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Seed Production Guide
Prepared by B.R. Ntare
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Contents
Technical Aspects of Groundnut Seed Production .............................................. 1
1. Introduction ....................................................................................................... 1
2. Site selection .................................................................................................... 1
2.1 Soil selection .........................................................................................................1
2.2 Climatic conditions ...............................................................................................1
2.3 Field isolation ........................................................................................................2
2.4 Rotation .................................................................................................................2
2.5 Soil preparation .....................................................................................................2
2.6 Sowing ...................................................................................................................3
2.7 Fertilization ............................................................................................................4
2.8 Crop maintenance ................................................................................................4
2.9 Irrigation .................................................................................................................5
2.10 Phytosanitary protection ........................................................................................5
2.11 Harvesting/Digging ...............................................................................................9
Post-harvest technology....................................................................................... 11
1. Introduction..................................................................................................... 112. Handling of the harvested crop ..................................................................... 11
2.1 Curing .................................................................................................................. 11
2.2 Stripping/Winnowing .......................................................................................... 12
3. Seed processing ............................................................................................. 13
3.1 Sieving ................................................................................................................ 13
3.2 Density separator ............................................................................................... 13
3.3 Packaging ........................................................................................................... 14
4. Seed storage and conservation .................................................................... 14
4.1 On-farm storage of pods .................................................................................... 14
4.2 Collective or industrial storage .......................................................................... 15
4.3 Storage of shelled groundnuts .......................................................................... 15
4.4 Some technical aspects of the industrial preparation of ready-to-usegroundnut seeds ................................................................................................ 16
5. Phytosanitary protection of stored seeds ..................................................... 19
5.1 Insect control ...................................................................................................... 20
6. Seed physiology ............................................................................................. 22
6.1 Germination ........................................................................................................ 226.2 Dormancy and methods for breaking dormancy ............................................... 23
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Technical Aspects of Groundnut Seed
Production
1. Introduction
One of the most efficient means for the African farmer to improve the productivity
of his farm is by the use of high quality groundnut seeds. Organizing high quality
seed production and distribution is critical to the implementation of any
development plan. This precondition also applies to other factors that affect
productivity. Pod and grain size of a specific variety is an important parameter
for determining seed value. The crop should be grown under appropriate
conditions of climate and soil fertility to ensure good pod formation, filling, and
seed maturity. Cultivation techniques must be perfectly mastered in order for
the plant to attain its full potential and ensure quality production. These standards
are fundamental for producers who want to sign up for a national multiplication
program. The farmer must also accept controls and conform to production
certification standards.
2. Site selection
Under low rainfall conditions, seeds should be produced in the most suitable
areas in order to maximize potential production. This also minimizes transport
and marketing costs.
2.1 Soil selection
Groundnuts prefer light soils that facilitate penetration of the gynophores (pegs)
after pollination, and easy digging without pod loss. Groundnuts required well
drained sandy loams and must not be sown in shallow soils exposed to erosion.
Groundnut plants are sensitive to salinity, a little sensitive to alkaline soils but
they prefer soil with a neutral pH. High soil acidity (pH
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as drought resistant with performances that make it one of the main crops
cultivated in dry tropical areas. However, good performance is strongly linked
to adequate soil water content at sowing time, followed by well-distributed
rainfall. The life cycle of the groundnut can be divided into four phases thatcorrespond to variable water requirements. For a 90-day variety grown under
conditions in the Sahel, the requirements are as follows:
vegetative growth (0-20d): 3.5 mm/d;
flowering (21-40d): 5.2 mm/d;
pod formation and filling (41-70d): 4.4 mm/d;
maturation (71-90d): 3.9 mm/d.
Early small-seeded groundnut varieties require 300-500 mm of rainfall and late
large seeded-varieties 1000-1200 mm.
2.3 Field isolation
Groundnuts are self-pollinating and therefore do not require isolation. Different
varieties must be placed 5-10 m apart to avoid mixing during harvesting and
stripping.
2.4 Rotation
Groundnut is very sensitive to the preceding crop and must not be cultivated for
several consecutive years. A well-adapted rotation program could improve the
efficiency of fertilizer use, soil structure, weed and volunteer plant control, and
reduce pest pressure. Nematodes and certain foliar diseases transmitted by soil-
borne pathogens can be partially controlled with an appropriate rotation program.
2.5 Soil preparation
In semiarid regions, removal of crop residues that spread diseases and harbor
pests is a priority activity. For light soils, this type of cleaning followed by a
shallow raking is often done after the first light rains. This eliminates early weeds
and breaks up the soil surface where seeds are sown soon after the first substantial
rainfall. In wetter areas or with heavier soils, fields must be ploughed at the
beginning of the cycle to suppress weeds and break up the soil, which must then
be refined by harrowing. With this soil type, raised-beds are often made to limit
run-off or plant asphyxia by standing water. The beds can be wide and flattened
at the top in order to accommodate two rows per bed.
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1 Insecticide2 Fongicide
2.6 Sowing
Before sowing, seeds must be carefully prepared. The preparation depends on
the way they were stored. When stored in shell, groundnuts must be preferably
hand-shelled and sorted in order to eliminate skinned, immature, moldy, andsmall seeds. Seeds are then treated with an insecticide/fungicide mixture to protect
them against insects and fungi during germination. The most common are:
carbofuran1 , heptachlor1, captafol2 , thiram2, benomyl2, captan2, carbendazim2,
etc., depending on the regulations of the country where they are used.
Planting date is linked to rainfall distribution in the area and the length of the
variety growth cycle. Soil moisture must be sufficient to guarantee good
germination. Seeds must not be sown immediately after heavy rains since theyimbibe too much water, which causes rotting. This also results in excessive soil
compaction, which may hinder germination.
Spacing depends on the growth habit and the variety: 10 to 20 cm between
plants, and 40 to 60 cm between rows. Planting density is also affected by water
availability, and cultivation methods (flat or raised beds, manual or mechanized).
In addition, the spacing must allow plants to cover the soil within 50 days ensuring
better weed control and rational water use. In rain-fed crops, density varies
between 110 000 (Virginia) and 170 000 (Spanish) plants per hectare. This canbe as high as 250 000 plants/ha under irrigated conditions. The weight of seeds
in shell required to sow one hectare is called the seeding rate (SR). This depends
on varietal characteristics, seed quality and planting density. The SR is calculated
as follows:
Density (plants/ha) weight of 100 seeds (g)
10 seed viability (%) shelling yield (%)
With manual sowing, individual seeds are sown 3-5cm deep. Mechanized sowingis widely practiced in Senegal. This is done using a single row planter, generally
drawn by a horse or donkey. In this way, one hectare can be sown in 8 hours. A
disk adapted to the seed size, turns inside of a hopper and regularly dispenses
the seeds into a furrow opened by the planter blade. A weighted rear wheel then
closes the furrow.
SR =
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2.7 Fertilization
A reasonable level of organic matter must be maintained in the light, weakly
structured, tropical soils where groundnuts are grown. The groundnut plant has
an extensive root system that allows it to explore a large volume of soil andtherefore benefit from organic manure residues from preceding crop (cereal).
Groundnuts can be cultivated with an N-P-K type mineral fertilizer. Calcium
must be added to slightly acidic soils to correct the pH and improve the technical
quality of the seeds. Calcium deficiency leads to a high percentage of aborted
seeds (empty pods or pops) and improperly filled pods. Calcium is barely
translocated across the leaves, therefore it must be applied near the fruiting
zone (as a side dressing). This must be done at the beginning of pod formation
in order to be directly absorbed by the pegs and the young developing pods.The quantity of fertilizer needed to maintain a seed-producing field depends on
soil type and varies between 200 to 600 kg/ha of gypsum for large-seeded
varieties.
2.8 Crop maintenance
2.8.1 Hoeing Weeding
Early hoeing affects future crop growth since it allows better infiltration of
rainwater, controls early weeds and therefore prevents competition for water, a
scarce resource in the Sahel. Hoeing facilitates careful removal of volunteer
groundnut plants from previous crops and incorporation of chemical fertilizers
applied after sowing. Hoeing can either be manual or mechanical. The first hoeing
is generally followed by one or two manual weedings. The crop must completely
cover the soil from the 50 to 60 days, thereby limiting weed growth. Chemical
weed control is uncommon, however, application of a pre-emergence herbicide
would result in possible savings in time and labor, which could be better be
spent on other work. This technique also requires specialized equipment as wellas knowledge of chemical products and their application methods.
2.8.2 Culling out off-type plants
This consists of manual removal of plants of other varieties present in the field.
Depending on the degree of contamination, a field can be retained or rejected
for seed production. In Senegal, fields of mother seeds should have less than
one off-type in 1000 and those of certified seeds, one in 200. Applied standards
for varietal purity of groundnut seeds are as follows; a minimum purity of 98%for level 1 seeds, and 95% for level 2 seeds. Regular field checks allow elimination
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of foreign plants based on phenotypic characteristics of the cultivated variety.
Purifying the field maintains the genetic quality and can only be effective if
checks are rigorously continued throughout downstream operations (removal
of foreign pods during shelling, cleaning of equipment, warehouses and packagingmaterial).
2.9 Irrigation
Although groundnut is a rustic plant, high yield seed production can be guaranteed
using irrigation, especially for first generations. Irrigation also allows off-season
(outside of the rainy season) groundnut production, which accelerates seed
multiplication in Sahelian countries. Quality production is ensured using an
irrigation program adapted to crop demand at each developmental stage.Different irrigation methods can be used including overhead (sprinkler, etc.),
drip and furrow irrigation. The latter is the most commonly used in West Africa
but does not always ensure homogenous water distribution, especially in large
fields. Telethermometry is a useful tool for managing irrigation systems. It links
water demand to the temperature of the canopy and facilitates optimum water
supply, and thereby avoids wastage of water resources. Individual or communal
irrigated fields must be privileged partners for seed production since input usage
(fertilizer, lime, phytosanitary protection) recommended for seed production is
rewarded by high yield and quality.
2.10 Phytosanitary protection
Groundnuts are exposed to pest and disease attack that can cause deterioration
of the quality of the product and lead to significant losses. Some of the most
common diseases are as follows:
2.10.1 Foliar diseases
Groundnut rosette is a disease caused by a virus complex (combination of
several viruses) transmitted by an aphid, Aphis craccivora Koch. There are
three forms of the disease: chlorotic, mosaic or green. The green form occurs
mainly in West Africa. Infected plants are stunted and production is greatly
reduced. The disease can be controlled using resistant varieties along with specific
cultural practices (early, high density sowing). Chemical control is often difficult
and not economically feasible.
Peanut Clump Virus (PCV) is a soil and seed borne disease. Continuous culturefavors its development. Infected plants are stunted and have symptoms such as
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mottling, mosaic, and chlorotic rings on the leaves. They must be removed and
contaminated fields must be excluded from any seed multiplication program.
Peanut Mottle Virus (PMV) is a viral disease. Symptoms include dark greenirregular patches on young leaves. These are not easily seen on older leaves but
a fine mottling can be observed with backlighting.
Early and late leaf spot are diseases caused by fungi that commonly occur in
groundnuts. Early leaf spot, Cercospora arachidicola, causes dark brown
necrotic lesions surrounded by a chlorotic halo on the upper leaf surface. Late
leaf spot, Phaeoisariopis personata, causes almost circular necrotic lesions that
are very dark brown. Spores are produced on the leaf under surface. At high
disease incidence, chlorotic infected foliage prematurely senesces and falls.Although chemical control is effective, it is not very profitable since several
treatments are required during the vegetative growth phase of the crop. Farmers
also have to try to control groundnut rust at the same time.
Groundnut rust (Puccinia arachids) is a widespread fungal disease. Orange
pustules appear on the lower leaf surface and necrotic lesions can occur on any
aerial plant part. Unlike leaf spots, rust causes necrotic leaves to dry out but
remain attached to the plant. Crop rotation is recommended in order to limit
infestation, like for leaf spots.
Other foliar diseases can also be observed. These include Sclerothium leaf spot,
andAlternaria wilts.
2.10.2 Soil borne diseases
Aspergillus niger, Aspergillus flavus, Macrophomia phaseolina and
Rhyzoctonia solani are the most common pathogens causing seed rot during
sprouting. Sorting and treating seeds before sowing are the most effective and
economically feasible means of controlling these diseases. IfMacrophomia is
identified as the causal agent, infected groundnut plants must be uprooted and
destroyed.
2.10.3 Soil pests
The most extensive field damaged is caused by millipedes, termites, white grubs
and nematodes.
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Millipedes (Myriapoda) attack young seedlings and developing pods. They cause
significant damage and are difficult to control. Seedling damage can be limited
by incorporating an insecticide into the seed treatment.
Termites (Isoptera)Macrotermes sp.,Microtermes sp. and Odontotermes sp.
are widespread throughout Africa. They can cause extensive damage in the
field, especially under conditions of water stress when they attack plant by
excavating through the central axis of main roots and stems. They equally attack
developing pods, this can be recognized by holes made under the beak of the
pods. Crop damage is most severe just after harvesting. Termites cause extensive
scarring of the pods which makes them brittle. The pods are then perforated and
the seeds eaten. This creates a gateway forAspergillus flavus. Treating seeds
before they are sown controls termites during the first month. However, forproduction of first level seeds, an insecticide like carbofuran (a carbamate) is
recommended at a dosage of 10 kg per hectare around 40 days after planting.
The residual activity of this insecticide ensures control up until the harvest. This
broad-spectrum insecticide also partially controls millipedes and has some effects
on nematodes. At harvest, soil must be dusted with insecticide before groundnuts
are stacked for curing.
White grubs (Coleoptera) Schizonycha spp. are the larvae of small brown
chafers. They are found in the pod development area and feed on roots, nodules
and pods. Damage symptoms include yellowing and rapid wilting of the plant.
These larva attack several plant species, however, groundnut infestation is
fortuitous. Constant monitoring and chemical control must be included in any
on-farm IPM (Integrated Pest Management) strategy.
Nematodes (Scutellonema cavenessi) are found through out the Sahel. The
nematode is a soil dwelling round worm, less than 1 mm long, which bores into
roots and pods. Nematode presence in the roots severely decreases the numberof nodules and the activity of the nitrogen-fixing bacteria. Infected plants have
yellowish foliage and severely reduced production. Pod damage is first
characterized by the appearance of small brown spots. These become larger and
darker as the nematodes grow. This type of damage can be partially controlled
using a systemic insecticide such as carbofuran. Large scale trials conducted in
Senegal showed that average pod yield can be increased by 500 kg/ha using
dibromochloropropane (DBCP) soil treatments after the first rains, which
stimulates nematode activity.
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2.10.4 Foliar insect pests
These can be divided into two groups: piercing-sucking insects and defoliators
(chewing insects), most of which belong to the orders of coleoptera or
lepidoptera.
The groundnut aphid (Homoptera: Aphidiae), Aphis craccivora Koch, is
commonly called the black groundnut aphid. The black adult is 2-3mm long.
Reproduction is always parthenogenic and there are several generations per
year in tropical climates. Development from nymph to adult takes 5-6 days.
These piercing-sucking insects feed on nutrients produced by the plant and
damage can be particularly severe during prolonged periods of drought. Aphids
form numerous colonies on leaf undersurfaces and on young shoots. They canequally be detected by the fungi (sooty moulds) that develop on the honeydew
excreted by aphids. This species is the vector of groundnut rosette virus. Chemical
control with 300 g a.i./ha of dimethoate has been reported to be very effective.
Thrips (Thysanoptera) are small, slender insects, 2 mm long and 0.5 mm wide.
They can be either yellow, brown or black. The wings are fringed and the tarsi
have a vesicle called an arolium that allows them to stick to slippery surfaces.
The most common thrips that attack groundnut in Africa are Scirtothrips dorsalis,
Thrips palmi, Frankliniella schultzei andHeliothrips indicus . Thrips are piercing-sucking insects. They destroy the parenchyma of the plant with their short stylets
and so reduce photosynthetic capacity. Reproduction is often parthenogenic
and they can produce up to 15 generations per year, especially under hot humid
climatic conditions. Apart from the use of resistant varieties, chemical treatment
with 15 g a.i./ha of Deltamethrine (Decis) or with systemic products can be
used to control high infestations.
Leafhoppers (Heteroptera) are tiny insects belonging to the family Cicadellidae-
Jassidae. Several species of the polyphagous genus Empoasca ( E. kerri, E.
fasciallisandE. lybica) are among the most important insect pests of groundnuts
in Senegal. These insects can cause direct damage by removing plant nutrients
from the parenchyma and by injecting toxic enzymes that cause organ
malformation. Egg oviposition into the tissues can also cause wounds with
secondary effects. Most of these species are vectors of viruses or mycoplasmas.
Drought stress increases damage. The main symptoms include leaf rolling near
leaf bases, yellowing of leaflet tips, stunting, shortening and malformation of
the internodes (dwarfism). Chemical treatment with systemic products likedimethoate (200-250g a.i./ha) provides effective control.
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Caterpillars (Lepidoptera: Arctiidae), includeAmsacta moloneyi, commonly
called the hairy cowpea caterpillar a very polyphagous insect that also attacks
groundnuts. The adult is 12-16 mm long with a wingspan of 35-40 mm. The
larva is a hairy defoliating caterpillar with a yellow head and yellowish brown-patterned segments with ochre nipples. Adults appear 3-5 days after the first
substantial rains and lay their eggs on young plants. This species can go through
3 to 4 generations per year. It can be controlled by cultural practices (end of
cycle ploughing, late sowing). Treatment of young larva with insecticides such
as endosulfan (250 g a.i./ha), monochrotophos (300 g a.i./ha) or fenvalerate
(100 g a.i./ha) and biological control with Bacillus thuringiensis are also
recommended.
Groundnuts are attacked by various species of hairy caterpillars in other countries.These all belong to the family Arctiidae and includeAmsacta albistra ,Amsacta
moori andDiacrisia obliqua.
2.11 Harvesting/Digging
Optimal harvesting date is one of the first problem to be solved. Flowering is
indeterminate in the groundnut; there is therefore a variable proportion of mature,
immature and developing pods at the end of the crop cycle. Premature harvesting
of the crop leads to quantitative losses in production, impacts on oil and proteincontent and on seed viability. If the soil is moist, keeping non-dormant varieties
in the field for longer than the average cycle duration causes high level of
germination of mature seeds while still in the pods. This delay exposes pods to
pest attack; increases seed acidity and aflatoxin contamination, which have direct
consequences on depreciation of seed quality. The most pertinent test for
monitoring groundnut maturity is checking the internal parenchyma of the pods.
It must be turgid, smooth, and dry ranging from white to dark brown. Mature
pods are adequately indicated by the presence of several brown spots. Fields
must be sampled from the theoretical date of pod maturity (varietal cycle) by
pooling several plants and analyzing their pod maturity. The crop can be harvested
once there are 70-80% of mature pods. In non-dormant varieties, the crop is
considered to be mature when 2% of the plants have germinated seeds.
Digging consists of cutting the main root below the pod bearing area. Plants are
then dug up and shaken in order to remove soil adhering to the pods. This
operation is generally manual. The main root is cut with a sharp tool, plants are
then manually dug up, shaken and placed into stacks for rapid curing. Theseoperations take an average of 150 hours per hectare but can very easily be
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mechanized. A simple tool, drawn by an animal can be used. It consists of a
triangular blade 20-50 cm wide (depending on the type of cultivation) supported
by a metallic framework with two steering arms, a front wheel and a hook for
the harness. With this equipment, digging is three times faster than by hand.This basic equipment can also be used as a weeding hoe.
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Post-harvest technology
1. Introduction
Seed quality mainly depends on following appropriate handling and storage
techniques for the harvested crop. Handling facilitates the selection of the best
seeds while storage conditions ensure the conservation of high seed quality.
Groundnut seeds are protected by a shell which acts as an excellent natural
barrier protecting the seed from deteriorating agents. However, this shell should
be perfectly intact in order to protect the seed. Removal of damaged pods is
therefore necessary. Crop residues mixed with the pods are often sources of
contamination (insect eggs, larvae and adults, fungal spores, etc.). They also
represent a pointless use of storage capacity and should be removed.
Phytosanitary protection is equally critical to conservation of the overall value
of the seeds.
Seed quality depends on the following compulsory steps:
good quality stored products;
following recommendations for phytosanitary protection and periodic
inspection especially during warehousing;
appropriate fitting of storage facilities.
2. Handling of the harvested crop
Groundnuts lose their seed value at maturity if they are not correctly handled.
Setting up a stock of quality seeds begins with harvest at optimal pod maturity,
good digging conditions (loose soil, appropriate equipment, rapid harvest) and
adequate curing.
2.1 Curing
Pods with 30-40% water content cannot be stored immediately after harvesting
without them overheating. Likewise, handling of newly harvest pods with seeds
still adhering to the hull could provoke irreversible biological damage and partially
alter the seeds ability to germinate. Curing rapidly reduces pod water content
to about 15%, then gradually to 8-10%. The use of high temperatures or brutal
drying is not recommended.
Pods can either be naturally or artificially cured. In arid savannah areas, uprootedgroundnut plants are inverted, arranged in small heaps and left to dry for one or
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two days. These are then assembled into large stacks with the pods placed towards
the inside, preferably forming a central aeration chimney. In humid areas, the
uprooted plants are dried for several days on wooden racks (stack poles) or on
raised platforms before stripping. Pods are then cured in thin layers, small bagsor baskets.
Under mechanized farming systems, combine harvesters collect windrows, strip
and clean pods in one single operation. The pods are then artificially cured in
drying trailers. Air flow temperature should be 5-6C above ambient tempera-
ture but should not exceed 35C. Optimal depth varies from 0.6 to 3 meters
according to pod water content and the type of curing equipment used.
2.2 Stripping/Winnowing
Pods are stripped at about 2 to 6 weeks after harvesting, when the pod water
content stabilizes at around 10%. This operation consists of separating the pods
from the vegetative parts of the plants (vines). In traditional farming systems,
manual stripping is the rule. Pods are individually detached from the vines and
therefore dry very quickly stabilizing at 6-8% moisture content. The process
results in a perfect quality product. Pods are separated from the vines but are
kept intact. This technique is used for the production of edible or confectionery
groundnuts in order to minimize pod damage and contamination byAspergillusflavus. However, stripping is most often done using sticks or flails. These reduce
the heap of groundnut plants to mixture of chopped vines and partially broken
pods that are then separated by winnowing.
Several types of mechanical combines can be used to strip groundnut windrows
with less than 10% moisture content. The operation of these combines is based
on the following principle. Groundnut plants are manually fed, pod first, into
the combine. Stripping is achieved by friction between the stripper bars against
the base of the plant and the pegs. The stripped product is evacuated across a
counter stripper made up of a cylindrical grid. Large pods retained by the grid
are carried along by the rotation of the combine. Pods are then stripped a second
time. A built-in blower separates the trash from the finished product. The intake
speed, selection of the grid, combine rotation speed and airflow speed must be
regulated (by adjusting the opening of the air intake shutters).
Under mechanized farming systems, modern digging and combining equipment
(high capacity machines) considerably reduce the operation time. This can leadthe producer to strip an insufficiently dried product. Although this is not important
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in confectionery or edible groundnuts, it can damage seeds by causing
microscopic lesions that alter their ability to germinate.
3. Seed processing
3.1 Sieving
This operation is generally done on the farm or at the collecting point. The
classic sieve consists of a hexagonal or cylindrical cage made from bars. It allows
part of the trash including sand, straw and broken pods to be eliminated. However,
it cannot eliminate pods of other varieties, empty pods (pops), partially filled or
immature pods. This is the most basic cleaning operation.
3.2 Density separator
Groundnuts that have been stripped and winnowed using traditional methods
are still highly contaminated by trash. A density separator can be used to get
good quality seeds with a high level of varietal purity, good maturity and absence
of foreign bodies and empty pods (pops). This process allows improvement of
seed quality during drought years and it consists of two elements:
a shaker, equipped with sieves adapted to the treated variety that eliminate
trash (sand, straw, stems) and undersized pods;a blower with adjustable airflow that runs along a sloping surface. Pods are
separated, while falling through the air stream, according to density. Pops
and partially filled pods are ejected outside whereas full pods fall into a
collecting bin.
The shaker and the blower are motorized (electric or gas engine). Gas engines
must be equipped with an oil bath filter since the machine operates under rather
dusty conditions. Adjustments can be made using a yield valve on the feeding
tray. Adjusting the slope of the shaker sieves, the airflow valves or the lowerplate of the sloping surface permits regulation of the reception opening for
good pods (the smaller the opening, the greater the segregation based on pod
weight).
Density separation considerably improves the quality of seeds in hulls, especially
after a year of drought. For Virginia type groundnuts, seed yield is increased by
an average of 9%. This translates into a mean decrease of 10 kg of seeds in shell
per hectare.
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3.3 Packaging
Pods can easily be stored in bulk following the recommendations outlined in
paragraph 4.2. Storage in clean jute or woven polyethylene fiber bags ensuresthe best protection of groundnuts and facilitates manipulation of stocks (manual
or palletized). Groundnut seeds must only be stored in bags or drums according
to recommendations presented in the following chapter. Each bag must be
properly labeled. Labels must show batch origin, year, level of multiplication,
seed weight and eventual phytosanitary treatments.
4. Seed storage and conservation
Groundnut can either be shelled or stored in hulls (improved seeds, communalstocks, buffer stocks of shelling plants).
Seeds in hulls are less exposed to different deteriorating agents and can be
conserved quite well for short periods. When stored in heaps, pods must be
treated with layers of insecticide followed by a final overall treatment. This
requires extensive waterproof storage areas or high capacity warehouses (600-
800 tons). Handling costs are proportionally high and could be minimized by
only storing properly cleaned, good quality batches.
Shelled groundnuts are fragile and are exposed to various agents that cause
physical, chemical and biological deterioration. They rapidly lose their seed value
when stored under natural conditions, especially in tropical areas. The height of
stacked bags should be limited to avoid crushing the seeds. Shelling methods
strongly influence seed quality (see chapter on industrial seed processing).
4.1 On-farm storage of pods
Farmers only keep limited quantities of groundnuts because of financial and
logistical reasons. They rarely distinguish between seed groundnuts and those
destined for sale (or their own consumption). Protective insecticides are rarely
used since farmers consume some of the groundnuts themselves. In humid tropical
areas with two rainy seasons, farmers store their seeds in a ventilated area where
they fumigate them. This storage method is absolutely inappropriate and generally
leads to considerable losses caused by insects and fungi (more than 30%). Farmers
can equally use communal facilities for storing large quantities. However, co-
management is often problematic for three reasons: contamination of the entirestock by poor quality batches, lack of confidentiality and restrictions to seed
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withdrawals to satisfy the farmers financial needs. Groundnut storage is often
conducted by salespeople who are not concerned about quality in general and
even less so by the specific requirements needed for conserving seed quality.
4.2 Collective or industrial storage
Pods must be stored according to well-defined technical recommendations in
order to provide a quality product and to ensure profitability.
Groundnuts should be stored as follows:
collect quality raw material (well filled mature pods), clean, free from visible
insect damage, well cured (6-8% water content);
clean storage facilities;treat storage facilities and seeds (paragraph 5);
check seeds regularly during storage (every 15 days or once a month
according to storage period).
4.3 Storage of shelled groundnuts
This system is rarely used on farms since shelled groundnuts are more fragile
and require expensive, hermetically sealed packaging (plastic or metallic drums).
After shelling, specific procedures must be followed in order to ensure seed
quality. Two processes are recommended: refrigerated storage and controlled
or modified atmosphere storage.
4.3.1 Refrigerated storage
This system is simple, tried and tested and results in excellent long-term storage
(over three years). However there are certain technical and financial constraints:
the stock is physically blocked in the store during the entire storage period;seeds must all be unpacked at one time and certain precautions must be
taken. For example, the temperature must be increased gradually, especiallyduring the rainy season and seeds must be rapidly used (within a few weeks)before they lose their viability;the cost increases sharply with storage time because energy consumption is
high.
4.3.2 Storage under controlled or modified atmosphere
Seeds are placed and maintained in anoxic conditions in either a complete vacuum
or in a modified atmosphere (vacuum replaced with Nitrogen or Carbon dioxidegas).
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Seeds can be maintained under these conditions for medium term periods (18-
24 months) by using extruded multi-layered packets that have a high mechanical
resistance and are impermeable to gases. A package thickness of 60m is adequate
for small quantities of up to 1 kg (e.g. storage of collection samples) however athickness of 90m is recommended for larger quantities (1-10 kg). This isespecially recommended for vacuum packaging where stretching is an importantconsideration. Controlled atmosphere storage is not only cheaper thanrefrigerated storage but there are also no chemical residues on the seeds (seeds
can be untreated). Seeds are therefore not hazardous and can be used without
special protection or authorization. Resistance or tolerance to pesticides can
also be avoided.
Anoxia eradicates insect pests especially the groundnut seed beetle. Trials wereconducted in Senegal on seeds that were artificially infested with C. serratus
and packaged under vacuum for 1-42 days (complete vacuum at 0.26 atm,
compensated vacuum (0.79 atm) with technical Nitrogen (98% N2) or with
additional CO2). In all cases, beetles were completely eradicated in less than 21
days.
Seeds packaged with Nitrogen, either with or without addition of CO2
under a
slight vacuum are completely viable after 18 months of storage at ambient
temperature. Seeds must be stored in a well-ventilated area and protected fromrodents that could damage the bags. Leakage of air into the packets is the maintechnical problem. In order to avoid this, the sealing machine must be properlyadjusted (welding quality), the bags must be of good quality and particular caremust be taken during handling. The seed value of the product depends on itsinitial quality and careful compliance with specifically adapted curing and shelling
techniques.
4.4 Some technical aspects of the industrial preparation of ready-to-use
groundnut seeds
An experiment was conducted in Senegal on the use of ready-to-use coated
groundnut seeds to improve financial and technical management at all stages of
the supply chain. All the difficulties associated with managing seeds in hulls are
avoided using this process:
minimize the volume to be stored;avoid losses and cheating caused by contaminants (sand, soil, other waste,etc.);
eliminate bad farmer practices (partial self-consumption of seeds, absenceof insecticide treatment, incorrect fungicide application).
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Although coating technology offers many advantages, it requires careful
inspection of industrial handling, packaging and storage of the final product.
4.4.1 Mechanical shellingThis first step of the manufacturing process is critical to product quality.
Mechanical shelling is relatively brutal and can cause severe damage to the
seeds (splitting, cracking). Operator expertise is fundamental to reducing the
risks of visible and invisible lesions.
Operating principle
A mechanical sheller is equipped with a head made from perforated or barred
semi-cylindrical grills, which form a cage. Hulls are spread and broken by arotor inside the cage. A pre-sorting is done by a cleaning system (sieving
and blowing), designed to eliminate or collect by-products, broken or
immature groundnuts.
A grading shaker that allows unshelled groundnuts to be separated from
whole and broken groundnuts completes the operation.
Influence of batch quality on shelling
The level of broken kernels increases when immature pods are harvested,
when groundnuts have been beaten with a stick, mechanically (+10%), ortoo late (+5% per month). This also occurs when pod moisture content is
less than 5-6% (in the Sahel it can fall below 3%).
Importance of optimizing adjustments
For a batch of a given quality, the yield of whole kernels is significantly
decreased if the grills hole size is smaller than the groundnuts, if the rotor
speed is excessive and the feeding rate of the machine is too high (a feeding
regulator may be required).
These requirements slow shelling speed and allow a judicious choice to be made
between yield and quality. Since the pod size for each batch may be relatively
heterogeneous, pre-calibration of the groundnuts is recommended in order to
optimize the yield of whole seeds.
Electronic color sorting
Color sorters use color-based systems pre-set by the user. This principle
gives an excellent reproducibility of the results, with a high yield for bothvisible and invisible wavelengths.
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The sorter consists of the following equipment:
a vibrating electromagnetic hopper for precise feeding of the system;
a steeply inclined descending chute aligning, directing and accelerating the
seeds;an examination field composed of fluorescent lights, electronic optics
opposite to reference screens;
complex computerized equipment for data collection and analysis;
an ejector that uses short blasts of compressed air to blow the offending
kernel (darker or lighter than the variety standard) out of the stream of
groundnuts.
Wavelengths reflected by each object arriving in the examination field are captured
by the optical systems and transmitted to photoreceptors that transform theminto electric signals. These are then analyzed by the computerized equipment.
When a defective groundnut is detected it is eliminated by a blast of compressed
air.
The use of clean standard sized groundnuts (for adjusting sorting rate and ejection
speed) as well as a suitable environment (stable power supply, availability of
filtered and cooled compressed air and a clean area with air conditioning) are
critical for successful color sorting.
4.4.2 Seed coating
The typical coating system consists of:
a feeding tray regulating the flow of seeds to treat;
a treatment feeder to deliver the appropriate rate of chemical;
a performing system that compiles the flow of seeds and chemical in order
to ensure proper treatment rate (mechanic or electronic control);
a mixing drum to homogenize the distribution of the treatment to all theseeds (this is equivalent to a draining or pre-drying system);
a conveyor belt to transfer the seeds to the weighing-packaging area.
The principles for an optimized use of the system are:
excellent quality seeds (seed value and integrity);regular seed feeding rate;precise chemical feeding (fungicide or fungicide + insecticide);reliable and rapid control system for seed feeding;
chemical treatment adapted to the process (stable active ingredients, slowdecanting, good coating ability) and to the local soil micro flora.
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5. Phytosanitary protection of stored seeds
Control of storage pests is of critical importance. This is even more so in tropical
countries since agricultural production does not always meet demand. Local
environmental conditions are also favorable to pest development.
Groundnuts characteristically form their pods in the soil and are therefore
vulnerable to attack by pests such as termites (Isoptera) and millipedes (Myrapoda
and Diplopoda). These can cause yield losses and reduce the quality of the
harvested crop by damaging hulls. These lesions become gateways for fungal
infection, notably Aspergillus flavus, the species responsible for aflatoxin
contamination.
Severe attack by seed bugs (Aphanussordidus, Heteroptera: Lygaeidae) are
sometimes observed on drying pods in the fields. The nymphs and adults feed
by making fine perforations in the hulls. This causes very little visible damage
but causes seed desiccation and greatly reduces seed viability.
Rodents also cause field losses to the drying crop. They are of variable diversity
and importance, however, there are two main species: one diurnal species, the
stripped ground squirrel (Xeriuserythropus) and one nocturnal (Cricetemys
gambianus).
The principle stored product pests, the seed bug (Heteroptera: Lygaeidae) and
the groundnut seed beetle (Caryedoncerratus) can cause significant damage.
Other insects, particularly Khapra beetles (Trogodermagranarium E.), as well
as flour beetles, Triboliumcastaneum H. and T. confusum are also important,
especially on shelled groundnuts.
The groundnut seed beetle is the most formidable long-term storage pest (Gillier
& Brockele-Morovan, 1979). The larva develops inside the pods and is therefore
protected from insecticidal dusts and sprays.
However, local farmers tolerate damage caused by this pest, as long as losses
are not spectacular. The detection of seed beetle damage and hence the decision
to apply treatment is sometime too late. The possibility of future attack is
unrecognized by farmers since they are unaware of the multivoltine life history
of certain pests. Farmers tolerate a certain level of damage since they accept the
idea that the pests take their share of the harvest! Such fatalism is an exampleof the ambiguous relationship that farmers have with their environment.
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5.1 Insect control
5.1.1 Contact treatments
Future stacking sites must be treated with insecticide dust before windrows andstacks are formed for drying the groundnuts. A peripheral band should also be
treated to protect the site. Groundnuts are thus protected against termites and
seed bugs. Storage areas, containers, drums, bags and storage equipment
(conveyors, etc.) must be treated before storing groundnuts. Cleaning these
areas can be followed by fumigation or spraying with insecticides. Pesticides
are applied using a sandwich technique. Seeds are dusted during bagging, and
then an insecticidal dust is applied between each layer of bags.
Organophosphates are contact insecticides currently used. Bromophos (500 g
of 2% dust/ton) or idofenphos (1000 g of 2% dust/ton) are most commonly
used products. Other available products with long residual activity include:
- organophosphates: ethyl-pyrimiphos (Actellic), methyl-chlorpyriphos
(Reldan). Their residual activity is low in open air but exceeds 6 months
on stored seeds protected from light;
- syntheticpyrethroids: Deltamethrine (K. Othrine).
Contact insecticides ensure good protection against insects once groundnutsare not previously infested. For this reason, preventive fumigation of seed
groundnuts must be carried out.
5.1.2 Fumigation
Groundnut seeds (sorted pods or kernels) can be treated under airtight plastic
tarpaulins, hermetically sealed silos or warehouses in a fumigant-saturated
atmosphere. Groundnuts are currently fumigated in pyramidal heaps under plastic
tarpaulins. Bags are arranged to form a pyramid that is slightly smaller than thetarpaulin. The base is sealed with a row of sandbags.
Methyl bromide (CH3Br), long used for fumigation, is now prohibited by
international legislation since it contributes to the greenhouse effect. This product,
used in gaseous form, has an instantaneous impact on pest, eradicating all
developmental stages (eggs, larva, and adults). Hydrogen phosphide (PH3), the
only remaining authorized fumigant, is available in tablet form. Its release is
much slower than methyl bromide and its use requires absolute adherence to
manufactures recommendations in order for it to be equally effective. For this
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reason, under the arid conditions in the Sahel, a humid environment must be
created under the fumigation tarpaulin. Small, water-filled cups or dampened
bags are placed on the surface of the heap of groundnuts being treated. This
ensures a rapid gas release that guarantees immediate eradication of the pest.
The gas is produced from the breakdown of aluminum phosphide tablets
(Phostoxin). Hydrogen phosphide, also known as phosphine gas, is obtained
when its precursors (aluminum or magnesium phosphide) are exposed to humid
conditions. Tablets must be placed on small saucers in order to recuperate
powdery residues that still contain traces of aluminum phosphide. Successful
fumigation depends on several factors. The most important are: ambient moisture,
fumigant dose and fumigation duration. Fumigant dose can be reduced in airtight
treatment areas with high temperature.
Groundnuts have relatively high absorption rates for hydrogen phosphide: 50%
and 80% respectively for shelled and unshelled groundnuts with a 5-day
fumigation at 25C3. In practice, a 3-4 days treatment with a dose of 2 g/m3 and
3 g/m3 PH3can be used respectively for shelled and unshelled groundnuts stored
under tarpaulin or in fairly airtight warehouse (considering a 50% loss coefficient).
Stored groundnuts must be regularly checked for sanitary problems, and a seed
sample should be analyzed on a 3-week basis to ensure good conservation and
eventually implement corrective measures.
5.1.3 Physical and mechanical methods
These low technology methods are cheap, effective and readily available to
farmers. Several techniques are used, depending on the area.
Groundnuts are mixed with powdered minerals (ashes, sand, etc.) that act
as abrasives or physical barriers.
Hermetically sealed containers in which anoxic conditions limit insect
development.
Temperatures are bellow (40-45C) the optimum for
insect development.
3 Laboratoire Denres Stockes, 33150 Cenon - France
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Solarisation of groundnuts under plastic or polyethylene mulching
(thermosolar treatments) which greatly affect bruchids. Precautions must
be taken to avoid deterioration of the germinative capacity of the seeds.
6. Seed physiology
Planting non-viable seeds that cannot germinate and therefore ensure a good
harvest, is the farmers greatest risk. Determining seed crop value is the ultimate
objective of any analysis. However, parameters that determine seed quality may
be prioritized differently, depending on the user. There are recommendedanalytical methods based on standardized international seed trading guidelines.
These have been ratified within the framework of the International Seed Testing
Association (ISTA).
6.1 Germination
Germination is defined as the appearance and development of the embryo, to
form the essential organs of the seedling. The seeds ability to produce a normal
seedling under favorable conditions can be determined by examining these organs.
The mature groundnut seed is made up of an embryo comprised of two
cotyledons, a short hypocotyl, the plumule and the primary root. The plumule isformed by a central axis and the two cotyledon axes. It already contains nineembryonic leaves. These essential organs originate from tissue differentiation
during the embryos development inside the seed.
Viable seeds begin germinating when placed in a favorable environment
(temperature, moisture, and oxygen). Germination takes place in several stages:
imbibition;activation of enzymes;
growth of the embryo;rupture of the testa;elongation and emergence of the radical;
growth of the terminal bud and embryonic axis.
Imbibition is based on the seeds chemical composition, water availability in its
environment and the permeability of the testa. Protein-rich seeds need to imbibe
2-5 times their dry weight in water to initiate germination. This is relatively high
when compared to certain sugar rich cereal species. These need to absorb only
one and a half to twice their dry weight in water. In order to germinate, legumes
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and cotton need a minimum water content of 50-55% whereas cereals need
30-35% which is close to the observed water content at physiological maturity.
Water activates the enzymes responsible for hydrolysis of nutritional reserves(lipids, sugars and proteins). It is essential for transport and utilization of the
simplest and most mobile components (glucose, amino acids, etc.) by the growing
embryonic axis. Enzymes catalyze the reaction needed for the synthesis of new
material required for tissue differentiation and growth of the embryo.
Germination in peanuts is epigeal. The cotyledons and the sprout are carried
above the soil by the elongating hypocotyl. Seed viability can be determined by
germination test. Four repetitions of 100 seeds or eight repetitions of 50 seeds
(a total of 400 seeds are used). Seeds are equally spaced on a moist substratethen placed in an incubator at 30C and 90% RH. Seeds are evaluated after five
days (germinative vigor) or 10 days (germinative ability). They are also classified
as normal seedlings, abnormal seedlings and ungerminated seeds.
6.2 Dormancy and methods for breaking dormancy
Dormancy is a natural phenomenon in the plant kingdom. It is defined as the
inability of newly harvested seeds to continue their development under favorable
environmental conditions (temperature and humidity). Generally, dormancy isan absence or a significant reduction in seed viability, even under favorable
conditions. Dormancy is an adaptation that allows plant to survive particular
climatic conditions. Seed germination is spread over time since the intensity of
dormancy varies within a seed population.
Natural factors or climatic changes can break dormancy. It is absent in Spanish
and Valencia type groundnut or is naturally broken several weeks after seed
maturity. It can cause pre-harvest germination in the field when harvesting is
delayed and the soil is still moist (irrigation, end of season rains) and even during
storage in unseasonably wet periods. This type of unwanted germination
considerably reduces seed yield and quality; such seeds are usually downgraded
and used for oil production. Virginia type groundnuts have a longer dormancy
of four months or more.
Endogenous metabolic inhibitors cause dormancy in groundnuts. These are
generally enzymes that block hydrolysis of nutrient reserves and nutrient transport
to the embryo. The synthesis of new material is thereby inhibited.
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Previous work has shown that product such as ethylene (3.5ppm induces excellent
germination). Ethephon can also be used to break dormancy in groundnuts.
Ethephon or ethrel, originally a growth regulator, progressively decomposes
into mainly ethylene as well as several other substances. It is available in liquidor powder form. The powder is added to the fungicide-insecticide mixture and
the liquid is sprayed onto untreated seeds. Heat treatments can also break
dormancy (40-45C for 15 days) but this long, slow treatment is not very
convenient.
Groundnut Seed Project GSP
Contact address / Principal addresses
Project Executing Agency (PEA), Farid WaliyarICRISAT, Patancheru, 502 324, Andra Pradesh, India
Bonny Ntare, Project Manager
ICRISAT-Bamako, B.P. 320, Bamako, Mali