Genebankers’ perspectives

Let’s revisit the two genebanks, IITA and IRRI. The next documentary explores what goes on while seeds develop in the field, and how seed scientists and genebank managers decide on the best time to harvest. The video tells the story of a seed’s early life, from flowering to threshing. By tracking this development carefully, the scientists can make a difference to the physiological quality of seeds when they enter the genebank.

As you watch, think about how the genebanks harness seeds’ developmental processes to maximize their longevity in storage.

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The image shows a still from the video: a technician harvesting rice. Check out the video transcript for more detailed video content.
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Transcript: Video 1: from field to genebank

Narration:
What happens to crops growing in the field will affect the longevity of the seeds once they enter the genebank. Let’s explore the seed’s life story a bit more. It starts with a flower, and a chance of fertilization.
Sola Owoborode:
This is a soybean plant at flowering stage. The color ranges from purple to white color, and soybeans are self-fertilizing crops, there is no cross-pollination.
Narration:
After fertilization, a series of transformations take place.
Fiona Hay:
So when we talk about seed development, we talk about three phases. So after fertilization, you get the first phase, which is where there’s cell differentiation, and embryogenesis. So the structures of the seed are forming.
Olaniyi Oyotomi:
The initial part of the seed development is that the embryo is formed, and then it’s attached to the walls of the uterus, as it may be for the type of crop or species.
Fiona Hay:
In the second stage we get cell expansion and dry matter accumulation. So dry matter is moving from the mother plant into the developing seeds. That’s when we see big increases in the dry weight of the seed.
Olaniyi Oyotomi:
Full mass maturity of the seeds signifies the end of the development of the seeds.
Narration:
At ‘mass maturity’, the dry weight of the seed reaches a plateau. It no longer needs nutrients from the parent plant. The connection between the seed and its parent plant becomes blocked.
Fiona Hay:
Because the vascular connection is now stopped, it’s blocked. What we also see then is that's when the seeds start to dry down to ambient conditions, so they start to equilibrate with the ambient humidity and the ambient temperature. And we call that last phase, at this point we call this the ‘maturation-drying phase’. And this maturation-drying phase is very important for the physiological quality of the seeds. So it's very important that we try and let the seeds on the plants go through this maturation-drying phase to get the maximum quality longevity of the seeds for the harvest.
Narration:
Changes taking place inside the seeds are reflected in changes to their external appearance.
Sola Owoborode:
This is a young soybean plant, with immature pods, they are still very fresh with immature pods and not yet ready for harvest. While over here, we have a matured soybean plant, with mature dry pods and the detachment of the leaves from the mother plant.
Olaniyi Oyotomi:
And the seeds start to signify with various signs of maturity like, the seed coat is formed and it becomes thickened. The color of the seed cover begins to change color to brown in cowpea, and then that signifies the end of maturity of the seeds, and at that time the seeds are ready for harvest.
Narration:
The signs to look out for depend on the species. This is rice.
Andres Godwin Sajise:
The best criteria to check when the materials are ready to harvest is your data on flowering. This will tell you what time the seeds have fertilized, and the process of maturity will start around thirty or even more number of days. Second is the ripeness, or the color of the seeds, should be uniform from the tip to the panicle base.
Narration:
Once the seeds have reached this level of maturity, the harvesters can move in. In legumes, too, there are physical changes to show seeds are ready for harvest.
Oladepo Adebowale:
These are cowpea plants. We have pods that are at pod filling stage, pods that are mature but not ready for harvesting, and we have mature pods, gone pale brown; and when you press, you’re going to hear it crack.
Narration:
These maize plants give different clues that they’re ready to harvest.
Olubiyi Adeyemi:
One of the determinants that we look at before harvesting maize, is we look at the color of the plant itself. Then we also look at the color of the cob, when the cob is brown. Then we also look out for when the silk detaches from the cob, which means the seeds must have dried.
Narration:
IRRI has twenty-three species of wild rice in its collection. These bring particular challenges for harvesting. The net bags are added very early, to get over the plants’ natural behavior.
Arma Kristal Pabro:
We bag the panicles after flowering because most of the wild rice species, they have highly shattering panicles. So we do the harvesting at around thirty days after bagging. We collect the seeds, using the net bags, because at maturity, the seeds would be falling off the panicles.
Narration:
These are cowpeas from IITA. They must be threshed soon after harvest while they’re still fresh. The seed covers are blown away, leaving behind the cleaned seeds, ready for genebank storage. At IRRI, the newly harvested rice must be threshed in ways that don’t damage the precious seeds.
Andres Godwin Sajise:
We have two ways of threshing the samples after harvest. First is the machine threshing for samples that are easy or intermediate to thresh. But we do hand threshing for the samples that have difficult thresh-ability. In this way we are getting good seed recovery and high quality seeds for our conservation.
End transcript: Video 1: from field to genebank
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Video 1: from field to genebank
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Discussion

If seeds are to maintain their viability during storage, they must first be at the right level of maturity when they arrive at the genebank. Fiona Hay and Olaniyi Oyotomi explain the developmental processes leading up to this optimum level of maturity. It takes a predictable number of days to complete the transformation, so genebankers keep careful records of the number of days after flowering. The parent plant gives visual signs as well. Sola Owoborode, Andres Godwin Sajise, Oladepo Adebowale and Olubiyi Adeyemi demonstrate the clues to look out for. Weather permitting, it is best to wait until the final stage of seed development, during which time seeds dry down to equilibrium with the surrounding air.

Conditions in the field

Conditions in the genebank