Oct 20th 2005Economist Magazine
A banana bank is safeguarding the future of the crop
BANANAS, like their cousins, the tropical staples cassava and taro, have a characteristic that makes them ideal food. They have no seeds. Unfortunately, the same characteristic means that it is fiendishly difficult to breed better bananas. This is
an important task, as bananas are threatened by new kinds of pests and diseases. Furthermore, because bananas are clones, whole plantations could be devastated by such an attack.
This week, Leuven in northern Belgium was celebrating its unlikely role as the world's banana capital. The Catholic University of Leuven hosts the world's largest collection of banana diversity. Over the past 20 years, some 1,175 different kinds of banana have been carefully nurtured as tiny plants growing in test tubes. This in-vitro storage is expensive, because even when kept in cooler, darker and less nutritious conditions than normal, banana plants still outgrow their test tubes every few months. The plants had to be cut back and replanted, which took skilled labour.
Researchers at the university have now developed ways of deep-freezing banana samples. They have demonstrated that, after five years of being plunged into liquid nitrogen, banana cell suspensions can be recovered and turned into growing plants.
The most successful methods for improving the banana through genetic engineering rely on the availability of embryonic cell suspensions. Getting these is tricky, but the researchers hope that cryopreservation—that is, deep-freezing at extremely low temperatures—will preserve them indefinitely, once they have been obtained. As part of an agreement signed this week with the International Plant Genetic Resources Institute, the university will train scientists from developing countries in in-vitro and cryogenic techniques.
Breeding better bananas is important because bananas are so vulnerable to disease. In the 1950s, commercial plantations all grew one variety of banana, called Gros Michel. It was, by all accounts, a superior-tasting fruit to today's supermarket stocks of the Cavendish variety. The Gros Michel banana still grows in the more remote parts of Uganda and Jamaica. Elsewhere, it was wiped out by Panama disease, a wilt caused by a fungus called fusarium. This devastated the large commercial plantations that fed the export trade.
In 1992, the disease mutated into a form that is able to attack the Cavendish variety. Plantations in Malaysia were wiped out. At present, the disease is confined to Asia, but experts fear that it is only a matter of time before it reaches Latin America and the Caribbean.
Creating disease-resistant hybrids is thus a matter of some urgency. In addition to the traditional varieties, generated by natural mutations, a few such strains have been created by transferring genes directly from one variety to another. These are currently being tested in Uganda and Tanzania. It may prove possible to create a tasty banana that is resistant to Panama disease. Those who depend on bananas will hope the researchers do not slip up.
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