Agriculture Reference
In-Depth Information
6
Seedling
Evaluation
The germination test is universally accepted by the seed trade, seed control oficials, and certiication agen-
cies as an objective, reproducible means of evaluating seed quality. In seed laboratory practice, germination
is deined “as the emergence and development from the seed embryo of those essential structures that, for
the kind of seed in question, are indicative of the ability to produce a normal plant under favorable condi-
tions” (AOSA, 2010). To meet these objectives, a germination test must provide a suitable environment
for a speciied duration of time to allow the “essential structures” to develop to a point where they can
be evaluated as either normal or abnormal. Thus, the philosophy of germination testing incorporates the
optimization and standardization as well as an indication of the ability to produce a normal plant under
favorable conditions. For additional insight into the philosophy of germination testing, see Chapter 5.
The science of seed testing is dynamic, particularly with respect to germination procedures and seed-
ling evaluation. In part, this is due to the paradoxical deinition of germination: do procedures used to elicit
maximum germination equate to the ability of a seed to produce a normal plant under favorable conditions?
Readers are encouraged to carefully review this chapter and the seedling evaluation handbooks of both the
AOSA and the ISTA. Accurate seedling evaluation and standardization of germination results require the
use of germination rules and seedling evaluation criteria for speciic species.
This chapter has been arranged to provide a general overview of normal and abnormal seedlings,
causes of abnormal seedlings, and ISTA seedling evaluation criteria. The objectives of this chapter are two-
fold: to present general descriptions of seedling evaluation, thus providing a learning resource regarding
this important aspect of seed testing; and to present detailed descriptions and illustrations of normal and
abnormal seedlings of representative genera and species encountered in seed testing.
oVErVIEW of SEEdLInG EVALuATIon
normal Seedlings
In the early days of seed testing, practically any seed that produced a radicle was regarded as having ger-
minated (Justice, 1961). However, tests conducted in the U.S. Federal Seed Laboratory by Goss in 1917
showed that weak and defective sprouts failed to produce plants. Thus, radicle protrusion did not always
result in a normal plant and was therefore considered a poor guide for the practical requirements of germina-
tion testing. Considerable research on seedling evaluation has been conducted since that time and resulted
in the classiication of weak and defective seedlings as abnormal. Research has also led to the establishment
of speciic guidelines for the separation of normal and abnormal seedlings from a broad spectrum of genera.
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