Sample processing of forage grass genetic resources

Contributors to this page: ILRI, Addis Ababa, Ethiopia (Jean Hanson); Bioversity International/ILRI, Addis Ababa, Ethiopia (Alexandra Jorge).

Seed cleaning
Seed drying
Seed moisture content

Seed cleaning

This is the removal of physical contaminants from plant material after harvesting, before storage. Although awns can be removed, it is not recommended to remove glumes because this can damage the delicate caryopses.

When using mechanical threshers, carefully clean with a brush or air blower between lots to:

The final cleaning should be done by hand cleaning.

Visual inspection of seeds

Visual inspection is essential in genebanks to reach high standards of removing debris, including empty or infected seeds, needed for long-term storage. This is also important to check and prevent the further spread of insect and fungal damage. Insecticides can kill adult insects but may not kill insect larva, eggs and fungi.

According to the International Seed Testing Association rules, the following steps should be followed:

For insect and fungal damage

For mechanical damage and empty seeds

Special treatments


Seeds collected from the fields, after receiving the cold treatment to eliminate any insects (Belarus genebank)
(photo: Bioversity/ILRI by kind permission of Belarus genebank)

Disposal of contaminated material

Inspection and certification (purity analysis of seeds)

Recording information during seed cleaning

The following information should be recorded for each processing step:

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Seed drying

Method recommended in genebank standards

Drying time:

Moisture content before drying:

Moisture content for storage:

This is recommended in genebank standards (FAO/IPGRI, 1994) and experience shows that seeds remain with high viability for >20 years, when using this standard.

Critical moisture content:

The critical moisture content is the level below which further reduction in moisture content no longer increases seed longevity in low temperature storage. Critical moisture content values vary with storage temperature and species. For more information see Rao et al, (2006).

Recording information during seed drying

The following information should be recorded for each processing step:

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Determination of seed moisture content


Sampling frequency:

Standard drying periods under the drying conditions available in the genebank have been determined and so it is only necessary to measure moisture content on sample accessions once.

Calculate seed moisture content by weight loss on a wet weight basis.

Sample size:

This method follows a modified ISTA 2005 method using more replicates of smaller weight of seeds.


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

If pre-drying is required, proceed as follows:


Grinding is recommended for large seeded species such as forage oats (about 2-3 mm) to ensure small particles for efficient removal of moisture.

Grass/cereal species for which grinding is obligatory (ISTA, 2008):

Avena spp.
Hordeum vulgare
Secale cereale
Sorghum spp.
Triticum spp.
Zea mays

Oven drying temperature:

This is another standard and proven method, and the best practice is to follow the ISTA (2008) suggested methods.

Recording information during determination of seed moisture content

seeds of buffel grass harvested from debra zeit field, with the first labelled information.jpg

Buffel grass seed (photo: ILRI)

The following information must be recorded for each processing step:

References and further reading

FAO/IPGRI. 1994. Genebank standards. Food and Agriculture Organization of the United Nations, Rome and International Plant Genetic Resources Institute, Rome. Available in English, Spanish, French and Arabic.

ISTA. 2008. International Rules for Seed Testing. International Seed Testing Association. ISTA secretariat, CH-Switzerland. Available from:

Loch DS, Harding WAT, Harvey GL. 1988. Cone threshing of chaffy grass seeds to improve handling characteristics. Queensland Journal of Agricultural and Animal Sciences 45:205-212.

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.