Agriculture Reference
In-Depth Information
Part Two
Varietal Identification Tests based on Morphological, Chemical,
Growth Habits and other Characteristics
There are numerous traditional ways to test seeds for varietal identity. The most deinitive method is by ield
grow-out tests using morphological characteristics described by the breeder. The seed analyst, however, is often
challenged to make variety determinations within a very short time. Consequently, rapid laboratory methods
for varietal determination are needed. Methods described here will concentrate on techniques which can be
accomplished in a typical seed laboratory by an analyst within a reasonable period. These fall into four catego-
ries: seed morphology and appearance, quick chemical tests, growth chamber tests, and disease resistance tests.
SEEd And SEEdLInG MorPHoLoGy
The morphological features of seeds, in addition to vegetative and reproductive characters, were probably
the irst criteria used in variety testing. The most useful morphological and appearance traits for variety
identiication are size, color, shape, and seed coat texture or appearance. Seed coat surface may vary from
smooth and glossy to dull or rough, with different irregularities including pitting, grooves, and other types
of sculpturing. Hilum shape, size, and position can be very helpful in narrowing the range of varieties to
be considered. Fortunately, seed morphology is among the most stable of all plant features and is thus
an important taxonomic tool for varietal identiication. However, dificulties in identiication may still be
encountered, especially for closely related varieties. One way to overcome these dificulties is by the use of
scanning electron microscopy, although this method is not used commercially. While examinations by the
naked eye or light microscope focus on apparent color, shape and size details, iner morphological details
and features can be explored using scanning electron microscopy, especially seed coat features which are
known to be excellent taxonomic characters (Moro et al., 2001; Zeng et al., 2004). For more details, refer
to the AOSA Cultivar Purity Testing Handbook.
CHEMICAL (QuICk) TESTS
Quick tests, also referred to as rapid chemical identiication techniques (Payne, 1993), are a group of rapid
tests used to distinguish varieties based on differential seed or seedling reactions to exogenous physical
agents. Some quick tests rely on reactions of different enzymes (e.g., peroxidase) in the seed of different
varieties. Others rely on chemical compounds to highlight or clarify various features of the seed which are
not readily visible otherwise, as in the case of the potassium hydroxide and hydrochloric acid tests. Still
others use special lighting features (e.g., luorescent light) to help distinguish chemical compounds present
in the seed or seedling of various varieties, as in the case of annual ryegrass.
In addition to being rapid, quick (chemical) tests are relatively simple to conduct, and inexpensive.
They are generally used in conjunction with other tests to help assure positive identiication of a variety.
Among the quick tests are the following.
Copper Sulfate-Ammonia Test for Sweetclover (
Melilotus
spp.)
This method was irst described by Elekes and Elekes (1972) to distinguish seeds of white sweetclover
from yellow sweetclover, if the pods have been removed. If seeds are still in the pod, the two species can be
easily distinguished by pod ribs that form a mesh in the case of white sweetclover and are cross wrinkled
for yellow sweetclover (
Melilotus oficinalis
). The copper sulfate-ammonia test is speciied by the AOSA
Rules for determining the percentage of yellow sweetclover in a mixture of yellow and white sweetclover.
Refer to AOSA rules and AOSA Cultivar Purity Testing Handbook.
