Coconut embryos cross the Atlantic to safe new home
Brazil and the International Coconut Genetic Resources Network (COGENT) recently decided to establish a regional coconut genebank in Brazil, to serve Latin America and the Caribbean. Implementing the decision, however, was anything but straightforward.
- Seednuts, the result of controlled pollination, start their journey to Brazil. Credit: S.R.R. Ramos/Embrapa
A foil packet in a conventional genebank can contain thousands of individual seeds. Coconuts are seeds too, and also need safeguarding, but they are much too big to be stored in a genebank. What's more, they cannot be dried for long-term storage, even if there were room. That makes field genebanks necessary. But establishing safety duplicate collections around the world raises problems. The obvious solution is to move the mature seednuts, produced from carefully hand-pollinated flowers to preserve their genetic identity. The problem is that in addition to being big and bulky, they could carry diseases. Years ago Bioversity and its partners drew up guidelines for the safe international movement of coconut genetic diversity, and since then have been trying to promote the use of less risky methods, such as moving just the embryos found within the seeds.
The embryo of a coconut is slightly bigger than a grain of wheat, and sits beneath one of the three eyes in the shell. It can be quite easily cut out with a plug of coconut meat around it and then grown into a seedling using standard tissue-culture techniques.
"That was OK for some transfers," says Luz Maria George, Coordinator of COGENT, referring to earlier embryo culture efforts, "and the researchers optimized the procedures, but there was no large-scale success."
George and the manager of the new regional genebank in Brazil, Semïramis Ramalho Ramos, got together to plan how to make the most of Brazil's very limited budget for establishing the new facility. With individual seednuts costing US$4 for dwarf varieties and US$14 for talls (because pollination is so much more difficult; see 'Raising a new generation of coconut trees,' Bioversity Annual Report 2006, p. 20) a lot of the funds would have gone on the raw material.
"We decided to use embryo transfer, and we planned very carefully to anticipate all the potential problems," George said. That meant obtaining no fewer than nine official documents for each batch of embryos and several others that would be helpful. A crucial concern for Brazil was lethal yellowing disease, which is not present in the country. All the donor trees had to be certified as free of the disease.
It turned out to be cheaper to fly Ramalho Ramos and Ana da Silva Lédo, a tissue culture expert, to Côte d'Ivoire, rather than relying on a courier firm to deliver the embryos. This would also avoid the distressing possibility of paying all that money for the seednuts, collecting the embryos and then having them accidentally forgotten out in the sun to shrivel and die. With planning reminiscent of a military campaign the two scientists arrived at the field genebank, bringing with them sterilized supplies from Brazil, and proceeded to process nuts every day for a week. There are scores of steps, from disinfecting the exterior of the seednuts to packing the excised embryos in insulated boxes. As George said, "It isn't rocket science, but you have to implement it properly."
They ended up with more than 2300 plugs from 12 varieties, the numbers calculated to allow for a level of embryo failure based on previous efforts that would still leave more than enough individuals of each variety to populate the field genebank.
Back in Brazil, the Ministry of Agriculture had to inspect the plugs containing the embryos before any further work could be done. With that certificate in hand the embryos were cut from the plugs and incubated in a growth medium. Of the 2141 embryos that arrived intact and could be processed further, just 32 (1.4%) were contaminated with fungi, while 354 (15.3%) suffered bacterial contamination. These rates are low, compared with previous studies, showing that the meticulous procedures were effective, but they also indicate that a focus on bacterial contamination is likely to be valuable for future research.
More assessments will take place as time goes on, from the survival rate of the excised embryos to the successful establishment of the trees in the field genebank. These data are crucial to the future use of embryo transfer for coconut, a fact recognized by the Global Crop Diversity Trust, which funded a training and research workshop in the Philippines in December 2008. The workshop enabled participants to discuss the practical aspects of embryo transfer and to share results in order to come up with recommendations for how best to implement the protocol to improve the chances of success.
The Trust is keen to see a rationalized system put in place for the long-term conservation of coconut using efficient and safe techniques for moving coconut diversity around. "The workshop showed that neglecting one small point in the protocol can result in a very expensive loss of germplasm. There is no reason why that has to happen," said Charlotte Lusty, coordinator of the Trust's coconut project. More seednuts are being produced in Côte d'Ivoire, and COGENT has invited applications from regional genebanks to host some of the varieties as a safety duplicate and to further refine the embryo-transfer techniques.
"We need a little more research to make the protocol even more robust," said George. "And the technique needs to be implemented properly and meticulously." To that end, a proposal has been put to the Rural Development Administration in Korea, which is fast becoming a powerhouse of tissue culture and cryopreservation in the region, to train researchers in the correct techniques and to create a global collection of cryopreserved coconut diversity.
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