(Intro)

Hank: If you like bananas, you probably eat a lot of clones. Because all bananas are clones, or at least Cavendish bananas are, and they are the cultivar, or variety, of banana that most people eat. They're genetically identical to one another. And they are 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. And 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 is gonna look good, taste good, and be easy to grow. So most banana plants 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 plant and then sticking it in the ground.

That plant then matures, blooms with potentially more than 300 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 fungus can kill one banana, it could potentially kill every banana of that type, that's something that's happened before.

Back in 2013 we here at SciShow talked about 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 but 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 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 that 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 have 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 are 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 the soil has been infected it can’t be used for growing that kind of banana any more, at all, like maybe forever.

The only way to actually get rid of it is through fungicidal soil treatments which are so toxic and harmful to the environment that they’re prohibited pretty much everywhere. 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 gotten to 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 be able to develop a new type of banana to replace it in time? Either way, if you really like bananas you might want to enjoy them now while you still can.

Thanks for watching this episode of SciShow News and thanks especially to all of our patrons on Patreon, we want to make even more SciShow videos and you guys are helping us work toward that goal. If you want to help us keep making videos like this you can go to patreon.com/scishow. And now if you’ll excuse me, I gotta go fill up my banana tank.