The bananas and the bees

Bananas went commercially extinct in 1965 and are likely to do so again. To make sense of this statement that is alarming fruit growers around the world, read on.

Children get some of their features from their father and some from their mother. This is because genetic material from both the parents is involved in creating the child. The same is true in plants, where pollen from one plant is used to fertilize the flower on another plant. The resulting seed has genetic material from both the parent plants and the tree arising from it inherits some properties from both the plants.

Now in the wild, the banana contains a mass of hard seeds making it inedible. But some 10,000 years ago, hunter gatherers in the Malaysian jungle stumbled across a plant that produced seedless, soft fruit. This was the result of a genetic mutation. The fruit was tasty, but the plant was sterile. It couldn’t produce any offspring.
wildbanana

Wild banana

That didn’t stop farmers, they learnt that they could re-plant cuttings of the tree and grow another sterile banana tree. But this method also meant that every banana tree grown this way was a genetic copy of the same tree.

Over the years (bananas were one of the earliest crops), there has been remarkably little genetic change in the various banana types all of which descend from a few forest mutants. This is not good for the health of the banana. It makes it less resistant to diseases.

Take this example, suppose a disease occurs which wipes out 90% of a population. The remaining 10% by some freak mutation prove more resistant to the disease. In the future if these 10% are allowed to breed, their offspring will also inherit their resistance. Before too long, the whole population may be resistant to the disease. This is the reason why penicillin is no longer as effective as it used to be. Many of the microbes it used to kill have developed into resistant populations.

The key to this system is that there should be a large number of genetically different individuals in the population so that whatever disease or disaster comes about, there may be some individuals who are resistant to it and can continue to breed.

On the other hand, if all bananas are genetic clones of each other, then a disease that can kill one banana tree can probably kill all banana trees.

This has happened before. Till the 1950s, the most commonly grown banana was a variety called the Gros Michel. It was a rich sweet fruit and didn’t have a bitter aftertaste when green. Unfortunately then a soil fungus called Panama disease wiped off the population of the Gros Michel till it became commercially insignificant.

 grismichelbanana

Gros Michel Banana

A new variety was found, the Chinese form known as the Cavendish which dominates world banana production now. Today, over half the bananas produced and exported are of this variety. Chances are that the bananas you got from the market are Cavendish.

cavendishbanana

Cavendish Banana

In 1990, in Malaysia a disease was found and named Tropical Race 4. This came from a soil fungus. A single clump of contaminated soil can spread the disease transported by wind, cars or water. The disease attacks the plant’s vascular system making it unable to draw water and nutrients from the soil.

India is the world’s leading producer of bananas and has hundreds of local varieties, but over the past 2 decades, the Cavendish variety has pushed out and replaced many of these. The mono-culture promoted by modern large scale farming only exacerbates the danger.

A similar story is seen in bees. The US honeybee population has seen a collapse in recent years. This is not just bad for bears and honey lovers, but also for farmers everywhere who depend on bees to pollinate their crops.

Honeybees originated in the old world and were brought to America by colonists. In 1622, Europeans introduced Apis mellifera mellifera, the “Dark Bee”. This was the only species till 1862 when Apis mellifera ligustica, the Italian or “golden honey bee” was introduced. Now the latter is most common.

 meliferamelifera

Apis mellifera mellifera

 

Apis mellifera ligustica

In 1922, a ban on bee imports to prevent the contagion of a tracheal mite meant a limited gene pool for the American bees. Today, the US beekeeping industry is suffering from the Varroa mite which feeds on bee blood and transmits diseases.

Genetic diversity has been found to be a key element in ensuring the survival of bee colonies. In a US Department of Agriculture study, it was found that colonies where the queen mated at least 7 were 2.86 times more likely to survive a 10 month working cycle than less diverse colonies.

But what about humans? Well, humans are believed to have originated in Africa and moved to the rest of the world. It is therefore not too surprising that there is far more genetic diversity in East Africa than in Europe or Asia.

 map-of-human-migrations

Map of Human migration inferred from Mitochondrial DNA

References

http://www.npr.org/sections/goatsandsoda/2017/02/14/511227050/why-killer-viruses-are-on-the-rise

http://entomology.ucdavis.edu/News/Increasing_Genetic_Diversity_of_Honey_Bees-A_Necessity_Says_Bee_Breeder-Geneticist_Susan_Cobey_in_Newly_Published_Book/

https://www.sciencedaily.com/releases/2013/06/130617111341.htm

http://www.conservationmagazine.org/2008/09/the-sterile-banana/

http://edition.cnn.com/2015/07/22/africa/banana-panama-disease/

https://www.ibe.upf-csic.es/home/-/asset_publisher/T2caeLMECPvW/content/id/5301613/maximized#.WLhW9m-GPmE

 

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3 responses to “The bananas and the bees

  1. Pingback: The bananas and the bees – Sayeh Erfan·

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