About four million tons of bananas are imported into the EU each year. A fungal disease is now threatening banana plantations, and plant breeders have not yet succeeded in developing resistant cultivars. Many hope that genetic engineering can offer a solution. At this point, such projects are still only in the greenhouse.
Monocultures offer the perfect conditions for the spreading of pests and diseases. In this respect, bananas are no different from any other crop.
Back in the 50s, the most common banana variety, Gros Michel, was completely wiped-out by what was known as Panama disease. This disease was caused by the fungus Fusarium oxysporum, also called fusarium wilt. Gros Michel was replaced by a resistant southern Chinese variety called Cavendish.
Genetically uniform bananas are defenseless to fungal diseases.
For the last thirty years a new disease has been becoming more and more widespread. The disease is called Black Sigatoka. Right now, the only way to treat this new disease is by applying massive doses of fungicides – a practice which is losing effectiveness as the fungus is becoming more resistant. In several regions the disease can cut banana yield in half, leading farmers to spray their plantations up to fifty times a year. This practice endangers the environment and the health of plantation workers.
Black Sigatoka isn’t only threatening the Cavendish bananas that are popular in Europe and North America. It also affects local varieties that are popular in Asia, Africa and Latin America. These include starchy plantains, prepared similarly to potatoes, which are a staple food in many poorer communities in the Third World.
Disease defense: Bananas lack genetic diversity
Monocultures and Black Sigatoka aren’t the only reasons why bananas are in trouble. Cultivated bananas are known as pathenocarpic, which means they can form fruit without ever having been fertilised. Rather than forming seeds, bananas reproduce by forming side-shoots and suckers. This means that the gene pool of bananas never really changes over the generations. This is a major restriction to breeding possibilities: all efforts to introduce fungus resistance to Cavendish bananas through conventional breeding methods have failed.
Many banana producers hope to save Cavendish bananas with the help of genetic engineering. This technique could finally be able to provide popular Cavendish bananas with resistance to Black Sigatoka.
Last year a group of scientists announced that they would completely sequence the banana genome. They intend to focus particularly on banana varieties found in nature. Wild bananas can reproduce by seeds and are constantly confronted with fungi and other pathogens. Sequencing the genome should enable researchers to discover resistance genes that could be transferred to high-yielding, seedless varieties.
Crop improvement efforts with bananas have been going on for quite some time. Researchers in Belgium, in cooperation with the INIBAP-Network, have been working for years to develop improved banana cultivars using conventional breeding methods and genetic engineering. Leuven University set up a banana archive comprised of 1200 banana varieties from all over the world.
Resistance genes from various plants including onions and dahlias were introduced into plantains, primarily with the goal of developing resistant plantain cultivars for the Third World.
The resulting genetically modified plantains exhibit resistance to the fungus in greenhouses. But before they can be released for use, some toxicological tests still need to be carried out.
If the breeding of resistant plantains succeeds – potentially with the aid of genetic engineering – it would be a contribution to food security in many tropical countries. Cutting back on fungicide spraying would also be an improvement for the environment and for the health of farm workers. Another important factor is the price of fungicides: many small farmers can’t afford to frequently spray against Black Sigatoka.
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