Agriculture Reference
In-Depth Information
Perhaps the most common cold test technique is the tray method in which the seed is planted on Kimpak or
other appropriate germination medium and then covered with a layer of soil (Fig. 8.6). Other corn cold tests
are conducted in soil between rolled paper towels stood upright in incubation chambers during cold expo-
sure while other tests are temporarily covered with a paper towel and placed in the incubator horizontally.
Soybean and dry edible beans may be cold tested in soil by the plastic “shoe box” method (Figure 8.7).
Several variables inluence standardization of cold test results. These include:
1. Conditions of substratum storage. Storage of wet soil under anaerobic conditions leads to an
increase in germination in the cold test or to erratic results (Nijenstein, 1995). The storage of air
dry soil does not enhance the discrimination of seed lots subjected to a cold test. Nijenstein (1995),
therefore, recommended that soils used in a cold test be stored wet and under aerobic conditions.
2. pH of the soil. The pH of the soil inluences the types of pathogens present in the soil and their
activity. Thus, pH should be controlled to assure repeatability of cold test results.
3. Soil type. Nijenstein (1986) showed that higher organic matter led to lower cold test results.
Presumably, this correlation is associated with increased biological activity of the microorgan-
isms. Further, since microorganisms grow and become established based on the chemistry and
type of crop grown, it is recommended that the soil used in a cold test come from the ield in which
the crop will be planted.
4. Moisture content of the substratum. Studies evaluating the inluence of moisture content on cold
test results demonstrate that germination percentages begin to decline when the soil moisture con-
tent is at or exceeds 60%. This may be because fungal activity is enhanced at these soil moisture
contents.
5. Type of substratum. Because soils contain biological microorganisms, it is dificult to standardize
a cold test. Some have attempted to use sterile media such as sterilized soil or sand, paper towels,
and vermiculite to overcome this dificulty. However, numerous studies have demonstrated that
effective cold tests must use unsterilized soil instead of sterile media (Fuchs, 1988; Loefler et al.,
1985; Bruggink et al., 1991). Studies examining this relationship have documented the importance
of soil pathogens in the success of the test (Nijenstein, 1986; Svien and Isely, 1955; Clark, 1954).
The pathogenicity of the soil can be enhanced by adding nutrient sources such as sugar or ground
seeds to the soil medium.
6. Temperature and duration of the cold test. The temperature of the cold test can be another variable.
Below 6°C, imbibitional chilling injury depresses germination results. Further, as the temperature
decreases below 10°C, fungal activity declines. The effect of the variety may also be important.
Some varieties are more cold tolerant than others, thereby providing higher germination results
in a cold test of seed lots of equal quality. The duration of the test represents another variable.
Cold test periods that are too brief fail to allow the pathogens to become established and culmi-
nate in higher germination values. Those that are too long eventually lead to total suppression of
germination.
7. Seed treatment. The type of fungicide applied to seeds can affect cold test results. This may be due
to differences in control of differing pathogens, whether the fungicide acts on contact or systemi-
cally, the amount of active ingredient applied to the seed, the rate of diffusion of the fungicide into
the soil, and the rate at which it dissipates in activity.
