A Threat of Bananas
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In the 1950s, Central
American commercial banana growers were facing the death of their most lucrative
product, the Gros Michel banana, known as Big Mike. And now it’s
happening again to Big Mike’s successor – the Cavendish.
With its easily
transported, thick-skinned and sweet-tasting fruit, the Gros Michel banana
plant dominated the plantations of Central America. United Fruit, the main
grower and exporter in South America at the time, mass-produced its bananas in
the most efficient way possible: it cloned shoots from the stems of plants
instead of growing plants from seeds, and cultivated them in densely packed
fields.
Unfortunately, these
conditions are also perfect for the spread of the fungus Fusarium
oxysporum f. sp. cubense, which attacks the plant’s roots and prevents it
from transporting water to the stem and leaves. The TR-1 strain of the fungus
was resistant to crop sprays and travelled around on boots or the tyres of
trucks, slowly infecting plantations across the region. In an attempt to escape
the fungus, farmers abandoned infected fields, flooded them and then
replanted crops somewhere else, often cutting down rainforest to do so.
Their efforts failed.
So, instead, they searched for a variety of banana that the fungus didn’t
affect. They found the Cavendish, as it was called, in the greenhouse of a
British duke. It wasn’t as well suited to shipping as the Gros Michel, but its
bananas tasted good enough to keep consumers happy. Most importantly, TR-1
didn’t seem to affect it. In a few years, United Fruit had saved itself from
bankruptcy by filling its plantations with thousands of the new plants, copying
the same monoculture growing conditions Gros Michel had thrived in.
While the operation was
a huge success for the Latin American industry, the Cavendish banana itself is
far from safe. In 2014, South East Asia, another major banana producer, exported
four million tons of Cavendish bananas. But, in 2015, its exports had
dropped by 46 percent thanks to a combination of another strain of the
fungus, TR-4, and bad weather.
Growing practices in
South East Asia haven’t helped matters. Growers can’t always afford the
expensive lab-based methods to clone plants from shoots without spreading the
disease. Also, they often aren’t strict enough about cleaning farm equipment
and quarantining infected fields. As a result, the fungus has spread to Australia,
the Middle East and Mozambique – and Latin America, heavily dependent on its
monoculture Cavendish crops, could easily be next.
Racing against the
inevitable, scientists are working on solving the problem by genetically
modifying the Cavendish with genes from TR-4-resistant banana species.
Researchers at the Queensland University of Technology have successfully grown
two kinds of modified plant which have remained resistant for three years so
far. But some experts think this is just a sophisticated version of the
same temporary solution the original Cavendish provided. If the new bananas are
planted in the same monocultures as the Cavendish and the Gros Michel before
it, the risk is that another strain of the disease may rise up to threaten the
modified plants too.---Take the Quiz---
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