Horticulture Principles and Practices

Once planted, the seed is placed into a growth chamber. Chambers are set at various
temperatures, and some even alternate temperature between night and day to simulate
natural conditions (Figure 12). Crops that were developed closer the equator usually have
a single temperature, such as wheat (20 degrees C). Native species in north America
usually require alternating temperatures, such as blue grama (20C at night, 30C during
the day).
As soon as the seeds develop discernable structures they can be evaluated. Just
because a seed sprouts does not mean it is counted as viable. All the structures must be
present and in working order for the seed to be considered normal (Figures 13 and 14).
When evaluating, the analyst separates the seed into five categories: normal, abnormal,
dead, hard, and dormant (a TZ test is used to determine dormancy). Only normal, hard,
and dormant seeds are counted as viable.
Tetrazolium Testing (TZ)
A TZ test is a quick way to determine total viability. The test usually takes 24
hours to complete, and is the primary method for determining dormancy. The steps
FIGURE 12 Typical growth
chamber. (Source: Annette Miller,
USDA-ARS National Center for Genetic
Resources Preservation. Fort Collins,
Colorado).
FIGURE 13 Triticale is grown on towels. This sample
is ready to be evaluated. (Source: Annette Miller, USDA-ARS
National Center for Genetic Resources Preservation. Fort Collins,
Colorado).
FIGURE 14 The three beans on
the left have sprouted, but are missing
primary leaves—thus they are
considered abnormal. (Source:
Annette Miller, USDA-ARS National Center
for Genetic Resources Preservation. Fort
Collins, Colorado).
292 Chapter 9 Sexual Propagation