Horticulture Principles and Practices

FEDERAL AND STATE SEED LAWS
Federal and State laws regulate the sale and labeling of seed. Seed producers must adhere
to the seed acts of each state they sell seed in, and if seed is sold in interstate commerce
then it is subject to the Federal Seed Act. Seed act requirements stipulate that purity and
viability information be present on all seed labels. Labs help companies and growers
determine this information so they can label their seed properly.
COMMON SEED TESTS
Purity Exam
A purity exam determines the percentage (by weight) of pure seed, other crop, weed, and
inert material in a seed lot (Figure 2). The pure seed component is the desired species in
the seed lot, and the other three components are essentially unwanted material. Weeds
and other crop may appear in a sample if the field was contaminated, or if the harvesting
equipment was not properly cleaned before use. Inert material usually consists of dust,
stones, plant parts, and the like.
Performing the purity exam can be a tedious, difficult task. The sample (sent by the
seed producer) is divided into a sub-sample consisting of roughly 2,500 seeds. A seed
divider is used to indiscriminately select the seeds that the lab will test. There are many
types of seed dividers, but the most widely used is an electric Gamet divider (Figure 3).
The sample is mixed and split in half until the desired weight is obtained.
The analyst, using a microscope or a magnifying lamp (depending on the seed
size), then separates the sample into the four components (Figure 4). Each component is
FIGURE 2 This is a typical purity station. Tools
include a microscope, seed blower, and purity
bench. (Source: Annette Miller, USDA-ARS National Center
for Genetic Resources Preservation. Fort Collins, Colorado).
FIGURE 3 This electric Gamet divider is routinely
used to obtain a sub-sample for laboratory
testing. (Source: Annette Miller, USDA-ARS National Center
for Genetic Resources Preservation. Fort Collins, Colorado).
FIGURE 4 These are the four
components of a purity test.
(Source: Annette Miller, USDA-ARS
National Center for Genetic Resources
Preservation. Fort Collins, Colorado).
9.4 Seed Quality Analysis 289