Official Newsletter of the WANA Seed Network
No. 32,
January 2007
PDF File (
530 KB)
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This section provides technical/practical information for technical staff involved in seed production and quality control.
How to No. 34: Control Plots in Seed Quality Assurance
Definition
Control plots are small plots sown by the seed certification agency with samples collected from seed lots produced and certified in a previous cropping season. A control plot can be used as pre-control or post-control in a seed certification scheme. If a control plot is used to monitor the quality of seed being produced in the same crop season it is called a pre-control plot. If it is used mainly to monitor the performance of the previous crop season it is called a post-control plot.
Uses of control plots
Control plots are useful tools for:
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Monitoring the accuracy of field inspection procedures applied on seed lots approved the previous season |
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Evaluating the performance of field inspectors who conducted inspection of seed lots approved the previous season |
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Monitoring the quality of seed lots harvested during the current season for approval by seed certification agency |
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Training of field inspectors on characters of existing and/or newly released varieties or any anticipated potential contamination |
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Identifying seed production fields planted with low quality seed as revealed through early inspection of control plots. |
Procedures for control plots
According to OECD Seed Schemes, the 'standard sample' of a variety is the official standard against which all other seed samples of the variety will be compared. The sample must not differ significantly in any character from seed used for official tests on which the variety is accepted.
Sample size
Seed samples of appropriate quantity, determined based on the seed rate of a given crop and the certification standards to be enforced, are collected from the seed lots to be controlled after processing and treatment. The sample should contain three times the number of plants in which one contaminant is allowed in the certification standard for a given seed category. For example, in a seed category with 99.9% (1:1000) minimum varietal certification standard, a sample of 3000 plants is required (note OECD Seed Scheme requires 4n). In other words, a wheat variety with 1000-kernel weight of 40 g may require 120 g seed sown at the seed rate of 100 kg/ha for a plot, whereas a chickpea variety with a 1000-kernel weight of 1 kg, requires a 3 kg plot size at a seeding rate of 100 kg/ha.
Intensity of control plots
The intensity of control plots depends on seed category and availability of resources. It is essential to control all seed lots used for further multiplication and a smaller proportion of seed lots sold for commercial grain production. It may be necessary to control 100% for pre-basic and basic seed and only 30% for certified seed.
Planting procedures
Plots should be planted on land free of weeds and other contaminants to produce a clean standing crop. Similar varieties and generations should be grouped together with one standard sample for every 15 plots. The plots should be sown earlier than actual planting time, irrigated for early and even germination, and adequately managed similar to that used for seed production.
Taking observations
The plots should be examined throughout the growing season. Observations should be made to ensure varietal identity and purity in terms of the presence of offtypes and other varieties based on varietal characters and presence of seed-borne diseases.
Reporting results
The number of plants per plot should be estimated to calculate the percentage varietal purity. In some countries, pre-control plot results can be used to approve the seed lots based on the certification scheme. Abdoul Aziz Niane, Seed Unit, ICARDA, P.O. Box 5466, Aleppo, Syria, E-mail: a.niane@cgiar.org