Agriculture Reference
In-Depth Information
Saturated Cold Test
In recent years, several modiications have been made to the cold test and have gained prominence, par-
ticularly in the seed corn industry. Such modiications have been made in the attempt to help standardize
cold test results by standardization of the methods and procedures under which they are performed. The
basic difference between the cold test and the saturated cold test is that in the latter the soil is maintained at
100% water holding capacity (saturated) for the duration of the test. As far back as the mid-1950s, Goodsell
et al. (1955) described a saturated cold test procedure for evaluating hybrid and inbred lines of corn. More
recently, Martin et al. (1988) described a cold test modiication used by analysts at Pioneer Hybrid in which
the seeds are placed embryo down on a thin layer of sandy-loam soil spread over wet germination paper
prechilled at 10°C. The saturated cold test evaluates seeds based on their response to three stress factors:
imbibitional chilling injury, attack by soilborne pathogens and limited O
2
availability. Consequently, the
saturated cold test is more stressful than any other test procedure. This test has been modiied by drying,
grinding, and screening the soil prior to uniform leveling with a template.
A towel is placed on a tray, with each end of the towel constantly in contact with water in a container
below the assembly. The assembly can then be covered by another towel or soil can be directly and evenly
spread over the wick towel. In either case, the soil is kept saturated by the wick towel which draws water
from the container below. After equilibrating the soil to the desired low temperature, seeds are planted on
top of the water-saturated soil and gently pressed, embryo-side down, to a depth of 1 mm into the soil. Seeds
should not be planted so deeply into the soil that they are completely deprived of oxygen. The whole assem-
bly is then placed in sealed carts and kept at the appropriate low temperature (usually 10°C) for the duration
of the test (usually 7 days). At the end of the test period, seeds and seedlings are evaluated for germination
percentage and number of normal and abnormal seedlings. More details about the cold test are described in
the 2009 AOSA Vigor Testing Handbook.
Controlled deterioration Test
Despite the advantages and simplicity of the accelerated aging test, its primary use has been limited to
large-seeded agronomic crops. The test has been less studied for small-seeded vegetable, lower, and turf
crops. When studies have been conducted, correlations with seed quality have been poor (Powell, 1995).
This has been attributed to a large variation in seed moisture content where small-seeded crops absorb
moisture rapidly and achieve maximum moisture content after only one day of aging.
To address the need for a small-seeded vigor test utilizing the principles of accelerated aging, Matthews
(1980) proposed the controlled deterioration test. This test functions by hydrating seeds on ilter paper to a
recommended moisture level (usually between 19 and 24%), placing the seeds in an aluminum foil packet
that is sealed and incubating the seeds at 45°C for 24 h in a water bath. Achieving the desired seed mois-
ture content before exposing the seeds to high temperature is the major limitation of this test (TeKrony
and Spears, 1978). Numerous studies have shown that this test correlates well with ield emergence and
storage potential (Powell and Matthews, 1981, 1984, 1985; Wang and Hampton, 1991; Bustamante et al.,
1984). One of the important and dificult aspects of this test is that seed moisture content must be precisely
controlled at the same level prior to sealing in the packet. Even minor differences of ± 1% can have major
effects on controlled deterioration results (Powell and Matthews, 1981). This means that minor adjust-
ments are often necessary in seed moisture content by either drying or rehydrating the seeds until the cor-
rect moisture content is achieved (Powell, 1995). To further improve this process, Hampton et al. (1992a)
recommended that a speciic amount of water be added directly to the foil packet containing the seeds. The
seeds then imbibe the water in the sealed packets which are equilibrated at 5°C for 24 h. Another approach
is to place the seeds in containers containing saturated salts to increase seed moisture content to the desired
moisture level (Jianhua and McDonald, 1996). More details about the controlled deterioration test are
described in the 2009 AOSA Vigor Testing Handbook.
