Contributors to this page: CIMMYT – Wheat, Mexico (Thomas Payne), 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).
Planting and cultural practices for characterization
A genebank is constrained by local environments that may be divergent from ‘best practice’ defined environments.
- Choose a field in which the previous crop was preferably a non-cereal crop, or was kept in fallow.
- Fields should be fenced to prevent grazing, located away from bird roosts and rodent dens, and kept free of noxious weed species.
- Soils should be plowed and disked prior to sowing to prepare a uniform seed bed.
- Higher elevations and latitudes have lower night temperatures, which slow the growth of seedlings, so earlier planting dates are necessary to establish the stand.
- Later dates of seeding are recommended to prevent excessive growth in the autumn at lower elevations and latitude where night temperatures are higher.
- Planting too early may produce excessive early season growth and thereby use excessive amounts of moisture and nutrients.
- Planting too late may increase the possibility of wind erosion due to poor ground cover and the danger of cold damage for autumn sown cereals. Later plantings will also mature a few days later.
- Date of planting and seeding rate should coincide with local farmers’ best practices.
- Six-row plots are recommended.
- The distance between rows should be 25-30 cm.
- Plot length will vary depending on the amount of harvested seed required to fulfill all conservation and testing (phytosanitary, germination, characterization) requirements.
- Regeneration, multiplication and characterization are often done at the same time, to save time, space and effort.
Characterization and harvested area
- The four centre rows should preferably be used for characterization and seed harvest.
- Seeding rates equivalent to 50-100 kg/ha should be used. This is equivalent to 5-10 g/m2 (or 5-10 g seed / 3 m row).
- For tall and lodging susceptible material, leave a gap between plots or plant alternate plots with non-cereal crop species, to avoid entangled culms and subsequent grain mixtures between accessions prior to and during harvest.
- Each row should be labelled with a proper, highly visible label, with information on field location name, production season, nursery name, plot number and accession number.
- Labels used should withstand weathering and high sun light intensity.
- Normally un-replicated control varieties should be periodically replicated throughout the nursery trial (e.g. every 20th plot).
- For special-purpose characterization, or for more rigorous statistical analysis, full experimental trial replication may be necessary.
Standard check cultivars
- Local check varieties should be used at standardized intervals.
- They should be distinctive in appearance.
- They should be adapted to the multiplication environment.
- They should have a local “average” phenology and stature (flowering, maturing and plant height) allowing relative characterization measurements with adjacent plots.
Time of day for data collection
- Field data are best collected in the morning as this is generally the best time for consistent characterization of traits such as flowering. It may also be the best time also for the effectiveness of the observer.
- Post-harvest data can be taken any time, but for efficient use of time, a good practice is to alternate field work in the morning with post-harvest characterization indoors in the afternoon.
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Morphological descriptors for characterization
See lists for small grain descriptors developed by IBPGR (now Bioversity International) and partners:
Key access and utilization descriptors for wheat developed by Bioversity International and an International Advisory Group (2009).
Revised descriptors for wheat (Triticum spp.) developed by IBPGR (now Bioversity International) Secretariat, Rome and CEC Secretariat, Brussels (1985).
Descriptors for wheat and Aegilops developed by IBPGR (now Bioversity International) (1985).
Rye and Triticale descriptors developed by IBPGR (now Bioversity International) (1985).
Pictures for characterization
Sufficient detail should be captured in images to taxonomically identify the plant and demonstrate the traits that show variation.
- Take images for character(s) which may be difficult to describe verbally.
- Store photos in a database file linked to other accession specific data.
Herbarium samples for characterization
It may be advisable that herbaria specimens are to be taken and stored for future reference during field regeneration, particularly for primitive and wild relatives. Sufficient detail should be captured to taxonomically identify the plant and demonstrate the traits that show sufficient differentiable variation.
- Take and store herbaria vouchers for future reference and taxonomic verification.
- Collect plants with leaves, flower spikes and seeds as well as roots.
- Spread plants open before pressing.
Molecular descriptors for characterization
SSR markers should be employed to genotype germplasm subsets (because of their availability and relative ease of use), following USDA-National Small Grains Collection recommendations. Note: Technological developments are progressing so quickly in this field that suitable methods and procedures used should be determined at each period of characterization.
- Initially, research should be done to select a genotyping maker panel for each species consisting of at least 48 SSR markers.
- To do this, available SSR primer sets from the respective species should be screened across a panel of at least 16 diverse genotypes from the collection to determine the marker polymorphism information content (PIC).
- The 48 most informative markers should then be used to genotype the complete core set using the fragment analysis on the ABI genetic analyzer in a 384-well format.
- To eliminate variation due to heterogeneity within accessions, single-plant-selections for each accession should be generated for genotyping.
- Resulting data should be analyzed to better understand genetic variation within the collection, including the relationship between variation and geographic origin of accessions.
- To assess within-accession diversity, sets of 100 accessions should be chosen for each respective species. Within each of these accessions, five seeds should be randomly chosen for SSR analysis.
- Data should be analyzed to better quantify the within-accession variation of the collection.
More details about molecular protocols can be found at: CIMMYT’s website (1.9MB)
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Recording information during characterization
The following information should be collected and recorded:
- Minimum passport data.
- Donor’s details (name, institution, country).
- Germplasm Acquisition Agreement (GAA) status.
- Standard Material Transfer Agreement (SMTA) or MTA status.
- Genus, species and sub-species.
- Accession identification number(s).
- Accession ancestral pedigree, cross and selection historical data.
- Botanical status (wild, traditional cultivar or landrace, breeding or research material, improved cultivar, other, or unknown).
- Collection mission data.
- Collection site latitude, longitude and elevation.
- Date and location of regenerations.
- Minimum requirements for characterization traits:
- Growth Habit.
- Days to Heading.
- Plant Height.
- Awn Type.
- Awn Colour.
- Glume Colour.
- Hull Cover.
- Grain Colour.
- See also the list for small grain descriptors developed by Bioversity International and partners.
- Standard methods and scales for reporting descriptor traits can also be found under the respective crop “List of Descriptors” here.
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References and further reading
Bioversity International, CIMMYT. 2009. Key access and utilization descriptors for wheat genetic resources. Bioversity International, Rome, Italy; International Maize and Wheat Improvement Center, Mexico. Available here.
CIMMYT. 2005. Laboratory Protocols: CIMMYT Applied Molecular Genetics Laboratory. Third Edition. Mexico, D.F., CIMMYT. ISBN 9686923306.
IBPGR, CEC. 1985. Descriptors for wheat (revised). International Board for Plant Genetic Resources Secretariat, Rome, Italy; Commission of European Communities Secretariat, Brussels. Available here.
IBPGR. 1985. Descriptors for Rye and Triticale. International Board for Plant Genetic Resources Secretariat, Rome, Italy. HTML version available from: http://www.bioversityinternational.org/index.php?id=19&user_bioversitypublications_pi1[showUid]=2265. Date accessed: 16 May 2010.
IBPGR. 1985. Oat descriptors. International Board for Plant Genetic Resources, Rome, Italy. HTML version available from: http://www.bioversityinternational.org/index.php?id=19&user_bioversitypublications_pi1[showUid]=2209. Date accessed: 16 May 2010.
IBPGR, Information Sciences/Genetic Resources, University of Colorado (USA). 1978. Descriptors for Wheat and Aegilops. International Board for Plant Genetic Resources, Rome, Italy. 29p. Available here.
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