Horticulture Principles and Practices

FIGURE 15 The essential structures of these
embryos have all stained, indicating that this seed
is viable. (Source: Annette Miller, USDA-ARS National Center
for Genetic Resources Preservation. Fort Collins, Colorado).
FIGURE 16 These lupine seeds have varying
degrees of stain. The root tips on three of the seeds
have not stained, and the cotyledons of the lower
middle seed are also void of stain: this indicates that
the seed is dead or abnormal. (Source: Annette Miller,
USDA-ARS National Center for Genetic Resources Preservation.
Fort Collins, Colorado).
FIGURE 17 Pigweed (Amaranthus
spp.) has a peripheral
embryo that must be extracted
from the seed to stain. The
embryo on the left is viable.
(Source: Annette Miller, USDA-ARS
National Center for Genetic Resources
Preservation. Fort Collins, Colorado).
are relatively simple, but it takes a good analyst to evaluate a TZ test correctly.
The seeds are imbibed in water overnight, and then the embryo is bisected (or
pierced) with a razor blade the next day. Then bisected seed is placed into TZ
solution to stain, and as the embryo respirates it soaks up the solution. The parts
of the embryo that do not respirate are dead, and they will not soak up the
solution. A chemical reaction takes place, and the live structures of the embryo
stain red. Once the seed has stained (this can take 2-48 hours, depending on the
species) the analyst ‘reads’ the TZ. Under a microscope the analyst can see all the
essential structures of the plant, and if they all have an appropriate amount of stain
then the analyst considers them viable (Figures 15, 16, and 17).
0.1 percent tetrazolium solution; the other set is left untreated. Living tissue in the seed
is stained, whereas the dead tissue remains the same color. Percentage germination is
given by the proportion of stained seeds. This test only indicates that seeds are respiring
and does not equate the respiring seed with germination.
9.4 Seed Quality Analysis 293