Agriculture Reference
In-Depth Information
available in the ISTA and AOSA rules. The following discussion enumerates the different kinds of tissues
that can be identiied and their relationship to interpretation of seed viability.
Viable Tissues
Although viable tissue will appear somewhat different from species to species, it will always be stained to
some degree. Warning: some immature embryos that do not stain in initial tests later stain as germination
capability increases. Sound tissue with good vitality stains continuously and uniformly throughout, begin-
ning at the exposed surface and gradually progressing inward. Cut surfaces stain more rapidly than those
with intact membranes. Sound tissue also tends to be irm (turgid) and resilient to slight pressure from a
piercing needle.
Weaker tissues range from those which are nearly completely sound to those with varying amounts
of weak, non-stained or dead tissue. Cut surfaces of weak, deteriorating cereal grains appear grayish-red.
Brighter red in many cases is an indication of good sound tissue, especially if cut with a slightly dull razor
blade. Tips of radicles, coleoptiles and leaves are likely to show bright or darker red due to areas of active
cell division. Weak seeds tend to lack a distinct color boundary between weak and dead tissue. Weak tis-
sues that are cut longitudinally tend to appear more heavily deteriorated in thinner areas than in those with
greater thickness. Weak tissues exposed to dry air tend to shrink more readily than sound tissue.
non-viable Tissues
Weak non-viable tissues may contain considerable staining, but tend to be variable in both staining pattern
as well as in the intensity of coloration. As tissues age, the transition between stained and unstained areas
become less distinct, giving the seed a mottled appearance. The color may range from pale red or pink to
an abnormal purplish, brownish or dark grayish red. Cut surfaces may appear off-white, while underlying
tissue may appear dark red. Non-viable tissues appear limp, lack turgidity and tend to shrink excessively
upon drying. The exact line between weak non-viable tissue and sound tissue can sometimes be dificult to
distinguish without cutting into the tissue with a razor blade. However, a deinite line doesn't necessarily
exist between weak non-viable tissue and dead unstained tissue.
Dead unstained tissue is usually soft and laccid with a chalky-white or cloudy, dull grayish color.
There is usually no distinct color boundary between sound stained tissue and dead tissue.
The translation of the staining pattern to derive an estimate of seed viability requires a knowledge
of seed anatomy and appreciation of the critical areas of the embryo as well as appropriate experience.
Although there are similarities among seeds of different families, genera and species, each kind of seed has
its own unique features that inluence the interpretation of staining patterns. It is particularly important that
critical transitional areas of the embryo be well stained and sound. This includes the principal areas of the
plumule and radicle, as well as critical connecting tissues between storage tissues and the root-shoot axis.
The analyst must make all interpretations in view of the location of staining patterns and their effect on the
potential for producing a normal seedling. As in the standard germination test, hard seeds are interpreted as
normal.
Evaluation criteria for different genera are speciied in both the AOSA and ISTA TZ handbooks. In
some kinds, the entire embryo is required to be stained before the seed is considered viable. However, in
most species various combinations of unstained parts of the cotyledons, radicle or other embryonic areas
are permitted if they are not considered critical to performance during germination. It is also worthy to note
the AOSA TZ handbook has detailed procedures of TZ testing for various species grouped by families.
