Breaking dormancy in genebanks

Watch this video, in which scientists and genebank managers introduce dormancy strategies used by plants in the wild, and some of the measures that genebanks have adopted to break dormancy in the laboratory. The video mentions two different types of dormancy (physical dormancy and physiological dormancy). You will learn more about these later.

As you watch the video, think about how environmental conditions make dormancy a good strategy for seeds in nature, and how scientists at genebanks can mimic aspects of the natural world in order to give dormant seeds the best possible chance to germinate.

Download this video clip.Video player: Video 2: Breaking dormancy
The image shows a technician at the International Institute for Tropical Agriculture using a scalpel to break the seed coat of a legume seed.
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Transcript: Video 2: Breaking dormancy

Narration:
Plants in the wild have developed various strategies to stop their seeds from germinating. This keeps the seed safe until conditions are optimal for survival. So for scientists in genebanks, the key to breaking dormancy is to assemble evidence about the plant and its natural environment.
Fiona Hay:
Seed dormancy is a property of the seeds, which means that they're not able to germinate even though the conditions are right for germination in terms of water availability and temperature.
Narration:
Wild plants adopt dormancy because it brings some advantage to their offspring.
Fiona Hay:
It exists in nature in order to spread the germination of seeds, over time, and in space, so that not all the seeds would come up at once. For the genebank, what it means is that they might have to apply a dormancy-breaking procedure as part of their viability testing.
Narration:
IRRI’s collection includes almost all the wild relatives of rice.
Arma Kristal Pabro:
Rice wild relatives, they are like treasure troves of genetic diversity in the rice genome, so most of them will have beneficial genes that are can be incorporated in our cultivated rice, like pest resistance or resistance to environmental stresses.
Narration:
IRRI’s wild rice accessions have a diversity of desirable traits. But alongside these traits comes seed dormancy.
Arma Kristal Pabro:
Seed dormancy in wild rice is an intrinsic characteristic of the seed. Since these are wild materials that are found in forests or secluded areas, they have that trait of seed dormancy in their natural habitat. So what we’re doing now, is we’re giving them the right environmental conditions for them to germinate as a seedling.
Fiona Hay:
In some of the wild species, rice has a weak physiological dormancy. And the way that we can overcome that is to apply an after-ripening treatment. So placing the dry seeds at a high temperature for a few days.
Arma Kristal Pabro:
We place the seeds in the oven at fifty degrees Celsius for seven days. But some species would take a longer time to break their dormancy.
Narration:
The high temperature and dry conditions release the dormancy. It’s a good choice for breaking physiological dormancy. Other types of dormancy must be broken in different ways.
Fiona Hay:
If it's a physical dormancy, then we do manual scarification in some way. So that might be taking a scalpel and actually chipping a little bit of the seed coat off the seed, so the seeds are able to imbibe and then germinate.
Narration:
Some legumes have impermeable seed coats, which prevent water from getting through.
Kafayat Falana:
For those seed lots that have not germinated, we need to scarify them, with the use of a scalpel to puncture the seed coat of the seed, so the seed is able to imbibe water for germination processes.
Narration:
Scarification in the lab mimics a seed-spreading mechanism in the wild.
Fiona Hay:
What might happen in nature is actually these seeds would, be eaten by an animal or a bird. And then the acid inside the stomach, that's what would be overcoming the seed coat barrier.
Narration:
Some species of wild rice use a thick seed coat as a different dormancy strategy. The seed coat imposes a physical constraint. The seeds are able to take up water, but their embryos are not able to break through the thick seed coat. This technician is releasing that constraint. But the tiny embryos may still need an extra boost from a plant growth hormone to help them germinate. In colder climates, some plants give their seeds the best chances of survival by delaying the reactions that lead to germination.
Fiona Hay:
It might be that in nature they would have to go through a couple of seasons, before they'd be able to germinate. So for example, it might need to go through a winter period before it would be able be able to germinate in the spring, when the environment's better. And so it needs to experience the cold temperatures and then the warming up, and then it would be able to germinate. So in our dormancy-breaking treatments, we have to short-circuit this. Um, and one way to do this might be to apply a chemical such as gibberelic acid, GA3. So this is often used to overcome physiological dormancy.
Narration:
Plant dormancy strategies vary, so for scientists in genebanks, the best dormancy-breaking procedure will be the one that targets the strategy of the particular species. By understanding the mechanisms and reasons for dormancy, you can increase your chances of breaking it.
End transcript: Video 2: Breaking dormancy
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Video 2: Breaking dormancy
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Please use the box to write your comments on what the scientists say. What dormancy strategies do plants adopt in the wild? What conditions in situ are they adapted for? And how do laboratory techniques set out to mimic these conditions in the genebank? You should spend up to ten minutes on this. If your reflections on the video raise any questions, please post them on the Forum, where the course moderators will be able to help you.

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Discussion

Fiona Hay explains that dormancy is a strategy used by plants to spread the germination of seeds over space and time.

One example of spreading germination over space is legumes with a thick coat. An animal eats the seeds, and the seed coat is abraded, but not fully digested, inside the animal’s digestive tract. This breaks the dormancy. Meanwhile, the animal may have moved a long distance from the parent plant before excreting the seeds, now germination-ready. To overcome this kind of dormancy in the lab, scientists may use a scalpel to break the seed coat.

One example of seeds spreading germination over time is found in climates where one season is more conducive to germination than others. In temperate climates, dormancy allows seeds to delay germination over the winter, and to germinate in spring when conditions are better. To overcome this kind of dormancy in the lab, scientists may use either temperature changes or chemicals that resemble the plant hormones that would naturally be produced in the spring.

Dormancy

Changes in dormancy over time