Crop Genebank Knowledge Base

Viability

Viability 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:
Viablility testing
Routine monitoring

Viability testing

Laboratory methods

Describes the various recommended options, to test the viability and quality of wheat seeds. The percentage of germination of the stored seeds of the accessions determines when the regeneration of the accessions should take place and if the accession can be distributed to the users.

Type of test

Some collections advocate the use of externally contracted, accredited parties to conduct unbiased seed quality assessments.
ISTA methods and rules of determining seed viability should be routinely and widely practiced.

Number of seeds and replicates

Normally, replicates of 50 seeds totaling 100-200 seeds should be tested for monitoring seed viability.
Genetically heterogeneous populations may need 200 seeds to determine viability, whereas more homozygous accessions may need fewer seeds (50-100) to measure viability.
If the variability between the replicates is high, another germination test should be conducted with a further 100 seeds.

Pre-treatment

Viability testing should be performed with seeds that have been cleaned and dried.
Seeds may be surface sterilized with a 0.5% sodium hypochlorite solution for ten minutes to avoid fungal contamination.

Media

Petri dishes lined with filter paper that has been wet with tap water should be used for germination tests.

Temperature

Use a germinator incubator at 25˚C.

Light

12/12 hours dark/light regime.

Duration of test

Normal, abnormal and seeds lacking germination should be tallied after four and seven days to determine percent of germination.

Monitoring intervals

To ensure the viability of the seed accessions in both base and active collection.

Below four different approaches to viability monitoring intervals are given. They are all valid, but the USDA approach seems to be the most innovative!

ICARDA

An initial assessment of viability is made before an accession is added to a collection.
After five years of the initial storage, a random sub-sample from stored accessions will be subjected to a new germination test.
The above results are compared with the initial germination test results.
If the results match, the monitoring interval can be extended.
If a decline is observed, a larger random seed sample should be re-tested, and the regeneration procedures and storage facilities should be reviewed to avoid any improper conditions and procedures.

CIMMYT

Monitoring of seed viability occurs with an initial assessment, repeated at subsequent ten-year intervals.
Sequential seed viability monitoring may be reduced to five-year intervals depending on preceding seed vigour and the percentage of the germination test results (Ellis et al., 1985).
Seed viability should be monitored in both base and active collection.
Seed viability in a base collection is expected to maintain for much longer than in the active collection (Walters et al., 2005).

USDA National Small Grains Collection

Accessions are scheduled for regeneration based on a priority matrix where each accession is assigned a regeneration priority number between 1 and 9, where 1 is the highest priority for regeneration and 9 the lowest as shown in the following table:

Viability Status	Inventory Status*
Viability Status	High	Low	Critically Low
High (>70%)	9	8	5
Low (20-70%)	7	6	3
Critically Low (<20%)	4	2	1
*High = >50 g for cultivated species, >10 g for wild species. Low = 15-50 g for cultivated species, 4-10 g for wild species. Critically Low = <15 g for cultivated species, <4 g for wild species.

Viability tests are scheduled for each accession every five years.

CGN Wageningen

Testing initial germination capacity: the first test is carried out on a sample to be accessed to the genebank.
Repeating germination test: monitoring of germination capacity, after some time, of numbers already accessed to the genebank. This repeated test is done on samples at intervals specific to each crop. Each regeneration of an accession can be tested several times.
Controlling germination test: 5% of the above two germination test samples are tested twice to test the reproducibility of the test method.
Ten years after the last germination test, the test should be repeated for:
- All material with a germination capacity lower than 80% during the last determination.
- Material of crops of which: seeds reportedly have a short life span, seeds in short-term storage that show a poor storability (on the basis of breeder’s experience), where data from literature are contradictory or lacking.
After a minimum of 20 years after the last germination test and/or a maximum of 30 years after the last multiplication, these actions should be repeated for all remaining material.

Recording information during viability testing

The following information should be recorded for each processing step:

Normal germinated seeds of Wheat (photo: ICARDA)

On the petri dishes

Accession Number (unique identifier).
Replication number (number).

On the data sheets and database

Accession number (unique identifier).
Taxonomic name (taxon).
Replication number (number).
Start and end trial dates (dates).
Test method used (standard test procedure used).
Sample size (number).
Number of seeds (seedlings) germinated (results) in each category (normal, abnormal, non-germinated).
Germination percentage (counted on normal seedlings only). Seedlings should be judged as normal according to specific criteria [ISTA (2003, 2005), Association of Seed Analysts (AOSA) (2005)].

Back to top

Routine monitoring

The genebank curator must continually monitor the general conditions of the genebank infrastructure and operating procedures to ensure that conserved seed quantity and seed viability is maintained to international standards. Safety from vandalism, robbery, adverse weather, electrical failure and lack of off-site safety duplication must all be considered when reviewing the security of a collection.

Periodic monitoring of the collection’s seed inventory and seed viability is essential.
Computerized stock control systems should be used to monitor the quality and quantity of seed accessions in cold store.
Quality control flags should be used to determine when an accession is:
- (A) = Available for distribution.
- (L) = Low in seed stock, allowing an accession to be distributed but alerting the curation that a regeneration of the accession is needed.
- (S) = Low number of seeds whereby no seed distribution is allowed; and sample regeneration should occur immediately.
- (V) = When viability falls below prescribed levels.
Inventory management through use of barcoding applications may result in increased managerial efficiency and accuracy. The process of barcoding an entire collection also provides an opportunity for the entire collection’s current inventory to be taken and confirmed.

Monitoring frequency

Describes the minimum quantity and minimum viability of seeds below which they need to be regenerated.

Critical quantity

For both cultivated and wild species: 1000 seeds (to keep the integrity of the population samples as at ICARDA).
Or set at 500 seeds (as followed at IPK-Gatersleben).

Critical germination level

For cultivated wheat: 85%; for wild cereal species: 75% (or 10% less than the average value of fresh seeds, as suggested at ICARDA).
For wheat in general, set at 70% (as used at IPK-Gatersleben).
For wheat in general, set at 85%, based on the initial seed viability of 100% (as followed by CIMMYT, to ensure a large enough sample size is used to maintain the genetic integrity during the cycles of regeneration.

Recording information during routine monitoring

The following information should be recorded for each step:

Accession number (unique identification number).
Date of initial viability test (date).
Germination %, initial test (percentage).
Date of each subsequent viability test (update database with a date).
Germination percentage of each subsequent viability test update database (%).
Date of the initial storage (date).
The initial amount of seeds stored (g).
The current amount of seeds stored (g).
Thousand grain weight (g).
Date of next required viability test (one year if it is close to critical value; five years when it is above 90%).
Regeneration flag (Yes – must go for regeneration; No – no need for regeneration).

References and further reading

AOSA (Association of Official Seed Analysts). 2005. Page 113 in: Rules for Testing Seeds (Capashew Ed.), 4-0, 4-11. Las Cruces, New Mexico.

Ellis RH, Hong TD, Roberts EH. 1985. Handbook of seed technology for genebanks volume I. Principles and methodology. Handbooks for Genebanks no. 2. International Board for Plant Genetic Resources, Rome, Italy.

ISTA. 2005. International rules for seed testing. ISTA Secretariat, Switzerland.

ISTA. 2003. International rules for seed testing. ISTA Secretariat, Switzerland.

Walters C, Wheeler LM, Grotenhuis JM. 2005. Longevity of seeds stored in a genebank: species characteristics. Seed Science Research 15:1-20.

Back to top