Sample Processing


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Page compiled by: Bioversity International/ILRI, Addis Ababa, Ethiopia (Alexandra Jorge); ILRI, Addis Ababa, Ethiopia (Jean Hanson) including information extracted from: Rao NK, Hanson J, Dulloo ME, Ghosh K, Nowel D and Larinde M. 2006. Manual of seed handling in genebanks. Handbooks for Genebanks No. 8. Bioversity International, Rome, Italy. 147pp.

What is sample processing

The processing of seeds or plant material is the preparation of the samples to be stored. This is directly linked to the method of conservation, i.e. seed cleaning and drying is related to seed conservation while extraction and disinfection of plant material is related to tissue culture or cryopreservation. Therefore, for practical purposes in this presentation this is incorporated within each conservation method.

Use the arrow to view the slides. (Photos 1,3,4 by ILRI, 2 by ICARDA, 5 by Bioversity)

 Seed processing is usually done in four main steps:

Seed cleaning
Seed drying
Seed moisture content determination
Seed packing

Seed cleaning

Seed cleaning is the removal of debris, physical contamination, inert material, damaged and infected seeds and seeds of other species. It is essential to improve the quality of samples and should be done immediately after harvesting or as soon as the material arrives at a genebank, before storage.

Why it should be done

Steps of seed cleaning


Seed threshing is the separation of the grains from the straw either by impact, friction or combing action. It can be done manually or with threshing machines.


The first cleaning usually separates seeds from debris, physical contamination and inert material. It can be done manually or with cleaning machines.

Visual inspection

This is important to check and prevent further spread of insect and fungal damage and remove damaged or empty seeds.

Final cleaning

This is when damaged and empty seeds are identified and removed. It is usually done manually.

Purity analysis

Purity is an expression of how ‘clean’ the seed lot is.

ISTA (2005) specifies a pure seed faction to contain:

Information on actual seed lot composition is important; purity analysis serves as a guideline to determine the necessity of further cleaning. During purity analysis, each ‘pure’ seed fraction from the working sample is separated from the inert matter and other seeds.

Purity (%)   =     Weight of pure seeds (g) x 100
Total weight of working sample (g)

Documentation of information about seed cleaning

It is important to file all the relevant information about the cleaning process for future reference. The information may be relevant to explain germination test results or contamination in the future.

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Seed drying

Seed drying is the reduction of seed moisture content to recommended levels for storage using techniques that are not detrimental to seed viability. It should be done as soon as possible after clean seeds arrive in a genebank, to avoid deterioration and to reduce the moisture content in the seed. High moisture promotes respiration and growth of seed embryos, insects and fungi.

Seed samples are usually kept in paper, mesh or cotton bags in well aerated and cool environments (with low relative humidity) for a few weeks to dry.

Why it should be done

Steps of seed drying

For more detailed information on seed drying see pages 36-49 of the Handbooks for Genebanks No. 8. (Available here).

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Seed moisture content determination

Seed moisture content is the amount of water in a seed and is expressed in terms of the weight of water contained in a seed. The moisture content is one of the most important factors that determines the rate at which seeds will deteriorate in genebanks. It is usually carried out with oven-drying methods or with moisture meters.

Why it should be done

Steps of moisture content determination


Pre-drying is obligatory if seeds are wet and their moisture content is suspected to be above 17% (10% for soybean and 13% for rice); it should be conducted prior to moisture content determination by oven-drying.

If pre-drying is required, proceed as follows:


Some seeds require grinding into smaller particles to have uniform and complete drying. The table below provides a list of species for which grinding is obligatory (ISTA, 2005).

Arachis hypogaea
Avena spp.
Cicer arietinum
Citrullus lanatus
Fagopyrum esculentum
Glycine max
Gossypium spp.
Hordeum vulgare
Lathyrus spp.
Lupinus spp.
Oryza sativa
Phaseolus spp.
Pisum sativum
Secale cereale
Sorghum spp.
Triticum spp.
Vicia spp.
Zea mays

Moisture content methods

Recommended methods vary with each species. The table below provides the suggested methods of moisture determination for some important crops and forages (ISTA 2005).

Low-constant temperature oven method (105oC for 16 hours)

Castor (Ricinus)*
Pepper (Capsicum)
Cotton (Gossypium)*
Eggplant (Solanum)


Falseflax (Camelina)
Flax (Linum)
Groundnut (Arachis)*
Onion (Allium)
Radish (Raphanus)
Sesame (Sesamum)
Soyabean (Glycine)*
All tree species
High-constant temperature oven method (130oC for 1 hour)
Alfalfa (Medicago)
Asparagus (Asparagus)
Barley (Hordeum)*
Bean (Phaseolus)*
Beet (Beta)
Bentgrass (Agrostis)
Bermuda grass (Cynodon)
Black salsify (Scorzonera)
Bluegrass (Poa)
Brome (Bromus)
Buckwheat (Fagopyrum)*
Canarygrass (Phalaris)
Caraway (Carum)
Carrot (Daucus)
Chervil (Anthriscus)
Chickory (Cichorium)
Chickpea (Cicer)*
Clover (Trifolium)

Cocksfoot (Dactylis)
Cress (Lepidium)
Crested dogtail (Cynosurus)
Cucumber (Cucumis)
Cumin (Cuminum)
Dallisgrass (Paspalum)
Fescue (Festuca)
Foxtail (Alopecurus)
Lettuce (Lactuca)
Lupin (Lupinus)*
Maize (Zea)*
Millet (Panicum)
Oat (Avena)*
Parsley (Petroselinum)
Pea (Pisum)*
Rhodes grass (Chloris)
Rice (Oryza)*


Rye (Secale)*
Ryegrass (Lolium)
Sainfoin (Onobrychis)
Serradella (Ornithopus)
Sorghum (Sorghum)*
Squash (Cucurbita)
Sweetclover (Melilotus)
Tall oatgrass (Arrhenatherum)
Timothy grass (Phleum)
Tomato (Lycopersicon)
Trefoil (Lotus)
Tufted hairgrass (Deschampsia)
Velvetgrass (Holcus)
Vetch (Vicia)*
Watermelon (Citrullus)*
Wheat (Triticum)*

Calculation of moisture content percentage

Calculate the moisture content on a wet-weight basis using the following formula:

Moisture content (%) = W2 – W3 x 100

W1 = weight of container with lid;
W2 = weight of container with lid and sample before drying; and
W3 = weight of container with lid and sample after drying.

Documentation of information about seed moisture content

This is important to file all the relevant information about the seed moisture content for future reference.

For more detailed information on seed moisture content determination see pages 28-35 of the Handbooks for Genebanks No. 8. (Available here).

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Seed packing

Seeds are packaged to:

For many crop species, keeping seeds at low moisture content improves longevity during storage. Maintain low moisture during packing by:

Different types of containers are available for packaging; the choice depends on storage conditions and species (size, shape and sharpness). It is important that the packing and labelling material be completely impermeable to water, withstand freezing and is suitable for long-term use. Frequently used containers include glass bottles, aluminium cans, laminated aluminium foil packets and plastic bottles.

Different types of containers have advantages and disadvantages.

Correct and clearly written labels are extremely important in germplasm collections to keep track of packets during storage:

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References and further reading

ISTA. 2005. International Rules for Seed Testing. Edition 2005. International Seed Testing Association, Bassersdorf, Switzerland. ISTA homepage available from:

Rao NK, Hanson J, Dulloo ME, Ghosh K, Nowel D, Larinde M. 2006. Manual of seed handling in genebanks. Handbooks for Genebanks No. 8. Bioversity International, Rome, Italy. Available in English (1.5 MB),  Spanish (1.4 MB) and French (1.9 MB).

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The Genebanks

The 11 CGIAR genebanks currently conserve 730,000 of cereals and grain legumes, forage crops, tree species, root and tuber crops, bananas and crop wild relatives.