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Bananas Are Dying. Again.

April 27, 2022

You’ve probably eaten a banana before. You’ve probably even eaten one this week in a smoothie, in a baked good, or just by itself for a quick snack or breakfast. Bananas are a titan amongst the agricultural industry with a retail value between $20-25 billion dollars, making them a vital part of the economies of many Latin American countries like Panama and Ecuador.

What you probably don’t know is that pretty much every single banana you’ve ever eaten is from the same variant, the Cavendish. These delicious plants replaced the Gros Michel, or Big Mike, banana as the star of the banana industry back in the 1960s when the Big Mike went nearly extinct. However, history is repeating itself and now the Cavendish banana is on the chopping block all due to the same reason: Fusarium wilt, or Panama disease.

An Old Foe Returns for Revenge

Fusarium wilt is a fungi that completely ravishes the soil and plants it touches. When affecting a plant, the fungi goes around 10 feet deep into the soil making it so that just removing a single affected plant to stop the spread is nearly impossible. Large areas of soil become barren, and the fungi can be easily tracked to other places on the bottom of other workers’ shoes or car tires. Tropical Race 1 of this disease began killing Gros Michel in large quantities in the early 20th century, so the resistant Cavendish took its place in the industry; however, now the Tropical Race 4 variant (TR4) has crumbled the Cavendish’s resistance.

The deadliness of TR4 has only been heightened by the monoculture system of the banana industry. Since nearly every banana sold commercially is the Cavendish, a variant without seeds for easier consumption, Cavendish bananas must be propagated from existing growths causing them to be near genetic copies of one another. This small gene pool decreases the Cavendish’s resistance to diseases like TR4 and once one banana plant is affected, it can easily spread to other batches and destroy new ones.

Stop the Spread!

Can the Cavendish banana be saved or will it fall to the same fate as its predecessor, Big Mike? There have been a couple of attempts to solve the issue at hand with varying degrees of success:

  • Genetically Modified Cavendish: In 2019, Dr. James Dale successfully modified a batch of Cavendish bananas with a gene from a TR4-resistant banana. However, the fear and bans of GMOs in many countries has kept this from becoming an appealing solution.
  • Breeding Cavendish with resistant bananas: KeyGene has been attempting to traditionally breed a Cavendish with a resistant banana to try to get around the GMO dilemma. However, these resistant bananas tend to be inedible ones full of seeds, and through traditional breeding, it is difficult to get the exact results desired to produce a delicious yet TR4 disease-resistant banana.
  • Diversify the banana industry: Breaking free of monoculture to grow and sell multiple kinds of bananas would make it much more difficult for an entire breed to be fully wiped out like Big Mike was. However, the banana industry is completely modeled around monoculture and to change this would need a large sum of money and structural alterations that companies are not willing to make at this moment.
  • Biosecurity protocol: This is the one solution currently being used by most banana farms. Areas where an affected plant has been identified will be zoned off and destroyed. Workers must also walk along cement paths and utilize foot and car tire washing areas to try to diminish possible contaminated soil tracking to other locations. These measures have been working so far as to slow the spread of TR4.

 

There is still a lot of uncertainty with the Cavendish banana’s future, and one day, you might not be able to taste it again. Cherish each banana you eat because just like you, they’re surviving through a pandemic right now too!

 

Citations

Abby Narishkin, S. C. (2021, July 29). Why the world’s favorite banana may go extinct, and how scientists are trying to save it. Business Insider. https://www.businessinsider.com/cavendish-banana-may-go-extinct-disease-2021-6#:~:text=Similar%20to%20humans%2C%20bananas%20are,the%20%2425%20billion%20banana%20industry.

Kambhampaty, A. P. (2019, November 18). What we can learn from the near-extinction of bananas. Time. https://time.com/5730790/banana-panama-disease/

 

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About Author

Lindsay is a undergraduate Computational Media student at Georgia Tech. She loves reviewing the history of medicine and science and making connections to the present-day. In her free time, she loves drawing cartoons and painting.

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.