What is seed?
In fact what is true seed
? Why true seed or botanical seed because there are other types of seed materials are also there which are used for regeneration of that particular plant. So that type of seed material can be called as Agricultural seed those which are in different form like bulb, rhizome, corm, nut, runner, stolon etc. and etc. But the true seed can be defined as it is the fertilized mature ovule which consist of an embryonic plant or miniature plant otherwise called as Embryo which is the only living part of a seed, it also consists of either Endosperm / Perisperm/ Cotyledon which is the stored food material that can help the growth and development of the seedling during early seedling establishment days and it encapsulated by a protective structure generally called as Seed Coat. So these are the basic structural arrangements so far as true seed is concern.
Seed Quality can be defined as Possession of seed with required genetic and physical purity that is accompanied with physiological soundness and health status. Means the quality attributes of a seed like physical quality, genetic purity, physiological quality and seed health are responsible for assessment of the quality of the seed. Quality seed should have high genetic purity, high pure seed percentage/ physical purity, high germinability, high seed vigour or stamina of the seed, high field establishment means ability of a seedling to establish or grow well to be established as a healthy plant, free from pest and disease attack, having good shape, size, colour accordance with the specification of the variety, then high longevity of the seed means shelf life or storability what can be, optimum moisture content for storage means for long term storage it should be 6-8% and for short term storage it can be up to 10-13% and congregating the all it should have high market value.
Seed quality enhancement
means the application of physical, physiological, biological and chemical agents to the seed in order to enhance the physical, physiological,
genetical, biochemical and health qualities of seed. Seed enhancement technologies are gaining increasing attention for their potential to confer greater disease resistance in seeds, improve seed vigor and modify seed emergence capabilities.
Why Seed Quality Improvement/ Enhancement:
For any crop, the time from sowing to seedling establishment is crucial, because at that time the seeds are exposed to wide range of environmental stresses like the fluctuating temperature and moisture of the environment, monsoon failure or gambling of monsoon, sometimes severe drought, effect of harmful micro-organisms, destruction of the seed by seed, soil and air borne pathogens, damage by insects, cold, frost, problem soils, competition from weeds and toxic effects of chemicals present in soil, which cause problems of dormancy, create hindrance in germination of seed and survival of the seedling. So, the Value addition to the seed is very much necessary to tolerate prolonged exposure to adverse environment during imbibition
and seedling establishment so as to improve the crop stand ( Imbibition means Absorption of water or moisture which is irreversible that can be imbibed by the seed which helps during germination process). So A judicious and comprehensive package of crop-specific seed management technologies starting from the dormancy breaking treatments, seed germination and vigour augmenting treatments, seed protection treatments, and finally seed handling and conditioning treatments need to be developed for sustainable good crop growth and productivity. Seed enhancements include physical, physiological, chemical, and biological treatments to overcome germination constraints for uniform plant stands, earlier crop development, and better yields. So the rate of germination and seedling vigor is improved due to reduced emergence time by the earlier start of metabolic activities of hydrolytic enzymes and resource mobilization which starts before the germination process initiates. Nutrient management, ion uptake, hormonal regulation, activation of the antioxidant defense system, reduced lipid peroxidation and accumulation of compatible solutes are some mechanisms conferring biotic and abiotic stress tolerance in plants. In this plot, there is a need to minimize the factors associated with reduced vigor during seed production,
improve seed storage and handling, develop high-tech seeds by seed industry at appropriate rates and integrate agronomic, physiological, and molecular seed research aspects for the effective regulation of high-quality seed.
TYPES OF SEED QUALITY ENHANCEMENT
Improvement in seed quality is attempted through various seed treatments and they can be divided in to three major groups like
a. Pre-sowing seed treatments
b. Pre-storage seed treatments
c. Mid-storage seed treatments
Pre-sowing seed treatments means the treatment of seed or method or technique employed for enhancement of seed quality is done before the sowing of the seed in field to obtain highest qualitative output from a seed. This stage is very much useful to obtain the qualitative part of the seed. Second type is Pre-storage seed treatments
means after harvesting of the seed it can be treated well before storage or taking in to godown for improving so also maintaining the quality aspect during the storage period which enable the seed for better storability and longevity. Likewise the third category is Mid-storage seed treatments which is done during the storage period to maintain the seed quality so as to enhance the longevity.
a. Presowing treatment includes 3 methods like
i. Dormancy breaking treatments,
ii. Germination augmenting treatments and
iii. Seed coating treatments.
i. Dormancy: Dormancy means resting phase of seed at that time the metabolic activity inside the seed remain stopped or occurred in a very slow or negligible rate. Or Dormancy can be defined as inability of seed to germinate in a favourable condition. Means the physiological activities occurring inside the seed create hindrance to emerge the radicle and plumule from the seed. So, breaking of dormancy is needed to enable the process of germination. And to improve the germination different types of germination augmenting treatments can be done. Seed coating treatment can be done before the sowing of the seed for precision seed sowing or planting of very small sized seed and to protect the seeds from birds, squirrels by cheating them with seed colouring treatments. These are some methods of presowing treatments.
After that we can undertake the Halogenation
, antioxidant, seed sanitation and seed fumigation before taking the seed to store in storage bin or godowns to enhance the shelf life and storability of the seed.
As like above alternate hydration-dehydration technique can be used as mid storage treatment during the storage period to enhance the storability or longevity of the stored seed.
So to break the dormancy i.e. either exogenous dormancy means dormancy of the seed or dormancy caused due to external factors and endogenous dormancy i.e. dormancy due to internal factors can be broken by following or adopting any of the listed method or their combination.
A. Soaking in water
B. Mechanical scarification
C. Acid scarification
E. Warm stratification
F. Cold stratification
G. Temperature treatments
H. Wetting and thawing
I. Alternate wetting and drying
J. Scorching / Burning
K. Electrical seed treatment
L. Seed treatment with growth stimulants
A. Soaking in water
It refers to soaking of seeds in cold or hot water for a period ranging from few hours to several days. It is used to break physical or chemical dormancy. In the case of cold water soaking, seeds are soaked in cold water for one to three days; but once in 12h water should be changed to avoid fermentation bcz if we put the seed in a container of water for longer period it can be fermented by the activities of microorganism. In the case hot water treatments, seeds should be soaked in boiled water, just removed from the heat source for one to 80 minutes. Physical dormancy caused by hard seed coat is overcome by softening of the seed coat by soaking the seed in water. Chemical dormancy caused by presence of inhibitors is overcome by leaching of the inhibitors during long soaking period. The seeds can be soaked in running water for a day to leach out the inhibitors eg., coumarin in coriander; hydrocyanic acid in sunflower.
B. Mechanical scarification
Mechanical scarification means rubbing or aberration of seeds against hard surface. It is done to partially damage the hard seed coat over the seed in order to soften the seed coat. During the scarification, the seed coat is aberrated thereby the hard seed coat is made permeable to water uptake or absorption or imbibition.
C. Acid scarification
It is the process of treating the seeds in sulphuric acid for a pre-standardized duration. It is standardised depending upon the type of seed. It is done to overcome physical dormancy caused by hard seed coat. It is done by soaking the seeds in commercial grade sulphuric acid for a pre-standardized duration with often stiffing and washing the seeds for 5-10 minutes to remove all traces of acid. Shade dry the seeds.
is subjecting the seeds to pretreatment by making use of animals and microorganisms as an important factor in the breakdown of seed coat impermeability.
Animals: Acacia nilotica pods are fed to penned sheep or goats and the seeds are collected from the droppings. The combination of moisture, warmth and chemical action of the digestive juices softens the hard seed coat and the rough surface of their stomach also acts as a scarifying object and the seed becomes permeable.
Insects: Termites are an important agent for breaking down seed coat dormancy to many parts of tropics as it feeds and removes the exocarp of the seed. eg.Terminalta.
Exposing imbibed seeds to higher temperatures for a period of time is named as stratification. It is done to overcome mechanical and morphological dormancy. Soak the seeds in hot water at approximately 40- 45°C for 48h. Store at a warm temperature. Periods of treatment vary from 2 weeks to 16 weeks depending on species.
F. Cold Stratification:
Incubate the seed at a low temperature of 0- 5°C over a moisture substratum for 23 days to several months. It depends on the nature of the seed and kind of dormancy.
G. Temperature Treatments:
Plant which grow in temperate and cooler climates require a period of chilling for breaking of dormancy. Likewise high temperature of 40- 45°C treatemnts are exhibited on early flowering winter annuals.
H.Wetting and thawing
means the process of ice, snow or another frozen substances becoming liquid or soft as a result of warming up.
I. Then alternate wetting and drying
J. Then scorching and burning or fire treatment for extremely hard seeds can be used.
K. Electrical seed treatment using electromagnetic field,
L. Seed treatment with growth stimulant or growth hormone can be done for dormancy breaking.
ii. Germination augmenting treatments
A. Seed fortification
B. Dry permeation
C. Seed hardening
D. Seed priming
F. Magnetic seed treatment
G. Seed treatment with bioinoculants
H. Pre-germinative sprouting
I. Seed infusion
J. Seed invigouration
A. Seed fortification
is the process of enriching the seeds with bioactive chemicals for improving the germination and seedling vigour. To the known volume of seeds, one third volume of the nutrient solution is added and allowed to imbibe for short duration. The imbibed seeds should be dried under shade. It also improves the seed storability
. The main objective is to achieve high vigour seed to overcome unfavourable soil reactions. Seed fortification with MnSO4 @ 0.5 to 1% will improve oxidative-reduction potential of seeds, which ultimately leads to higher germination.
B. Dry permeation means Soaking of seeds in organic solvents like acetone, petroleum ether and dichloromethane containing desired hormonal and non-hormonal chemicals for 2- 3h followed by evaporation of the solvent in air. It is an approach to improve the germinability and vigour of seed by infusion of bioactive chemicals into the seed without altering seed moisture content.
C. Seed hardening is the process of hydrating the seed to initiate the pre-germinative metabolism followed by dehydration which fixes the biochemical events is called as seed hardening. It is done in order to impart resistance against stress conditions viz., drought and cold, to the emerging seedlings. Seeds are allowed to take up a certain amount of water, and then they are kept moist at 10, 25°C for several hours before drying in a steam of air. The best results can gain in two to three cycles of wetting and drying, although for some one cycle is sufficient. Different quantities of water are recommended for different species and cultivars of seed or grain.
D. Seed priming is the process of controlled hydration of seeds to a level that permits pre-germinative metabolic activity to proceed, but that prevents actual emergence of the radicle. Seeds are soaked in variety of solutes, including solutions of various inorganic salts, sugars and polyethylene glycol (PEG), a chemically inert, high molecular weight compound does not penetrate the cell walls. The
temperature suggested during priming is between 10-15°C. The duration of priming varies with the crop.
Heydecker et al. (1973) used different terms depending upon the methods adopted for priming.
Hydropriming- Soaking the seeds in water
Osmopriming – Soaking the seeds in osmotic solutions
Halopriming – Soaking the seeds in salt solutions
Biopriming – Soaking the seeds with biological agents like Pseudomonas, Trichoderma and liquid biofertilizers
Solid matric priming- a method of priming by which the seeds are mixed with solid material and water in known proportions
: Pre-sowing irradiation of the seeds is a novel measure to increase the yield potential by improving germination and vigour. Air dried seeds are irradiated by using experimental gamma units. The unit consists of a definite configuration of irradiator such as a hollow cylinder or a linear or flat irradiator and maintaining an accurate time exposure for conducting the experiment. In the process of the growth and development of plants raised from irradiated seeds, beginning from seedling emergence and ending with the ripening, there appears new, quite diverse changes manifested in the acceleration of the cell division rate, enhancement of growth and development, change of organogenesis
, yield increase and its quality change i.e. there emerges a very complicated sequence of changes which have been termed as the effect of distant irradiation action.
F. Magnetic seed treatment: This simple treatment involves exposure of seeds to a magnetic field to improve germination and vigour for specified duration. Magnetically treated seeds respire slowly, but register higher respiration quotient values with increased enzyme activity viz., a-amylase and nitrate reductase.
G. Seed treatment with bioinoculants/Biological treatment: Seeds can be treated with Trichoderma viridae (or) Pseudomonas fluoreseens @ 4 / kg of seed for the control of root rot infection and other seed borne diseases.
H. Pre-germinative sprouting/ Pre-germination of seeds: Seeds are soaked in water for a specific time and incubated in moist gunnies for 12-16h where the seeds start its germination by protrusion of the radicle. This technique is widely used for paddy, groundnut and gourds. The pre-germination should strictly be restricted to the slight visual observation on the radicle by breaking the seed coat; otherwise the treatment will result in adverse effect.
I. Seed infusion: Seed infusion is a method of impregnation of seeds with bioactive chemicals/ organic solvents such as acetone or dichloromethane instead of water. The organic solvents slowly increase the infusion of chemicals into seed. The organic chemicals are evaporative in nature. Hence, drying back to the original moisture content is not necessary. This technique helps to avoid the damage caused to the seed due to water soaking. Hence, this method is highly suitable to seeds that suffer with soaking/seed coat injury. Simultaneously, it also provides protective, regulatory and selective functions of the chemicals to improve the performance of seed with the help of organic solvents.
J. Seed invigouration/ seed enhancements are preharvest treatments to improve germination and seedling growth or to facilitate the delivery of seeds and other materials required at the time of sowing.
iii. Seed Coating Treatment
A. Seed pelleting
B. Seed coating/ Film Coating (Hydrophilic & Hydrophobic)
C. Seed Colouring
D. Fluid drilling/ Gel Seeding
E. Seed Protection Treatments
F. Bio-fertilizer treatment
A. Seed pelleting was developed in the 1940’s. When the seeds are very small in their size and shape than the original purpose was to build up individual or groups of small, irregularly shaped seeds into spherical capsules that would ensure precision planting (Helmer, 1988). It is used for a large number of vegetable seed species. The process of enclosing the seed inside a small quantity of inert material just large enough to produce a globular unit of standard size is termed as seed pelleting. Seeds are introduced into a coating drum or pan that resembles a cement mixer. An amalgam of pelleting materials (clays, limestone, calcium carbonate, vermiculite) and cementing adhesives (gum arable, gelatin, methylcellulose, polyvinyl alcohol, polyoxyethylene glycol-based waxes) used to form the pellet and other compounds such as innoculants, fungicides, etc. may be added to enhance seed performance. As drum rotates, the seeds to first sprayed with water followed by the addition of the pelleting materials with binder. The wet seed attracts and becomes coated with the dry pelleting material and the pellet gradually increases in size with each turn of coating drum. Longer rotation times with greater amounts of pelleting materials lead to create pellet size and roundness. At the end of the pelleting process, a binder is added to harden the outer layer of the pellet. The ingredients of the seed pellets exert respective positive influence on seed performance eg. diammonium phosphate stimulates prolific root growth. Rice seed pelleted with calcicum peroxide to increase oxygen availability in submerged paddy conditions can be obtained in Japan (Helmer, 1988).
B. Seed coating/ film coating: This coating technique uses polymer binders with firm-forming abilities to treat seeds. These products may be obtained from specialist suppliers and are co-formulated with coloranto and plasticizers to improve coverage (Helmer, 1994). Film coating has become a standard method for applying fungicide and other chemicals to vegetable sods (Ester, 1994). Field crops including maize, oilseeds, rapeseed and sunflowers are now being treated with film coatings and there is much interest in its application to these crops. Particularly attractive features of this technology include reduced dust-off of chemicals uniform coverage of pellets for some vegetable and sugar beets seeds. Potential for use of film coatings as moisture barriers for seeds stored at high humidity was demonstrated by McGee et al. (1988) in that a polyvinylidene chloride copolymer emulsion applied to maize and soybean seeds effectively controlled storage fungi invasion during storage for three months at 85% relative humidity and 25oC by reducing the rate of uptake of moisture by the seeds. It is a process of applying useful materials to form a continuous layer of this coating over seed without altering the shape or site. The advantage of film coating over other coating process is the absence of dusting off problem and improvement of seed flow in planting equipment. The application of seed coating is very similar to the slurry seed treatment and similar equipment is used, wherein the seeds are sprayed or dipped in the dissolved additives and immediately dried. Film coating involves application of additives dissolved in a dyed solution of a sticky polymer and immediately dried.
Types of film coating
Hydrophilic coating: Coating with a hydrophilic polymer can reduce rate of water uptake, lower solute leakage and improve emergence of seed. It is suitable for sowing in wet soils.
Hydrophobic coating: Starch graft polymers and magnesium carbonate are capable of improving movement of air and water. The increase in germination is due to fact that the fine particles in the coating act as “wick” or moisture attracting material or perhaps to improved seed soil contact. It is suitable for sowing in dry soils.
C. Seed colouring: Colouring of seeds using natural or artificial dyes. It is done to
to prevent inadvertent use of treated seeds for food or feed purposes to identify the seeds eg. A line, B line, R line etc., to project their seed in the market eg. Private companies The seeds are sprayed or dipped in the dissolved dyes
D. Fluid drilling or gel seeding: Seed priming is used to complete the early phases of germination in aerated water in controlled environment before seeds are planted in the field. One version of this is fluid drilling by which seeds are mixed in a liquid gel and planted in the field. Both chemical and biological control agents may be delivered by this technique. Metalaxyl, etridiazole and captan applied by fluid drilling controlled Pythium damping-off tomatoes (Taylor and Harman, 1990). It is mixing of pre-germinated seed in a viscous gel, which is sown with an appropriate droll to maintain the seed moisture of the pm-geminated seeds and to prevent injury to emerged radical. Seeds are germinated in aerated water until radicle emergence and then they are mixed in a VISCOUS gel eg., alginate gel. The viscous gel provides a cushion to the emerged radicle thus preventing any mechanical damage during drilling. The gel also gives a protective covering to the seed against any moisture loss.
E. Seed protection treatments: They are the treatments that use beneficial microorganisms to offer the potential for sustained plant growth. It can serve two purposes viz., seed protection and nutrient supplementation. Seeds are mixed with adhering agents such as rice gruel, and coating with the specific biological strains in appropriate proportions followed by surface drying. Seed dressing: It refers to the application of pesticides (fungicides, insecticides or a combination of both) to seeds before sowing in order to protect the seeds and young seedlings from soil borne pathogens. Seeds are thoroughly mixed with required quantities of chemicals eg. Thiram and captan 2 g/kg of seeds or botanicals eg. leaf powder of Azadirachto indica and Vitex negundo.
F. Biofertilizer treatments:
Seeds can be treated with biofertilizers like Rhizobium, Azospirillum and Phosphobacteria 200 g / ac, which will enrich nitrogen to the plan. Biofertilizer
treatment should be done after fungicidal treatment.
b. PRE STORAGE SEED TREATMENTS
The treatments given to the seeds prior to or during storage to protect the seed from deteriorative changes and from pest and diseases are called pm storage treatments. The types of pre storage seed treatments are :
B. Antioxidant treatment
C. Seed sanitation
D. Seed fumigation
it is a chemical reaction that involves the addition of one or more halogen to a compound or material. Halogen materials means 5 chemically related elements like fluorine, chlorine, bromine, iodine and astatine. Artificially created element Tennessine also a halogen.
Dry dressing: It is the application of halogens like chlorine, bromine and iodine to seeds before storage as dry dusting to stabilize the lipoprotein biomembrane. Calcium carbonate, fresh chalk, talc charcoal or activated clay are first exposed to vapours of halogens and alcohols @ 2-5g/kg seed. An alternative method is to add the chemicals directly to the carrier (50 — 500mg of chemical added tot-5g carrier for treating lkg seed) in a closed container. Calcium carbonate has proved to be a good carrier. After equilibrating the carrier-chemical mix, the seed is thoroughly dressed with the same and kept for 24-72h in the closed container and thereafter stored in the usual way. Bleaching powder (Calcium oxy chloride) may be directly mixed with the seed at the rate of 1-4 g/kg seed.
Vapour treatment: Exposure of seeds to halogen vapour in a closed container for 16-72h, to very low concentrations of halogens. The concentration of chemicals and the time of exposure would depend on the material concerned. Halogens like chlorine, bromine and iodine or alcohols, such as ethanol, methanol or impropanol are used. The halogens are obtained by adding lml of sulphuric acid to 50mg of KCI, KBr or KI in a small petri-dish placed in the bottom of a glass desiccator (of 5.5 litre capacity) in which seeds are kept on the porcelain plate for the required duration of exposure. Chlorine may also be obtained by just placing bleaching powder calcium oxychloride 2.5g which would slowly release chlorine and iodine by putting 2550mg solid iodine crystal in the petri-dish. The process of lipid peroxidation is initiated by a free radical, which attacks the neighbouring unsaturated fatty acid to form lipid free radicals. This is a continuous process which results in (i) loss of membrane integrity, (ii) co-oxidation of associated cellular components and (iii) production of cytotoxic aldehydes. This results in loss of viability and vigour. The role of the halogen is stabilization of double bonds of unsaturated fatty acid of lipoprotein biomembranes to prevent the process of lipid peroxidation. The possible termination is by stabilization of polyunsaturated fatty acid (PUPA) by a halogen. Besides, halogens also act as free radical controlling agents
B. Antioxidant treatment:
Application of antioxidants such as vitamin A, C, E, butylated hydroxytoluene (BHT) to seeds before storage as wet or dry treatments which delay the physiological ageing. The seeds are applied with antioxidants through soaking in respective solutions at particular concentration. Antioxidants such as vitamin A, C and E provides hydrogen atom for quenching the lipid radical thereby putting an end to free radical propagation and subsequent damage to cell membrane and ultra-cellular structures.
C. Seed sanitation:
The seed sanitation treatments refers to the application of pesticides (fungicides, insecticides or a combination of both) to seeds to disinfest and disinfect them from various seed borne and soil borne pathogenic organisms and storage insect pests to safe guard the seed and seedlings against the seed and soil borne pathogens. Seed borne pests and diseases may be carried within seeds or on seeds or they may accompany the seed as free living organisms or in debris.
The seeds are simply dipped or soaked in the chemical solutions and the fungicides applied as dust, slurry or liquid in recommended concentrations.
a. Seed disinfection: This refers to the eradication of fungal spores that have become established within the seed coat or in more deep seated tissues. For effective control, the fungicidal treatment must actually penetrate the seed in order to kill the fungus that is present.
b. Seed disinfestation: This refers to the destruction of surface borne organisms that have contaminated the seed surface, but have not infected the seed surface.
c. Seed protection:
Seed protection is the application of a chemical to protect seed from disease organisms in the soil. A systemic fungicide seed protectant
also may provide post emergence protection to the crop, usually from foliage diseases, for several weeks after plant emergence.
D. Seed fumigation:
It is a process of exposing the seeds to fumigants (gaseous form of chemical) to control seed borne fungi and insects, which cause seed deterioration during storage. The seeds should be brought to equilibrium moisture content at 60% RH, and then they should be enclosed in air tight containers and fumigated at temperature of 27±1.5°C for required durations. After fumigation, seeds placed in cloth bap are aerated for 21 weeks under room condition. Subsequent second and third fumigations are repeated after 3 and 6 months after first fumigation. Examples of fumigants are ethylene oxide, aluminium phosphide, calcium cyanide, ethylene dichloride and carbon tetrachloride, ethylene dibromide, carbon disulphide or hydrogen phosphide.
The toxic effects on the fumigants bring about the control of fungi or insects. The fumigant can penetrate into the seeds to control the deep-seated pathogens. Before going for fumigation, a thorough knowledge of seed moisture level and type of infestation, choice of fumigant, its doses and exposure time and necessity of number of fumigation are very essential.
c. MID STORAGE SEED TREATMENTS
Seeds in storage accumulate damage to cell membranes during senescence means with passing days seed is deteriorated due to its metabolic activities. Mid storage seed treatments are capable of reducing the age induced damages and restoring the seed vigour by controlling free radical reactions and consequent peroxidative damage to lipoprotein cell membranes. Besides, the seed viability and productivity of stored seeds are also improved.
Hydration – Dehydration: It is the process of soaking the low and medium vigour seeds in water with or without added chemicals usually for short durations to raise the seed moisture content to 25-30% and drying back the seeds to safe limits for dry storage.
Types of H-D treatments: The wet treatments include soaking-drying, dipping-drying, spraying-drying, moisture equilibration soaking-drying and moist sand conditioning-drying. The choice of the treatment depends upon the characteristics of seed and initial vigour status of the seeds.
a. Soaking – Drying (S-D): Stored seed is soaked in water or solution of chemicals sufficient to cover it and kept at room temperature for 2-6 hours depending on the material with occasional stirring. The soaked seed is taken out and after surface drying in the shade for some time, dried back to the original moisture content. Dilute solution of chemicals such as sodium or potassium phosphate (di and mono basic), sodium chloride, p-hydroxy benzoic acid, p-amino benzoic acid, oxalic acid and potassium iodide can also be used at 10-‘ to 104 M concentrations. Fungicidal and insecticidal formulations can also be incorporated in the soak water.
b. Dipping – Drying (D-D): Seeds are dipped in water or solutions of the aforesaid chemicals for only 2-5 minutes and the wet seed is taken out immediately and kept covered for 2-6 hours depending on the material, for absorption of surface water followed by drying back in S.D. This treatment is effective in most high and high-medium vigour seeds of rice, wheat and jute, summer and winter vegetables
c. Spraying – Drying: Seeds are spread in a thin layer and then an amount of water (approximately 1/5 to 1/4 of the seed weight) is sprayed on to it in two equal installments (turning over the seed layer after the first spray) and then kept covered by a polythene sheet for 2-4 hours before drying back. This treatment is similar to D-D in its efficacy and suitability.
d. Moisture equilibration – Drying (ME – D): Here, the seeds are placed in thin layers on trays kept on a raised platform in a closed moisture saturated chamber lined internally with moist blotters giving nearly 100% RH at room temperature. After 24-48 hours, depending on the material and
ambient temperature, the seed is dried back in the usual way.. For soaking injury prone seeds, this treatment gives a slow and progressive rise in moisture content. ME-D, however, difficult to practice on a large .ale and is not advocated for low vigour non leguminous seeds because of possible aging effect of the treatment especially when given for prolonged periods.
e. Moist sand conditioning – Drying (MSC-D):
This treatment is similar to the moisture equilibration
treatment, but easier to practice. For slow and progressive moisture uptake, the seed is thoroughly mixed with pre-moistened sand, using 3 times the amount of air dry sand than seed. Moisture content of sand is adjusted to 5.10 by adding the required amount of water or solution of chemicals to previously washed and dried fine grain building grade sand. The addition of water should be to be adjusted as to get the required hydration effect without initiating the germination. After mixing the dry seed with the premoistened sand, the mixture is kept at room temperature for 16-36 hours depending on the material and sand moisture content. The seed absorbs moisture from sand and after incubation the hydrated seed is separated from sand by sieving and dried back to the original weight.
Hydration and dehydration treatment should be given only to stored seeds. It is effective in low and medium vigour non- leguminous seeds. The moisture equilibration and moist sand conditioning treatments in which moisture is taken up by the seed in a slow and progressive manner, are recommended for relatively high vigour seeds and seeds of pulses and leguminous vegetable crops. Direct soaking of leguminous seeds should be avoided. It would not make a seed germinable, which has already lost viability.