Journal of the Andaman Science Association Vol.

20(1):26-33 (2015)
ISSN 0970-4183, Printed in India
© Andaman Science Association, Port Blair (A & N Islands), India

SEED ENHANCEMENT THROUGH PRIMING, COATING AND PELLETING

ABSTRACT
Quality seed plays seminal role in augmenting agricultural productivity as well as production. Only by using quality
seeds, productivity can be enhanced to the tune of 15-20% easily and under optimum management the increment may
touch upon up to 45% depending upon the crops since the efficiency and efficacy of all other inputs in the production
technology gamut are contingent upon the quality of seeds being used. Since antiquity the importance of quality seed
to enhance agricultural productivity is well evident as mentioned in old testimonials, literatures, scriptures, treatises,
epics, and many other ancient documents. In course of time through critical observation and elaborate experimentations
conducted over years across continents, it was observed that there are several ways and means to enhance vigour of
germinating seedlings while emerging from the seed, which produce a uniform crop stand and finally substantially
more yield is achieved by adopting simple techniques. Amongst a couple of such techniques, seed priming is a
unique one, through which invigouration of germinating seedlings may be achieved either by adoption of hydro
priming, osmo-priming etc. There are ample evidences that using specific chemicals/organics and soaking the seeds
in diverse treatments have achieved invigoration in many crops. Similarly by coating seeds with diverse materials
like insecticides, nutrient coating etc., uniform seed germination and development of uniform crop stand have been
demonstrated in many crops, which finally display enhanced productivity coupled with good seed quality attributes.
Pelleting, an another magnificent technique, is normally used in case of irregular shaped seed or for extremely small
seeds so as to achieve uniform shape, which makes sowing efficient and uniform. Nowadays, nanoparticles are being
used to obtain invigoration in respect of diverse characters especially in dispensing nutrients directly to germinating
embryos or in halting seed borne pathogen incidence by clogging the pores in the cell membrane for achieving higher
productivity owing to healthy crops. The present review has mainly been focused on retrospecting and prospecting the
major seed enhancement techniques and the success stories in two major life line cereals crops- rice and wheat in India
precisely, which is deemed to be useful to the readers to explore the possibility of using such prospective emerging
technologies on large–scale to enhance productivity through value addition in nutshell.

Keywords:Rice, Wheat, Quality Seeds, Priming, Coating and Pelleting.

Seed quality is the major decisive factor governing commodityindia.com). Seed enhancement may be defined
stand establishment of any crop and thus bears immense as post-harvest treatments that improve germination and
importance and bears utmost priority in case of high seedling growth or facilitate the delivery of seeds and other
value, low volume crops like vegetables in particular and inputs/materials required at the time of sowing smoothly.
for high volume low value crops in general for enhanced Seed enhancement technology predominantly possess a
productivity and production as well. A number of diverse central objective to further improve seed performance
materials/ treatments at varying doses have been used to by treating with specific additives/chemical/organics/
increase the rate and uniformity of seedling emergence in botanicals etc under very specific regimes and with the
wheat and rice, which are generally categorized for seed aid of certain planting equipments to grow uniform crop
enhancement, which is a kind of value addition (www. obviously to harness higher productivity and production

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(Halmer, 2006). Various techniques have been employed emergence under broader range of environments that led
to assure superior performance of additives in different to improved seedling vigour and growth. The objective
crops and most have been found to have immense of seed hydration technology is principally aimed at
commercial application (TeKrony, 2006). This includes increasing the percentage and rate of germination,
three general areas of enhancement: pre sowing hydration expand the range of temperature regime over which the
treatment (priming), coating, pelleting technologies and seed will germinate and increase the uniformity of stand
seed conditioning. Seed priming first allows the seed to establishment in the field. Three general approaches for
imbibe moisture, using various protocols of osmo-halo hydration have been developed: prehydration, priming
and osmo-hydro-priming, followed by redrying the seeds and solid priming. Lastly, priming has been commercially
to undertake routine handling smoothly in most efficient used to eliminate or greatly reduce the amount of seed
manner. This process controls hydration of seeds to a borne fungi load and bacteria such as Xanthomonas
campestris in Brassica seeds and Septoria in celery
level that allows pre germination activities aggressively
have been shown to be eliminated within seed lots after
in a regulated manner. Seed hydration is a process in
priming. Upon completion of priming, the seeds are dried
which seeds are hydrated using various protocols also
back to enable normal handling safe, storage and planting.
and subsequently redried to permit routine handling. This
Primed seeds can be stored successfully for short periods
process results in increased germination, uniform seedling
without losing the benefits gained from the treatment.

Fig.1: Diagrammatic representation of sequential coating involving diverse

In seed priming seeds are partially hydrated until the (Bray et al. 1989), build up of germination enhancing
germination process begins, but radical emergence does metabolites (Basra et al. 2005), osmotic adjustment
not occur (Bradford, 1986). Priming allows the metabolic (Bradford, 1986), and for seeds that are not redried after
processes necessary for germination to occur without true treatment, a simple reduction is discernible in imbibations
germination. Primed seeds actually exhibit increased lag time (Bradford, 1986). Other scientists have written
germination rate, enhanced germination uniformity and excellent reviews on seed priming (Sivasubramaniam et
enhanced speed of emergence and at times, greater total al. 2011). Our review aims primarily to sum up earlier
germination percentage (Basra et al. 2005; Shehzad et al. works on rice seed priming in particular. Osmo
2012). Increased germination rate and uniformity have conditioning or osmo priming is the term used to describe
been attributed to metabolic repair during imbibition the soaking of seeds in aerated, low water potential

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solutions. In this special type of seed priming, polyethylene Lee & Kim (2000) investigated the effects of osmo-
glycol (PEG) or salt solution is used to control water conditioning on germination of normal and naturally aged
uptake and prevent radicle protrusion (Bray, 1995). PEG seeds by analyzing total sugar content and α-amylase
is most commonly used because of its nontoxic nature and activity. The normal seeds had a higher total sugar content
large molecule size, which lower water potential without and α-amylase activity than the aged seeds. Aged seeds
penetrating into the seeds. The salts used to lower water those underwent osmo-conditioning and hardening
potential are KNO3, KCl, K3PO4, KH2PO4, MgSO4, CaCl2, increased their total sugar and α-amylase activity. The
NaCl and mannitol. Salts supply the seed with N and latter was found positively correlated with total sugar and
other nutrients essential for protein synthesis during seed germination rate. Basra et al. (2005) had the same results
germination. Those salts, however, result in occasional when they evaluated the effects of osmo-conditioning
toxicity, a disadvantage to the germinating seedlings. (-1.1 MPa KNO3 for 24 and 48 h), traditional soaking, and
Seed soaking, sometimes followed by dehydration of toxic effects of KNO3 osmopriming on fine rice. Increased
seeds has been demonstrated to improve subsequent α-amylase activity and sugar content were also reported
germination of numerous vegetable seeds especially in the treated seeds in comparison with the control set.
under suboptimal conditions (Bradford 1986; Muhyaddin The salts used to control water potential may cause
& Weibe, 1989). More recently, osmo conditioning has toxicity and/or germination inhibition in rice (Basra et al.
been introduced successfully in cereals, including rice. 2003, 2005). In both studies, -1.1 MPa KNO3 adversely
Lee et al. (1998a) conducted an experiment to find out the affected the germinating seeds and seedlings. Hardening
optimum water potential, temperature and duration for (Wetting and drying or hydration-dehydration) refers to
rice seed priming. It was concluded that priming in water repeated soaking in water and drying (Basra et al. 2003).
(0MPa) for 4 d at 150C and for 1 d at 250C displayed the The hydration-dehydration cycle may be repeated several
same results, whereas 4 d was found to be the optimum times (Lee & Kim, 2000). The hardening treatment for 24
priming time in 0.6 MPa PEG solution, regardless of h proved to be better for vigour enhancement (Basra et al.
priming temperature. The same authors investigated the 2005) than osmopriming (-1.1 MPa KNO3) for 24 and 48
effects of priming on early emergence of rice seeds under h and traditional soaking (overnight soaking followed by
soil moisture conditions. Rice seeds were primed by keeping in saturated gunny bags up to radicle appearance).
soaking in a -0.6MPa PEG solution at 250C for 4 d. Basra et al. (2003) also evaluated the effects of seed
Germination and emergence rates and time from planting hardening for 24 and 18h and reported that this resulted in
to 50% germination (T50) of primed seeds were found less better invigouration of hardened seeds of fine rice in
than those of untreated seeds by 0.9 - 3.7 d. Lee et al comparison to osmo-conditioning and the control set.
(1998c) suggested priming of rice seeds to ensure better Greater α-amylase activity and higher sugar content were
seedling establishment under adverse soil conditions. In a also reported in the hardened seeds than in the control.
greenhouse trial, osmopriming (CaCl2, and CaCl2 + NaCl) Farooq et al. (2005) introduced a new technique for rice
improved seedling vigour index and seedling stand seed invigoration, integrating both seed hardening and
establishment in flooded soil (Ruan et al. 2002). Compared osmo-conditioning. Seeds of course and fine rice were
with CaCl2 + NaCl priming solution, the addition of GA3 hardened in various salt solutions rather than in tap or
to CaCl2 + NaCl did not increase significantly the speed of distilled water. Osmo hardening in CaCl2 (with an osmotic
emergence or stand establishment (Ruan et al. 2002). Du potential of -1.5 MPa) solution was found to be better
& Tuong (2002) concluded that, when rice is seeded in than with other salts and simple hardening (Farooq et al.
very dry soil (near the wilting point), priming further 2005). Humidification is a pre sowing hydration treatment
increases plant density (especially with 14% KCl solution in which seeds are equilibrated under conditions of high
and saturated CaHPO4 solution), tiller number, and grain humidity (Lee et al. 1998b). Humidification of normal
yield. In drought-prone areas, seed priming reduced the rice seeds with high germination rate did not increase the
need for a high seedling rate, although it can be detrimental germination rate, but could accelerate the germination
if seedling is done in soil that remains at or near saturation. rate of aged seeds, especially those kept under
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unfavourable soil conditions and suboptimal temperatures emergence and vigorous seedlings achieved by soaking
(Lee et al 1998a, c). Lee et al. (1998b) investigated the seeds in water for some time followed by surface drying
effects of humidification on normal and aged rice seeds. before sowing, which may result in higher crop yield
Relative humidity (RH) and humidification duration were (Harris et al. 2000). This soaking practice is termed on-
found not to effect germination rate, but reduced the time farm seed priming- a simple, cheap and low risk method
to 50% germination of normal seeds, but at 80% RH of promoting rapid seedling establishment and vigorous
found to reduce germination percentage and increased the early growth. The duration of soaking is critical and
time to 50% germination. Incorporating plant growth should be less than the safe limit of each crop cultivar.
regulators as part of presoaking, priming, and other pre- The safe limit is defined as the maximum length of time
sowing treatments of many crops resulted in improved that farmers should prime seeds; if exceeded; this can
seed performance (Miyoshi & Sato, 1997). GA3 is well result in seed or seedling damage brought about by
known to act upon α-amylase or the breakdown of starch premature germination (Harris et al. 2000). Primed seeds
stored in the seed that is used by the growing embryos will not continue to germinate, unless those are placed in
during germination. GA3 and ethylene stimulate the a moist soil environment. If primed seeds are sown on to
elongation of the mesocotyl, coleoptile, and internodes of a seedbed within adequate moisture, those will not
rice seedlings after germination. Abscisic acid, on the germinate unless moisture subsequently becomes
other hand, promotes elongation of the mesocotyl of rice available (e.g. rainfall). In contrast, seeds soaked longer
seedlings (Lee et al. 1999). Miyoshi & Sato (1997) than the safe limit will continue to germinate even in the
observed effects of kinetin and gibberellins on dehusked absence of an external moisture source. The use of pre
seeds of indica and japonica rice to study their effects on germinated seed possess inherent risk, whereas the use of
germination under aerobic and anaerobic conditions. primed seed has an advantage-the primed seed behaves as
Under anaerobic conditions, the responses of dehusked dry seed if sowing is delayed or seed bed conditions are
indica and japonica rice seeds to kinetin and gibberellins made suboptimal. Soaking overnight was also successful
differed- response to kinetin was found to be negative in rice and proved to be highly cost-effective, resulting in
while response to gibberellins was strongly positive. better crop stand, earlier maturity and higher yields at
Under aerobic conditions, the stimulatory effects of little cost (Harris et al. 2002). The same study noted that
kinetin on the germination of dehusked seeds were found primed rice seed uniformly and vigorously germinated
greater than those of gibberellins. Dry heat treatment of and emerged faster (1-3 d), leading to a wide range of
seeds is done for two reasons: (1) to control external and phenological and yield-rated benefits. In direct-seeded
internal seed borne pathogens, including fungi, bacteria, rice, on-farm seed priming resulted in better emergence
viruses and nematodes and (2) to break seed dormancy (91% vs. 61%), earlier flowering (71 vs. 74.7 d), taller
(Schmidt, 2007). Generally, the high temperature in the plants (108 vs. 94 cm), and longer panicles (22.4 vs. 20.3
treatment reduces seed viability and seedling vigour, but cm), and more panicles per plant (5.7 vs. 7.9). Traditionally,
the optimum temperature for breaking dormancy promotes rice seedlings are widely transplanted in nurseries, thereby
seed germination and seedling emergence in rice (Lee et increases production cost and water requirements. The
al. 2002). Farooq et al. (2004) exposed coarse and fine rising labour cost and the emerging water crisis are the
rice seeds to dry heat treatment- 400C for 72 h and 600C major challenges being faced by the rice-producing world,
for 24 h and chilling (-190C) treatment for 72 h. In fine including India, Bangladesh, Pakistan and all other south
rice dry heat treatment at 400C for 72 h resulted in and south-east Asian countries and recently emerged
decreased T50 and increased radicle and plumule length, nontraditional rice growing areas in USA and Australia in
root length, root/shoot ratio, root fresh and dry weight, particular. Direct seedling could be an alternative, but
radicle and plumule growth rate and shoot fresh weight. poor germination, uneven crop stand, and high weed
In coarse rice, none of the treatments improved infestation are serious constraints that prevent the
germination and seedling vigour. Recent research on a adoption of direct-seeded rice (Du & Tuong, 2002).
range of crop species showed faster germination, early Effective herbicides are currently available for weed

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Mandal et al. J. Andaman Sci. Assoc. 20 (1):2015

control, but poor germination and poor crop establishment 1986; Muhyaddin & Weibe, 1989; ncof.dacnet.nic.in).
remain a serious concern. Seed priming bears immense The need for research in this area is more strongly felt
the potential to overcome this problem since invigouration now than in the past for enhanced productivity at the
persists under less optimum conditions such as salinity interface of shrinking land under rice cultivation day by
and excessively high and low temperature (Bradford day.
Fig.2: Rice upgradation by egg flotation technique

Source:
http://agritech.tnau.ac.in

Vigour of treated seeds are assessed based on test is selected random and kept for oven drying overnight
germination percentage, seedling length and seedling dry at 900C temperature (ISTA, 1999). The dried seedlings are
weight. weighted and the values are multiplied with germination
percentage for calculating the vigour index.
Vigour index I = Seedling length X germination %
Vigour index II = Germination % X seedling dry weight For knowing speed of germination, 50 seeds in
two replicates are subjected to standard germination
The seedling length is measured on linear scales,
test (ISTA, 1999) and normal seedling are counted and
which are randomly selected from the standard
removed daily until no further germination is observed.
germination test. For determination of the seedling dry
The rate of germination is calculated as mean germination
weight, seedling from each replicate of the germination
time (MGT).

MGT = ∑fx / ∑X
Where, f = number of days from the beginning of the germination test.
X = number of seeds newly germinated seedling on each day.

Coating is a sophisticated process of applying are used with active ingredients such as insecticides
involving precise amount of active ingredients along with and fungicides (Johnson, 2008), which improve the
a liquid material directly on to the seed surface without resistance of the seed towards pest and diseases in the
obscuring its shape. Coating has gained popularity as a much-warranted juvenile stage, besides improve the
seed-coating method over the last several years because seedling vigour (Elzein et al. 2006). Seed coating with
of worker safety considerations. It is a process of applying commercial polymers diluted with nutrient instead of
useful materials to form a continuous layer of thin coating water may sow increased seed germination (Farooq et al.
over the seed without altering the shape or size, by 2012). Encapsulation of plant protectants by film coating
employing water as the solvent. Seed coating polymers ensures a uniformity of application superior to slurry
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application, the other method. Once plant protectants are directly to the seed can be “carried” in the seed pellet.
sealed to the seeds, dispersal to the environment prior to The act of applying a plant protectant in a band within
planting is minimized. All the dosage originally applied the pellet is known as “pellet loading”. The pellet either
to the seed will be available against the pests in the target acts to “dilute” the negative impact of a plant protectants
environment, and worker exposure to harmful dusts is as it moves through the pellet to the seed, or acts as a
minimized (Jiang et al. 2008). barrier to prevent direct seed contact. Active products
can thus be “loaded” onto the seed while minimizing
Pelleting is the process of enclosing the seed with
adverse seed germination effects (Harveson et al. 2007).
small quantity of ingredient along with filter materials
The total amount of “toxicants” applied per acre is less
is coated to produce a globular unit of standard size
with in-furrow or other soil applications. In nutshell it is
to facilitate precision planting. Seed pelleting is the
concluded that with deployment of very simple priming,
process of enclosing a seed inside a small quantity of
coating and pelleting techniques enhanced productivity as
inert material just large enough to produce a globular
well production is a feasible proposition in diverse crops
unit of standard size to facilitate planting. Small and
which is deemed to be spearheading in future to augment
irregularly shaped seed can now be treated as larger and
Indian as well as global agriculture.
round-shaped. Simulation of seed in the field is therefore
easier. There are two components to a seed pellet: bulking
ACKNOWLEDGEMENT
coating) material and binder. The bulking material can
be either being a mixture of several different mineral The authors like to thank profusely the technical
and/or organic substances or a single component. The and supporting staff attached with the plant physiology
coating material is the “work-horse” of the duet. The laboratory for their extensive help in executing this piece
coating material changes the size, shape and weight of of work.
the seed. Desirable characteristics of a good coating
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