Crop Genebank Knowledge Base

Sample processing

Sample processing of bread wheat, durum wheat, triticale and related cereals genetic resources

Contributors to this page: CIMMYT - Wheat, Mexico (Thomas Payne) and ICARDA, Syria (Ahmed Amri) with inputs also received from CIMMYT - Maize, Mexico (Suketoshi Taba); USDA - National Small Grains Collection, Aberdeen, Idaho, USA (Harold Bockelmann); CGN, Wageningen, The Netherlands (website) and IPK, Gatersleben, Germany (Helmut Knűpffer).

Contents:
Seed cleaning
Seed drying
Seed moisture content

Seed cleaning

Cleaning harvested seed using course sieves (photo: CIMMYT)

Cleaning is the removal of physical contamination from the plant materials after harvesting, before they can be stored.

Prepare labelled harvest cloth bags or paper sacks in advance of harvest.
Label both outside and inside the seed bags with the plot number, accession number and accession name.
Commence harvest when grain moisture content has reached 13-15%.
Harvest and thresh with plot combine (seeds are hard and there is no physical damage). Allow the plot combine to thoroughly clean the area between plots to avoid any mixtures and contamination.
Use a cylinder type machine to de-awn or fully thresh accessions.
Clean harvested seed with a wind-blown separator and course sieves or screens (to separate the chaff, dust and other inert materials from the samples, as well as light and empty seeds), to remove broken seeds (caused by mechanical threshing), diseased seeds, soil particles and stones of the same size and weight of the grains.
Hand cleaning allowing visual inspection for seed purity (mixtures, weed seed, diseased seed, chaff, soil, insects, etc.) is advisable (to remove contaminants and ensure initial degrees of integrity).
Dry the seeds initially, for short-term storage (see details below, in seed drying).

Visual inspection of seeds

This is a quality control that must be done after harvesting the seeds.

Spread the seeds on a flat well lit surface of contrasting colour.
An illuminated table can be used if available.
Examine dry seeds with the naked eye or under a microscope (visual inspection of the seeds is the most practical approach to ensure the seed quality and the accession integrity in a genebank).
Isolate, remove and destroy the infested/infected seeds (good quality seeds are well filled and plump and heavy).

Special treatments

Annually fumigate all temporary seed storage and seed preparation rooms and equipment against grain insect infestations.
Prevent rodents from entering preparation and storage facilities, and maintain rodent deterrents at all times.

Disposal of contaminated material

Seed, trash and plant material should be disposed of by incineration or burial at a designated site (to eliminate contaminated seed, preventing the spread and cross-contamination of insects and diseases).

Inspection and certification

A seed conservation manager or curator should be in charge of the final inspection on purity of seed material (the multistage seed inspection by the genebank curator or personnel should be required to ensure the purity of the seed accession and the genetic traits present in the germplasm accessions).

If the seed material is of insufficient purity, the deviation should be recorded in the multiplication logbook.
The curator should re-clean the material, or schedule a subsequent regeneration of the material.

Back to top

Seed drying

Methods

1st stage drying (during cleaning)

In open, well ventilated areas, allow seeds to dry to a maximum of 12% moisture content, for short-term storage (to prevent seed moulding and to preserve viability).

2nd stage drying (after cleaning)

Cleaned seed samples should be dried in a hermetically sealed, temperature and humidity controlled drying room [seed drying is the most critical genebank operation to insure seed longevity (ISTA 1993, Thormann et al. 2004, Probert and Hay 2000)].
The temperature in the room should be set at 10-20°C and relative humidity (RH) at 13-15%.
The seed samples should be dried in paper or other ‘breathing’ material bags.

Drying time

Depending on the original moisture content and the seed quantity, it may take 3–5 weeks.

Moisture content for storage

The desired moisture content to be reached is 3–7%.
Replicated, representative seed samples should be monitored for moisture content during the drying process.

Critical moisture content

Short-term storage requires a grain moisture content of 12% or less.
Long-term storage requires a grain moisture content of less than 5%.

Recording information during seed cleaning and drying

The following information should be recorded for each processing step:

All packets, sacks and bags containing seeds must be clearly labelled, identifying the accession with unique identifier(s).
Durable labels should be affixed on, and inserted into, each seed bag.
Data attributable to the accession sample should be printed on the label, including accession number, plot number, regeneration year and location, taxonomy and accession name.
Inclusion of seed and/or glume colour may be desirable to enable verification of sample identity during seed processing.
Accession number (the genebank accession number: the accessions are inventoried for long-term conservation and seed distribution).
Year of regeneration (year of regeneration of the bagged sample).
Location of regeneration (name of the experimental station, farm or field in which the regeneration trial took place).
Trial and plot number of regeneration (trial and plot number identifying the origin of the seed lot).
Taxonomy, genus and species.
Accession name (name, pedigree).
Grain or glume colour.

TIP: In the seed storage facilities, the type and the status of a seed lot must be clearly distinguishable so that seed material cannot enter a wrong process stream or activity. Some collections use coloured labels to identify different processes within their schema of accession management. CGN The Netherlands recommends that the type and/or status of seed lots be marked by means of coloured labels, which are attached to the boxes in which the material is stored. Relevant data should be noted on the labels, thus revealing the identity of the material. In addition, the location of further information about the material and where the material is stored should also be given.

Red: deviant material.
Pink: newly acquired material.
Yellow: material from third parties.
Blue: waiting for seed testing.
Green: ready for accession.
White: all accepted material.

Back to top

Determination of seed moisture content

Methods

The seed moisture content of seed accessions can be determined most accurately by the use of the air-oven method (to ensure that dried seeds have reached the optimum moisture content required for long-term conservation).
Rapid measure of whole grain moisture content is also possible using electronic moisture testers. Experience at CIMMYT indicates that electronic moisture meters are a rapid and reliable means to monitor the seed moisture content, with a difference in moisture content with the oven method of less than 1%.

Sampling frequency

Prefered method is using the electronic meter.
Sample as required to reach the desired target moisture content.

Sample size and grinding

Obtain two random samples from the seed lot to be tested, 4.0-5.0 g each and grind separately.
From each ground sample, make two 1.0-2.0 g sub-samples, treating each as two independent replicates.
Use analytical scales to weigh the samples before and after oven drying.

Oven drying temperature

Seeds with an initial moisture content of <10% before grinding can be oven dried for one hour to the constant moisture in an oven.
Dry the ground seed samples (0.5-1 mm of medium fine particles) at 130^oC in an oven for four hours (ISTA, 1993).

Recording information during determination of seed moisture content

The following information should be recorded for each processing step:

Accession number.
Moisture content determination method (oven or electronic moisture meter).
Net fresh weight in grams (g).
Drying temperature.
Time and date.
Net dry weight in grams (g).
Moisture content (%).

References and further reading

International Seed Testing Association ISTA. 1993. International rules for seed testing. Seed Science and Technology 21, Supplement.

Hong TD, Linington S, Ellis RH. 1996. Seed storage behaviour: a compendium. Handbooks for genebanks no 4. International Plant Genetic Resources Institute, Rome.

Probert RJ, Hay FR. 2000. Keeping seeds alive. In: Black M, Bewley JD, editors. Seed technology and its biological basis. CRC Press LLC. USA and Canada. pp. 375-404.

Thormann I, Metz T, Engels JMM. 2004. The Species Compendium (release 1.0; December 2004). [online]. Available from: http://www.bioversityinternational.org/scientific_information/Information_Sources/Species_Databases /Species_Compendium.html. Date accessed: 31 March 2010.

Back to top