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Seed Priming: Speeding Up The Germination Process

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Seed Priming: Speeding Up The Germination Process

USDA-ARS

Imagine you are the owner of a greenhouse which produces bedding plants. A customer orders 100 flats of begonia seedlings and wants to pick them up in a month. You begin to panic, as begonia seeds are sometimes slow to germinate and occasionally germinate unevenly.

What Is Seed Priming?

Your answer may be to obtain primed seeds. Seed priming is used by seed producers and growers to control germination. Mainly, seed priming is used to shorten germination time, which, as in the case of the begonias, is often desirable. The various seed priming processes have been carefully designed to allow for some of the early germination processes to take place, but not for the completion of full germination. Therefore, a grower can plant primed seed which has much of the germination process completed, and expect early emergence.

The process can also allow for more uniform, even germination of the treated seeds. It can also increase germination over a wider temperature range, and reduce disease incidence in seeds. In some plant species, priming is necessary, rather than merely desirable, in order to overcome seed dormancy.

How Does Seed Priming Work?

Seed priming allows for the regulation of the water content in the seed, either by soaking the seeds in water or in a solute; or, by exposing the seeds to water vapor. The seeds imbibe water for a predetermined time interval. After the time interval, the process is halted right before the first root, called the radicle, emerges from the seed. A high amount of water is needed for radicle emergence, so the priming process is ceased to prevent full germination from occurring. The primed seeds can then be dried and sown when ready.

You may be wondering why the seed doesn't dry out during the priming process, and become unable to germinate. If the process is properly controlled, the hydration treatment is stopped before the desiccation tolerance is lost. There is a limit for each plant species as to when the line between priming and pre-germination is crossed. Safe limits have been calculated as to the maximum length of time for which seeds can be primed. If the maximum length is exceeded, it can lead to seedling damage.

Seed Priming Methods

There are four common methods utilized for priming seeds: hydropriming, osmotic priming, solid matrix priming, and drum priming. Other methods are proprietary, which means they are trade secrets, or patented, so someone would have to pay to use those methods!
  • Hydropriming. Hydropriming is the simple soaking of seeds in water, although aerated distilled water is preferred. This process is especially useful in economically disadvantaged, arid crop growing areas.
  • Osmotic priming. Osmotic priming, also called osmopriming or osmoconditioning, is the soaking of seeds in solutions containing chemicals such as mannitol, potassium nitrate (KNO3), potassium chloride (KCl), polyethylene glycol (PEG), or sodium chloride (NaCl). Plant hormones, which control or affect various stages of seed germination, or beneficial microorganisms (which help control fungal and bacterial disease) can be added to the osmopriming solutions.
  • Solid matrix priming. Solid matrix priming involves the incubation of seeds in a solid, insoluble matrix, such as vermiculite, diatomaceous earth, or another highly water absorbent polymer, with a limited amount of water, allowing for slow imbibition.
  • Drum priming. Seeds are hydrated by placing them in a rotating drum into which a controlled level of water vapor is released.

Who Benefits From Seed Priming?

Seed priming is most often used for high-value crop seeds, but the "steeping" process of hydropriming has been used in arid countries to help overcome soil deficiencies and improve crop production. The disadvantages to seed priming include the fact that primed seeds are difficult to store in some cases, as they need cool storage temperatures -- not to mention the fact that the process is a sometimes time-consuming extra bit of effort. However, in most cases, seed can be primed overnight, surface-dried, and sown the very next day. In cases such as the one involving begonias, outlined at the beginning of this article, seed priming can be a necessary and even simple part of growing plants.
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