Saturday, November 12, 2016

Why are bananas so susceptible to diseases?

One of the most delicious fruits, specifically Cavendish bananas, is at risk. A fungus is spreading and it is out to get the Cavendish banana that is sold in North America and Europe. This disease is known as the Panama disease. Although this disease spreads slowly, it completely wipes out bananas where ever it goes. It is known as Tropical Race 4 or TR4 and it has been spread to China, Indonesia ,Southern Africa, and Asian countries such as Pakistan and Lebanon. Gert Kema examined the fungi from each of the locations where it had spread in order to identify strains of TR4 that infected the plants.

When cells copy, small variations in DNA occur as they reproduce and after a period of time it all adds up. Comparatively, TR4 works differently and does not produce these variations. As Kema gathered DNA samples from each of these locations, he found that each DNA sample was an exact match of each other. Surprisingly, he found that this is because each spore is a clone of the original fungus that invaded Taiwan. This study shows that each fungus is genetically identical. Some bananas could have resisted the fungi if small variations in the DNA occurred. But since the genes in all of the bananas and the disease were very similar, they could not resist the fungi. Cavendish bananas lack any diversity and are all planted together which is what sparked the disease to spread very easily. Scientist have tried to figure out how to stop the disease from spreading, but it is very difficult to do so. TR4 starts from the soil and grows long hyphae after attacking the plants roots. The long hyphae blocks the plants vascular system which reduces the amount of water it receives, eventually causing it to wilt. The fungus than continues to release spores into the soil, which is a main contributor to causing a wide variety of bananas to die as they are planted because once a plantation is infected, it will stay infected for decades. 
For now, scientists hope that they can develop bananas that are resistant to the fungus. But since bananas and TR4 lack genetic diversity on a tremendous scale, it will be very difficult to decrease the amount of bananas that are vulnerable to TR4.


  1. This article reminds me of the point the professor made about all the red apples being clones. Because we enjoy this one specific type of banana so much, it became the only one grown and consumed which indirectly caused the loss of genetic diversity. As we know, biodiversity has a large impact on everything including food production. Unfortunately, the fungus loves bananas as much as the next person and we can't stop them at the moment. Hopefully scientists can create a solution and bring our precious bananas back to pristine condition.

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  3. Most plants rely on fungi and hyphae to help get nutrients at the small cost of a bit of photosynthesis product. What's happening here is that the once favorable relationship is no longer mutually beneficial: so the relationship shifted to being parasitic again. The lack of variation is troubling and maybe if there were more variation, some strains would still prefer to associate with the fungus. The best hope for the banana is to shift back to making the fungus useful rather than moving away since it'll only fervently drive the parasitic fungus to remain associated with the banana roots.