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Sample processing of forage legume genetic resources

Contributors to this page: ILRI, Ethiopia (Jean Hanson); ICARDA, Syria (Ahmed Amri, Kenneth Street, Ali Shehadeh, Natalya Rukhkyan); GRCTPL, Australia (Richard Snowball); Bioversity International/ILRI, Addis Ababa, Ethiopia (Alexandra Jorge).

Contents:
Seed cleaning
Seed drying
Seed moisture content

Seed cleaning

This is the removal of physical contaminants from plant materials after harvesting, before storage. Legume seeds are hard and there is no physical damage during cleaning. All contaminants should be removed because of space constraints and costs of storage.

Legume pods should be threshed and cleaned immediately after harvest or soon after they arrive at the genebank to avoid infestation with bruchid insects. Many legume pods are dehiscent and open readily during drying when spread out in thin layer with sufficient air circulation.


Drying pods of forage legumes before threshing (photo: ILRI)

From uncleaned sesbania seeds (left) to clean sesbania seeds (right) (photos: ILRI)

Visual inspection of seeds (final hand cleaning)

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 further spread of insect and fungal damage.
According to the International Seed Testing Association rules, the following steps should be followed:

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Light box used for visual inspection of seeds
(photo: ILRI)

Separating_seeds_on_a_flat_lit_surface.jpg

Separating seeds on a flat lit surface
(photo: ILRI)

For insect and fungal damage

For mechanical damage and empty seeds

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Sesbania seeds with insect damage (photo: ILRI)

Special treatments

Disposal of contaminated materials

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 >20years, 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

Methods

Sampling frequency

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Seed moisture determination (photo: ILRI)

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

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:

Grinding

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

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

 

Oven drying temperature

This is another standard and proven method, and the best practice is to follow the ISTA (2005) suggested methods.

Recording information during determination of seed moisture content

The following information must be recorded for each processing step:

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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: www.seedtest.org/.

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).

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.

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