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PPDC Seed Botany lab

Plant Pest Diagnostics Center - Seed Botany Laboratory

Types of Samples Processed

Seed Sampling Guidelines


Quarantine tests are performed on seed moving across state and county lines and are an important part of the pest exclusion, detection and eradication program. The quarantine test requires the examination of a minimum of 25,000 seeds from each submitted sample to detect the presence of noxious weed seeds.


Regulatory tests include a noxious weed seed examination of a minimum of 25,000 seeds, a purity examination of a minimum of 2,500 seeds, and a germination test of 400 pure crop seed, from each submitted sample to determine label integrity. Laboratory procedures used for these tests are those prescribed in the Federal Seed Act. The noxious weed seed examination is similar to that of a quarantine test. The purity examination consists of a separation of pure crop seed, other crop seeds, inert matter and weed seeds. Results of this test are reported as percentages based on weight. The germination test determines the percentage of normal seedlings that can be expected to be produced in a seed lot. Four hundred seeds are planted on various types of artificial media, and are subjected to various environmental conditions deemed appropriate for the species being tested, in an effort to determine the number of normal seedlings produced under optimum conditions. Laboratory results from the noxious weed seed examination, purity examination, and germination test are compared to the seed lot label; if the results are determined to be out of tolerance with the seed lot label, appropriate action is taken by Nursery and Seed Service.


Service tests include examinations similar to those described for regulatory tests, and are conducted on a fee for service basis. The test results are reported directly to the client on formal certificates of analysis and are confidential. These documents are the basis for seed commerce throughout the world. Laboratory procedures used in service testing follow those prescribed in the Federal Seed Act, the Association of Official Seed Analysts Rules for Testing Seed, the International Seed Testing Association Rules for Testing Seed, and the Canadian Seed Act. Results of these tests may also be used for resolving contractual disputes.

Feed Investigation

Feed investigation tests include the removal, identification, and determination of viability of all weed seed found in processed livestock feed samples. Testing of these samples regulates the certification of feed mills and stops the spread of weed seed throughout the state.


These samples include identifications of specimens submitted to the laboratory by border stations, counties, other government agencies, commercial seed laboratories, medical doctors, veterinarians, archaeologists, and other researchers. These identifications are not only critical in preventing of the spread of hazardous weeds, but are often necessary for expediting importation and exportation of agricultural products, required as evidence in criminal court cases, and necessary for medical and veterinary diagnoses of poisoning cases. The identifications are often difficult and extremely time-consuming, requiring library research and/or travel to other northern California herbaria.


Investigations include tests performed to resolve disagreements between different test results on the same seed lot, to document problems with existing test methods, and for instructional purposes. Results of investigations are used as documentation for proposed changes to the Association of Official Seed Analysts Rules for Testing Seed (standardized throughout the United States and Canada).


Referee tests are performed as part of the nationally and internationally organized programs to foster standardization of methods for testing seed to promote orderly marketing worldwide.