Horticulture Principles and Practices

processing into flour or meal). However, cracked seeds can significantly reduce the
market value of the produce in other markets.
Mechanical damage may be determined by a simple laboratory procedure as follows:
1. Obtain twenty to fifty seeds (randomly selected) from the lot.
2. Place a sample in a petri dish containing a 1 percent sodium hypochlorite
solution. (If household bleach is used, it should be noted that it contains
5.25 percent sodium hypochlorite.)
3. Soak seeds for fifteen minutes.
4. Count the number of swollen seeds.
5. Count the number of swollen seeds after soaking for thirty minutes.
6. Calculate percent cracked seed as follows:
number of swollen seeds
total number of seeds
100
9.5 SEED VIABILITY AND LONGEVITY
Seeds may look healthy but fail to germinate when planted. Two other seed qualities that
are essential but not displayed on the seed envelope are viability and longevity. Viability
is a measure of the proportion of seeds in a lot that are capable of germinating. Longevity
is a measure of how long seeds remain viable. Viability is measured using germination and
tetrazolium tests. Species in the pumpkin family (Cucurbitaceae) (e.g., cucumber, squash,
and cantaloupe) remain viable for a long time (sometimes for several years), whereas
species in the lily family (Liliaceae), including onion and leek, lose viability only about
two to three months after harvesting. Seeds of pine, hemlock, and spruce remain viable
with proper storage for several years. On the contrary, seeds of maple, elm, and willow have
a very short period of viability, lasting only a few weeks. Apart from longevity inherent in
the plant species, viability of seed during storage depends on the storage environment as
pertains to seed moisture content temperature, and relative humidity.
Seed longevity depends on the species and the conditions at harvest and during
storage. Seeds should be stored only when they have attained the appropriate moisture
content (usually less than 15 percent). Seed dried to about 7 percent moisture and
under low relative humidity can be stored for a long time in a refrigerator (0 to 4°C or
32 to 39°F). Very low relative humidity of about 5 percent allows seeds to be stored
for a long time while retaining the highest level of viability. However, a relative
humidity of 50 to 65 percent maintains the viability of most seeds for about one year.
To increase longevity, seeds may be stored cryogenically in liquid nitrogen at 192°C
(313.6°F) for years. For ordinary storage, ziplock plastic bags, or bottles are
adequate containers.
Seed Viability
The proportion of seed in a
lot that is capable of
germinating.
Seed Longevity
A measure of how long
seed remains viable.
9.6 TAGGING COMMERCIAL SEED
Before certified seed can be released for sale to customers, it must be identified with an
appropriate tag. Tags are color-coded. A white tag identifies breeder or foundation seed,
a purple tag for registered seed, and blue tag for certified seed. Sometimes, a breeder may
have seed that meets certification standards and yet opt not to have it certified. Such seed
is identified with a green tag. Apart from these color codes, a seed tag displays some
basic information about seed quality and source. The interpretation of the information on
the tag is presented in Table 9–1.
9.6 Tagging Commercial Seed 295