Demise of the Clones

FOOD

A fungus that threatens the world’s most popular fruit is spreading. Could this be the end of bananas? (SciShow)

Use our resources to learn more about bananas and other fresh fruits and vegetables.

Teachers, scroll down for a quick list of key resources in our Teachers’ Toolkit.

Bananas are the world’s biggest berries, and grow on the world’s largest herb! (Herbaceous plants, unlike trees or shrubs, do not have a woody stem above ground.) Cavendish bananas like these are the most popular fruit in the world. Photograph by Rebecca Hale, National Geographic

Bananas are the world’s biggest berries, and grow on the world’s largest herb!  Cavendish bananas like these are the most popular fruit in the world.
Photograph by Rebecca Hale, National Geographic

Discussion Ideas

  • According to the 5-minute SciShow video, the Cavendish bananas we see in the store are actually clones. What are clones?
    • A clone is a cell or group of cells that is genetically identical to its ancestor. The DNA of every Cavendish banana is exactly the same as every other Cavendish banana.

 

  • Why are clones highly vulnerable to disease?
    • Absolutely no genetic variation. According to the video (cue up to about 1:05), “there’s no chance that one banana plant will have a gene that makes it resistant” to a disease. “If a parasite or fungus can kill one banana, it can potentially kill every banana of that type.”

 

The Gros Michel, or “Big Mike,” had a slipperier peel than the Cavendish. Suddenly, all those vaudeville banana-peel gags make sense. Photograph by Jeanne Modderman, National Geographic  

The Gros Michel, or “Big Mike,” had a slipperier peel than the Cavendish. Suddenly, all those vaudeville banana-peel gags make sense.
Photograph by Jeanne Modderman, National Geographic

  • How do we know a single fungus (also, it should be noted, a clone) can wipe out an entire species of banana?
    • It’s happened before. Prior to the 1950s, the only banana most Americans were familiar with was the Gros Michel, a variety that is larger and fruitier than the bananas we know today. Like Cavendishes, Gros Michels were clones. When Panama disease infected the Gros Michel, the Gros Michel was virtually wiped out of the international market. (Enter the Cavendish.)

 

Map by Ordonez N, Seidl MF, Waalwijk C, Drenth A, Kilian A, Thomma BPHJ, et al., courtesy PLoS Pathogens. CC-BY-4.0.

This map shows the extent of Panama disease, which is killing the world’s most popular and profitable banana, the Cavendish. Explaining the legend: Panama disease is caused by a fungus, Fusarium oxysporum, and the virulent strain is known as Tropical Race 4, or TR4. DArTseq stands for Diversity Array Technology, a genome-sequencing technology geneticists used to identify TR4.
Map by Ordonez N, Seidl MF, Waalwijk C, Drenth A, Kilian A, Thomma BPHJ, et al., courtesy PLoS Pathogens. CC-BY-4.0.

 

  • Why is destroying an infected crop not a solution?
    • According to the video (cue up to about 3:13), TR4 is spread through soil, and once the soil has been infected, it can never again be used for growing Cavendish bananas. “The only way to get rid of TR4 is with fungicidal soil treatments that are so toxic and harmful to the environment that they’re prohibited pretty much everywhere.”

 

  • It’s only a matter of time before TR4 reaches the precious Cavendishes of the Americas. Why is this “especially concerning”?

 

  • Infestation of the American banana crop could be the end of our precious Cavendishes. Oh no! What will we put on our cereal? What will we cover with ice cream?
    • Another cultivar, probably. Cultivars are plants that have almost always been created by human activity—selecting desirable characteristics from related plants and carefully propagating them. Cavendishes themselves are cultivars, meaning they were carefully cultivated for desirable characteristics such as tiny seeds, thin skin, and resistance to rot.
      • Take a look at this cool poster for some banana cultivars grown on the Big Island of Hawaii. Some are yellow, some are green, some are red, some are ice cream. (Yes, it’s a real thing. Ice cream bananas are also called blue java bananas, and they supposedly taste like vanilla custard or ice cream.)
      • According to researchers, “developing new banana cultivars, however, requires major investments in research and development and the recognition of the banana as a global staple and cash crop (rather than an orphan crop) that supports the livelihoods of millions of small-holder farmers.”

 

  • What characteristics would you look for in a cultivar to replace the Cavendish? Think about taste, price, nutrition, the global shipping network, and agricultural requirements such as climate, soil conditions, and labor input.
    • Would your answers change if you were the owner of a banana plantation? How about if you were an entry-level worker on the plantation?
    • Would your answers change if you were a banana-importing country?
    • Would your answers change if you were a resident of a developing country who depended on bananas for nutrition?
    • Would your answers change if you were a Latin American farmer who wanted to break into the banana market? How about an Alaskan farmer?

 

TEACHERS’ TOOLKIT

SciShow: Bananas Are Losing the War on Fungus

Nat Geo: Fresh Fruits and Vegetables

Student Science: Banana threat: Attack of the clones

(extra credit!) PLoS Pathogens: Worse Comes to Worst: Bananas and Panama Disease—When Plant and Pathogen Clones Meet

(extra credit!) Annals of Botany: Domestication, Genomics and the Future for Banana

3 responses to “Demise of the Clones

  1. Pingback: What Did You Read in 2017? | Nat Geo Education Blog·

  2. Pingback: 14 Things We Learned This Week | Nat Geo Education Blog·

  3. Pingback: Australians Spent 50,000 Years Isolated from the Rest of Us | Nat Geo Education Blog·

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s