If you like bananas, you probably eat a lot of clones.
That’s because all bananas are clones -- or at least, Cavendish bananas are, and they’re
the cultivar, or variety, of banana that most people eat. They’re genetically identical
to one another.
And they’re also all in danger of being wiped out by a fungus.
Cultivated bananas reproduce asexually, through a process known as parthenogenesis,
which literally means “virgin birth.”
Most plants have male and female flower-parts and seeds, that are pollinated with
the help of things like the wind, or bees. Pollination is the plant version of getting it on.
There are ways to create new banana cultivars if you pollinate them by hand, but it often fails,
and even when it does work it’s hard to know if your new banana will look good,
taste good, and be easy to grow.
So most bananas live a chaste life: if you’re a banana farmer, you get more banana plants
by cutting off a piece of the stem of an existing banana plant, and sticking it in the ground.
That plant then matures, blooms with potentially more than three hundred bananas, and then dies. Because they’re all the same, they’re super vulnerable to disease. There’s no
chance that one banana plant will happen to have a gene that makes it resistant
So if a parasite or a fungus can kill one banana, it could potentially kill every
banana of that type -- something that’s happened before.
Back in 2013, we here at SciShow talked about how the Gros Michel banana, which was bigger,
sweeter, and hardier than the Cavendish, went virtually extinct in the 1950s.
The culprit was a highly infectious fungus we called Panama Disease. In the space of
about ten years, Panama Disease reduced the Gros Michel from the world’s most popular
fruit, to just another weird thing your grandparents talk about that nobody else remembers.
And the banana industry would have died with the Gros Michel if it weren’t for the last
minute switch to the Cavendish. While it wasn’t as big and it didn’t taste the same as the
Gros Michel, the Cavendish was immune to Panama Disease.
At least, the type of Panama Disease that was around at the time.
In 2013, we also told you that a new strain of Panama Disease had emerged that could
infect the Cavendish. But that it would probably be fine!
Infected fields were being quarantined, scientists were working on developing a new kind of Cavendish
that could resist the new disease, and hey! We had the lessons of history! We weren’t
gonna let what happened to the Gros Michel just happen again, right?
So...here’s an update on /that/ story.
According to a study published in November in the journal PLOS Pathogens, this new strain
of Panama Disease, known as “Tropical Race 4” or just “TR4,” is spreading.
It originated in northern Australia, and, the last time we talked about this, it was
also in Southeast Asia and southern China. Since then, the researchers note, TR4 has
reached the Middle East, through Jordan and Lebanon, as well as Africa, through Mozambique.
TR4 in Africa is especially concerning because bananas in many parts of Africa, including
Mozambique, are not just a tasty treat. They’re a staple crop, and a major component of national
food security.
Even worse, it seems likely that TR4 could also infect other varieties of African banana,
many of which are grown as subsistence crops by rural families.
What makes TR4 so dangerous?
It’s caused by a fungus that spreads through soil. If you didn’t think dirt could carry
disease: it can, and when it does, it’s bad. TR4 spreads through the dirt and infects
plants via their root systems.
Worse, it produces chlamydospores, or “resting spores,” which can lie dormant in the soil
for decades. So just destroying an infected crop won’t solve the problem. Once soil
has been infected, it can’t be used for growing that kind of banana anymore at all
like maybe forever
And TR4 is so infectious that even a single clump of dirt lodged in the tread of your shoes would be enough to carry the disease to a new plantation.
So far, it hasn’t reached Central or South America,
which produce more bananas for export than anywhere else in the world.
But it probably can’t be kept out forever.
All told, it’s looking more and more likely that the Cavendish is going to go the way of the Gros Michel.
The questions now are: when?
and: will we develop a new type of banana that can replace it in time?
Either way, if you really like bananas …
you might want to enjoy them now, while you still can.
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And now, if you’ll excuse me,
I gotta go fill up my banana tank.