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Seed Coating
 The primary way of enhancing seed performance is through
the addition of chemicals to protect the seed from
pathogens. These are generally fungicides, although
insecticides and other protecting agents can also be
applied in this way.
Until recently, these chemicals
were applied mainly as a slurry that coated the seeds
and then was dried. Disadvantages of this method are
that it is difficult to get a uniform coating of the
material on the seed and much of the material can be
rubbed off the seed during transport and handling. This
is wasteful of the chemicals, is hazardous for the
workers planting the seeds, and in some countries,
including the U.S., requires the disposal of the seed
bags as a hazardous waste.
In recent years, film-coating
methods have been developed to overcome these problems.
In film coating, the chemicals are applied in a polymer
that is sprayed on the seeds as they fall though a
specialized machine. The polymer is rapidly dried, so
that the seeds emerge with a complete, dry polymeric
coating.
This coating does not rub off the seeds,
greatly reducing worker exposure and waste. In addition,
colors can be added to the polymers to code different
varieties or seed lots. Large-scale units capable of
treating large quantities of seeds have been developed,
making it feasible to treat high-volume agronomic crops
by this method as well.
Some novel applications have also been developed using
the film coating method. For example, artificial
polymers have been developed that exhibit
temperature-sensitive permeability to water. These
polymers are permeable to water at warm temperatures,
but not at cool temperatures.
Seeds coated with these
polymers will not imbibe water – that is, absorb water
and swell - if the temperature is below the set point of
the polymer, potentially protecting the seed from
chilling injury or germinating in an unfavorable
environment.
The coatings are also being used to delay
germination after planting, such as for timing the
emergence of parental lines at different times to ensure
synchronous flowering for hybrid seed production. A
starch-based biopolymer is also being used in film
coating to slow water uptake and alleviate chilling
injury.
Additional
resources:
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