Drying seeds in genebanks

In module 3, you learned that international genebanks have devoted quite a lot of research to finding the best methods for drying seeds. You were introduced to the scientific evidence in favor of initially drying rice seeds at high temperature, before continue to dry according to the Genebank Standards. Here is a reminder of the evidence from trials at the International Rice Research Institute (IRRI) that you first saw in the section of module 3 entitled ‘Dried to perfection’.

The graph shows declines in viability of rice associated with different initial drying temperatures. The x axis shows the storage period (days). The y axis shows percentage germination. The decline in viability approximates to an S-shaped seed survival curve like the one introduced in module 2. The decline in viability for samples initially dried at fifteen degrees is steepest, and results in the earliest loss of viability (at about twelve days). The decline in viability for seeds dried at forty-five degrees is the least steep, showing viability is maintained for longest, dropping to zero at about twenty-seven days. Even drying at the very high temperature of sixty degrees results in viabilty dropping off at about eighteen days: a better result than drying at fifteen degrees.
Figure 13: benefits of drying at a higher temperature

These results suggest that for seeds that have not dried sufficiently on the parent plant, it is possible to obtain improvements in longevity – often by many percentage points. These improvements in longevity were enough to convince IRRI to make changes to their drying procedures.

The next video tells the story of the research behind those graphs, in the words of some of the scientists who were involved. Fiona Hay, one of the pioneering scientists conducting the first research at IRRI, discusses the initial investigation on rice. Olaniyi Oyatomi and Sola Owoborode take up the story of how these findings were rolled out to legume crops at IITA. You will see the two-stage drying system adopted by IRRI as a result of these investigations, and hear scientists talk about the benefits two-stage drying has brought. As you watch, think about how scientific investigations like this can translate into improvements in genebank procedures.

Download this video clip.Video player: Video 4: two stage drying
The image shows a technician moving a new accession of rice into the International Rice Research Institute’s high temperature drying room.
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Transcript: Video 4: two stage drying

Narration:
Growing in the field, seeds are subject to uncertainties of weather and climate. Sometimes, gene banks need to compensate for poor drying in the field. But do standard drying procedures give seeds the best chance of longevity?
Fiona Hay:
So in the Genebank Standards, um, we have a range of conditions that can be used for drying the seeds for gene bank storage. So you can dry seeds between five and 20 degrees C and 10 to 25% relative humidity. In reality, many gene banks have a, a purpose-built drying room. Um, and that's set at 15 degrees C and 15% RH.
Narration:
Every day, the seeds are shaken to ensure they dry evenly. Is there anything else that can be done to improve the drying process? A team of scientists at IRRI gene bank decided to examine the evidence.
Fiona Hay:
we looked at this, these drying conditions to see if they really were optimal for drying rice seeds before gene bank storage. Um, and what we actually found was that it was better to initially dry the seeds, um, at a higher temperature, before we then dried them down to equilibrium, for the moisture content the optimum moisture content for long-term storage in the genebank. So at IRRI now they do have this two-phase drying.
Narration:
When seeds arrive at IRRI, samples are tested for water activity, so the scientists can discover how dry they are after harvest. The seeds are also checked in to the genebank’s information system.
Marionette Alana:
Using our database, so we use our barcoding system, and we receive all the samples. And then we put it in first stage drying.
Narration:
After three to four days’ drying at high temperature, the seeds are transferred to a separate drying room, where they continue to dry at lower temperature. In IRRI this is known as “second stage drying”.
Fiona Hay:
We've done research on rice and some other species, where we've actually found that it's better for the subsequent longevity of the seeds if we initially dry the seeds at a higher temperature. Um, so about 30, 40 degrees C and then put them in the drying room at a, at the 15, um, degrees C for the final equilibrium drying. Um, and this seems to work to extend the longevity of the seeds when we put them into gene bank storage.
Narration:
The scientists wanted to find out whether other crops could benefit from two-stage drying. And IITA has a wide variety of legume crops to investigate.
Sola Owoborode:
My PhD research was focused on improving and ensuring seed longevity by exploring warmer temperature drying for soybean seeds.
Olaniyi Oyotomi:
An example of a crop in which we have, uh, increased longevity is Bambara groundnut. Bambara groundnut happens to be an oil crop that has a short, lifespan. We carried out an experiment to monitor how the longevity can be extended, which has been proved to improve longevity in rice, for example. So we tried to use the same method of, uh, drying the seed at a higher temperature of 40 degrees, 45 degrees as against normal, uh, uh, drying at 17 degrees. This has extended the longevity of Bambara groundnut specifically, uh, better than before.
Sola Owoborode:
From my findings, drying soybean seed at warmer temperature was, um, beneficial. The benefit of drying at warmer temperature extends the length of the storage period of the seed conserved in the genebank.
Narration:
Back at IRRI, two-stage drying has proved its worth. Alongside other innovations, such the automatic seed sorting machine, initial drying at high temperature has delivered real improvements to their quality management.
Marionette Alana:
With the use of the two-stage drying and the automatic seed sorter, we were able to reduce the time from processing to storage. Previously, it would take us around one year to finish processing all the harvest that we collect here, but with the help of these technologies, we were able to reduce it in less than six months. These technologies doesn’t just help us in minimizing the processing time, but it also helps us in maintaining the high quality of seeds.
End transcript: Video 4: two stage drying
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Video 4: two stage drying
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Discussion

In IRRI’s two-stage drying, once seeds have been checked into the database, they are dried for the first few days at a temperature of around 30°C. Then they are moved into a second drying room, where they reach equilibrium at a lower temperature. The story of the research is interesting in itself, because it shows how a hypothesis made about one crop (rice) can then be tested in other crops (Bambara groundnut and soybean). Successful scientific investigations like this provide an evidence-base to support improvements to genebank procedures.

The seed information database

My genebank and me