Front Range Seed Analysts
1994 Seed Forum Volume 8 Number 2
Dormancy in Seeds of Annual Grain Crops
by Arnold Larsen
An important method of survival evolved by most plant species is the ability to select germination conditions that provide new seedlings with the best chances of growth. This ability is provided by dormancy mechanisms located within seeds. Dormancy yields to favorable environmental conditions or time. In the domestication of most annual species harvested for their seeds, plant breeders try to eliminate or modify the influence of dormancy mechanisms so that the farmer is in control of when and where the seeds germinate. For the most part, plant breeders are successful; however, under maturation conditions where seeds develop to their fullest potential, sume latent dormancy mechanisms become established which will once again give to the seeds control over germination. This reestablishment of germination control in seeds of domesticated species has occurred in wheat, barley, proso millet, oats, crambe and several other annual crops. Dormancy in seed is expressed by failure to germinate, delayed germination, or germination over an extended period of time (like all summer).
It is now documented that several farmers had suffered crop failures by planting seed lots that were dormant but not reported as such on the seed label. The problem arises when seed dealers and sales people are reluctant to sell seed with a label that includes a dormancy percentage in the viability statement. Many seed analysts also prefer reporting all viability in terms of germination in response to the pressures from the seed industry and the extra labor involved in making this determination.
When all the viable seeds do not germinate by prescribed AOSA
pprocedures, the remaining seeds not germinated are to be tested for viability
by the tetrazolium test or other means. Those testing positive for
viability are to be reported as "dormant." Then the total viability
is the sum of the germination and dormant percentages. To reduce
analytical time and to meet with the approval of the seed marketing people,
seed analysts will perform extensive research in an effort to find a procedure
that will make all viable seeds germinate regardless of the depth of dormancy
they may possess. When they discover such a procedure, they present
a rule proposal to the AOSA membership requesting a rule change which inserts
the new procedure. Quite often these are accepted and seeds of the
crop kind in question will no longer have dormant seed reported regardless
of how deep the dormancy is. In support of this action there are
two dangerous generalizations:
1. Viable seeds that do not germinate in the laboratory
will probably germinate in the field, and
2. Seeds that are dormant when tested in the laboratory
will probably not be dormant by planting time.
Both generalizations are flawed as evidenced by the crop failures that
have occurred.
Who is really responsible for these crop failures? Is it the seed producer, seed dealer, seed analyst, or farmer? The seed with a high degree of dormancy is probably high in other aspects of quality so the seed producer has done a good job. The seed dealer and farmer simply believe what they are told or can read on a seed test report so they are not responsible out of naivety. It is the seed analyst who determines the factors that express seed quality and makes measurements of them. This information is supplied to all concerned who believe that the seed analyst has taken full inventory of all that is ultimately improtant to the production of a crop from that seed. One factor often overlooked is reporting dormancy.
The seed analyst should evaluate the quality of the seed as it is when the seed sample is received and should not anticipate what it will be at planting time. If at the time of testing in the laboratory, some resistance to germination is found that is caused by a dormancy mechanism, that fact is valuable information for everyone. The seed lot must be monitored regularly until resistance is diminished to assure that there will be no dormancy induced crop failures after planting.
People must stop developing seed testing procedures that bypass dormancy mechanisms if there is a possibility that dormancy can cause a crop failure. AOSA members must be cautious about using a seed dormancy reducing procedure if that procedure is associated only with the submitted seed sample and not with the entire seed lot. Dormancy is an important quality factor and should be reported. We must stop equating viability with germiantion for in doing so great financial damage can be done to unsuspecting growers.