventional osmotic priming technique.

19.10.1.1.8 Priming Using Growth Regulators

In this method, seeds are primed using solutions containing minute quantities of plant growth regulators like gibberellic acid, indole acetic acid, benzyl adenine, methyl jasmonate, 1-aminocyclopropane-1-carboxylic acid, etc. This method is usually followed to address seed dormancy problems or to enhance seed germination under adverse soil conditions or to reactivate impaired metabolism of aged and deteriorated seeds. Soaking papaya seeds in GA3 250 ppm enhanced seedling emergence even at low-temperature conditions (Bhanuprakash et al. 2010).

19.10.1.1.9 Seedling Dipping

In this method, a suspension was prepared by mixing culture in desired quantity of water. Seedlings will be dipped in the suspension for 15–20 min and transplanted immediately. Generally 1:10 ratio of inoculant and water will be considered. Dipping in nutrient solutions (starter solutions/formulations) is also practised in this method for healthy and vigorous seedlings.

19.10.1.1.10 On-Farm Seed Priming

Farmers can prime their own seed if they know the safe limits. These safe limits are calculated for each variety so that germination will not continue once seeds are removed from the water. Primed seed will only germinate if it takes up additional moisture from the soil after sowing. It is important to note this distinction between priming and pre-germination – sowing pre-germinated seed under dry land conditions can be disastrous. In most cases seed can be primed overnight and is simply surface-dried and sown the same day. Occasionally, sowing may be unavoidably delayed – by heavy rain, for example. If primed seed is surface-dried and kept dry, it can be stored for several days and then sown as usual, and this still performs better than non-primed seed. Farmers can prime their own seeds if they know the maximum length of time for which their seeds can be soaked before seed or seedling damage occurs. After the seeds have been soaked for the appropriate length of time, the water is drained off and the seeds are surface-dried by placing them on a cloth or plastic sheet on the ground for 15–30 min or, for small amounts of seeds, rolled gently in a dry cloth so that they do not stick together (Harris 2006).

19.10.1.2 Advantages of Seed Priming

  1. 1.

    Increases germination rate

  2. 2.

    Early and uniform emergence

  3. 3.

    Germination under broader environment (drought and high salt)

  4. 4.

    Improves performance of low-vigour seeds

  5. 5.

    Improves vigour of immature seeds

  6. 6.

    Breaks seed dormancy

  7. 7.

    Permits germination in suboptimal temperature

  8. 8.

    Reverses seed deterioration effect

  9. 9.

    Increases enzyme activity, protein content and ATP level

  10. 10.

    Synchronisation in flowering among hybrid and parental lines

The beneficial effect of priming is associated with an increase in respiration activity as well as increase in synthesis of proteins and of RNA and DNA. Synthesis of new proteins related to vigour, germ-related proteins, LEA proteins, β-tubulin expression, HSP synthesis and disappearance and expression genes related to vigour are noticed in relation to quality enhancement through seed priming.

19.10.2 Seed Pelleting

Seed pelleting is the mechanism of applying needed materials in such a way that they influence the seed or soil and the seed-soil interface. The main objective was to build small irregularly shaped seeds into spheres facilitating precision drilling in order to achieve optimum plant stand and thereby reduce the need for gap filling. Seed pelleting also serves as a mechanism of applying needed materials in such a way that they affect the seed or soil at the seed-soil interface. The three basic steps involved in pelleting are stated as stamping, coating and rolling. First in the sequence fungicide is to be directly coated on to the seed to improve its efficiency followed by filler materials before coating the nutrients. It is essentially required to avoid direct contact of nutrient chemicals to the seed. Otherwise this may result in scorching of the seed and developing seedlings, as final sequence seeds can be coated with filler materials followed by bioinoculant and biofertilisers (Table 19.1).

Table 19.1 Types of seed pelleting and its constituents
Full size table

19.10.3 Seed Colouring

The practice of providing an exogenous colour coating to seed is only of recent interest. But it is very much prevalent in developed countries for the last decade. Modern seed technology provides a wide selection of enhancements that can be aimed to translate varieties of genetic potential into improved harvest yield and quality. Colouring of seeds along with pelleting/film coating is adapted in private sector seed companies in the USA, Canada and Europe; these enable the seeds to be sown in defined pattern besides modifying germination. Seeds of many cultivated crops have naturally irregular proportions and surfaces and wide size ranges and are sticky or very small. These features can make it hard to handle and efficiently sow the seed. So seed colouring helps in sealing the cracks on the seed coat, and it will improve the physical appearance of seeds. However, it gives the seed a distinct and attractive look to reduce dust and promote environment safety as well as worker safety in the field. Hence, ‘pelleting’, ‘colouring’ and coating (Table 19.2) are a family of treatments that are used to make seeds sown easily by altering their shape, weight and textures besides modifying its germination.

Table 19.2 Methods of seed coating technologies
Full size table

19.11 Synthetic Seed Technology

The successful demonstration of encapsulation of tissue culture-derived propagules in a nutrient gel has initiated a new line of research on synthetic seeds. Synthetic seed can be defined as the artificial encapsulation of somatic embryo, shoot buds or aggregates of cell or any tissues which has the ability to form a plant in in vitro or ex vivo condition. Synthetic seeds can be stored for a long time in appropriate condition.

Recently, production of synthetic seeds by encapsulating somatic embryos has been reported in few species. One prerequisite for the application of synthetic seed technology in micropropagation is the production of high-quality, vigorous somatic embryos that can produce plants with frequencies comparable to natural seeds. Inability to recover such embryos is often a major limitation in the development of synthetic seeds. Synthetic seed technology requires the inexpensive production of large numbers of high-quality somatic embryos with synchronous maturation. The overall quality of the somatic embryos is critical for achieving high conversion frequencies. Encapsulation and coating systems, though important for delivery of somatic embryos, are not the limiting factors for development of synthetic seeds.

19.11.1 Types of Synthetic Seeds

Desiccated Synthetic Seeds

Desiccated synthetic seeds are produced from somatic embryos either naked or encapsulated in polyoxyethylene glycol. This type of synthetic seeds is produced in desiccation-tolerant species of plant.

Hydrated Synthetic Seeds

Hydrated synthetic seeds are produced by encapsulating the somatic embryos in hydrogels like sodium alginate, potassium alginate, carrageenan, sodium pectate or sodium alginate with gelatin. Alginate hydrogel is frequently selected as a matrix for synthetic seed because of its moderate viscosity and low spinnability of solution, low toxicity for somatic embryos and quick gelation, low cost and biocompatibility characteristics.

19.11.2 Importance of Synthetic/Artificial Seeds

The artificial seeds can be used for specific purposes, notably multiplication of non-seed-producing plants and ornamental hybrids (currently propagated by cuttings) or the propagation of polyploid plants with elite traits. The artificial seed system can also be employed in the propagation of male or female sterile plants for hybrid seed production. Cryopreserved artificial seeds may also be used for germplasm preservation, particularly in recalcitrant species (such as mango, cocoa and coconut), as these seeds will not undergo desiccation. Furthermore, transgenic plants, which require separate growth facilities to maintain original genotypes, may also be preserved using somatic embryos. Somatic embryogenesis is a potential tool in the genetic engineering of plants. Potentially, a single gene can be inserted into a somatic cell. In plants that are regenerated by somatic embryos from a single transgenic cell, the progeny will not be chimeric. Multiplication of elite plants selected in plant breeding programmes via somatic embryos avoids the genetic recombination and therefore does not warrant continued selection inherent in conventional plant breeding, saving considerable amount of time and other resources. Artificial seeds produced in tissue culture are free of pathogens. Thus, another advantage is the transport of pathogen-free propagules across the international borders avoiding bulk transportation of plants, quarantine and spread of diseases.

19.11.3 Advantages of Synthetic Seeds

  1. 1.

    Easy propagation of hybrid plants.

  2. 2.

    Easy propagation of genetically modified crops.

  3. 3.

    Easy propagation of endangered species.

  4. 4.

    Elite genotype can be preserved and propagated using synthetic seeds.

19.11.4 Uses of Synthetic Seeds

  1. 1.

    Synthetic seed production is cost effective.

  2. 2.

    Genetical uniformity is maintained by using synthetic seed technology.

  3. 3.

    Synthetic seeds are small; therefore, they are easy to handle and transport.

  4. 4.

    Provides protection against pest and diseases.

19.11.5 Limitations of Synthetic Seeds

  1. 1.

    Limited production of viable micropropagules in synthetic seed production and asynchronous development of somatic embryos

  2. 2.

    Improper maturation of somatic embryos that makes them inefficient for germination and conversion into normal plants

  3. 3.

    Lack of dormancy and stress tolerance in somatic embryos that limit storage of synthetic seeds

  4. 4.

    Poor conversion of even apparently normally matured somatic embryos and other micropropagules into plantlets