WHEN bananas started to be widely exported in the 1870s,
they were an exotic treat. But by the 1950s the fruit (botanically, a herb, but
never mind) was a favorite of millions far from the tropics. Then Panama
disease struck. The soil fungus swept through Central and South America,
killing banana plants in its path. By the 1960s Gros Michel (Big Mike), the
variety accounting for virtually all exports, was close to extinction. The export
industry approached collapse.
Bananas are now the world’s most valuable fruit. Exports
rose from 11.9m tonnes in 2001 to 16.5m in 2012. Americans eat more bananas
than apples and oranges together. But once more the export industry is fighting
to survive—and this time, on two fronts.
First, Black Sigatoka, a disease which blackens leaves
and can halve yields, is showing resistance to the fungicide used to combat it.
It is normally controlled by spraying almost weekly, which increases growers’
costs considerably. Now growers in some places are having to increase dosage
substantially, suggesting that spraying could soon become not just pricey, but
ineffective. Second, Foc Tropical Race 4, a strain of Panama disease that
attacks the Cavendish, has struck in several countries. Central and South
America, which produce four-fifths of exports, have so far escaped. But “it’s
not a question of whether it will occur there,” says Gert Kema, a plant
pathologist at Wageningen University in the Netherlands. “It’s a question of
when.”
The race is now on to find a banana that is both
resistant to the two diseases and commercially viable. Consumers might turn
their noses up at pungent varieties. Thin-skinned ones would not survive weeks
in a ship’s hold. A candidate may be hidden in the Laboratory of Tropical Crop
Improvement in Leuven, Belgium, which houses a big collection of specimens of
bananas and plantains (close relatives that must be cooked before eating).
Modifying the Cavendish is another, perhaps quicker, approach. Scientists
at the UN and the International Atomic Energy Agency have bombarded plants with
gamma rays; three of the resulting mutants have shown resistance in the
laboratory to Black Sigatoka. And Musa acuminata malaccensis, a wild Asian fruit that is the
precursor of edible bananas, is thought to be resistant to Panama disease. A
hybrid Cavendish containing some of its genes has grown well in infected
ground. But in both cases, field tests are needed.
Cavendish, like other cultivated banana varieties, is
seedless and propagated by cuttings. That produces clones, which is efficient
for exporters, since the fruit are all similar in shape and size. But it also
means a single disease can threaten the entire crop—and the non-tropical
world’s banana supply. If the export industry is to have a long-term future, it
needs to diversify.
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