Official Newsletter of the WANA Seed Network
No. 29,
July 2005
PDF File (378
KB)
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In this section we provide technical/practical information that seed sector staff may find useful. The guidelines are simple instructions for technical staff involved in seed production and quality control.
How to No 31: Maintaining Varietal Purity and Identity During Seed Production
Genetic purity is a major seed quality component. Almost all seed certification schemes have field and laboratory standards for varietal purity. During seed multiplication there are at least three sources of contamination affecting seed quality: genetic, mechanical and pathological. The former two have significant effects on varietal purity.
Genetic contamination: The major sources of genetic contamination are:
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Out crossing which is difficult to avoid in large-scale
crop production involving a wide range of varieties within the same
geographic area
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Volunteers from the previous crop which can be controlled
by proper rotation
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Mutation which may occur at lower rate, but is difficult
to control
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Genetic shift in cross pollinated crops which can
be minimized by proper site selection
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Mechanical admixture: The risk of physical admixture is very high in mechanized operations, the potential sources are being the seed drills, irrigation facilities, combine harvesters, trailers, trucks, seed cleaning machines, old, damaged or used bags and containers.
To minimize the risks of multiple sources of mechanical admixtures:
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Separate varieties based on crop species such as
(bread and durum wheat, kabuli and desi chickpea) or clearly visible
morphological characters such as ear rows in barley; maturity class;
plant height; seed color
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Arrange the varieties in the field and storage facilities
based on different characters
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Try to carry out operations prone to mechanical
mixing are handled in a sequence that avoids closely related varieties
are handled following each other
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Following these procedures any mechanical admixture can be easily detected in the subsequent generations of seed multiplication to take appropriate action. The morphological and phenological differences can be corrected by rouging whereas differences in size and shape can be corrected by cleaning. Abdoul Aziz Niane, Seed Unit, ICARDA, P.O. Box 5466, Aleppo, Syria; Fax: +963-21-2213490; E-mail: a.niane@cgiar.org