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Botanically speaking the banana is the largest herb (the ‘tree’ is actually a ‘pseudostem’) and the part we eat is technically a berry. Weird right? It gets weirder, they’re also clones.
Since they were first domesticated by humans 10,000 years ago, bananas have been grown and enjoyed in many places around the world. Prior to domestication, wild bananas were filled with large seeds, which as you can imagine, made them undesirable to eat. After years of cross breeding wild varieties, and selecting for varieties that had fewer seeds, new seedless bananas were created. The most popular variety available today is called the Cavendish banana.
While crossbreeding has created the Cavendish banana with its delicious seedless fruit, it also resulted in those bananas becoming sterile and they are unable to reproduce sexually. Humans typically have two copies of each of their chromosomes, one from mom and one from dad. Domesticated bananas, however, have three copies of each of their chromosomes, one copy from one parent and two copies from the other parent. The banana’s three chromosomes can’t be equally divided to create sex cells (sperm in the pollen, and the egg in the ovary) which means they are sterile and unable to produce sexually to produce viable seeds. So, if domesticated bananas can’t produce seeds where do all the banana plants come from? Cloning!
The banana plant grows in an interesting way, it produces ‘suckers’ which are genetically identical to the original plant. These suckers can be cut off the original plant, planted in the ground, and they will grow into a fruit producing plant too. (This process is called propagation, and you can do it at home with many of your houseplants.) This makes for an easy way to create great numbers of banana plants that produce yummy fruit, but there is a downside too. All the plants grown this way are genetically identical, which makes them very susceptible to disease.
Before the Cavendish variety became so popular, the most desirable banana variety was one called ‘Gros Michel’. These fell out of favor because they were susceptible to a fungal disease called Panama disease. Thankfully, the Cavendish was resistant to the disease, which is why they became the most popular variety, accounting for 99% of banana exports to developed countries. However, Cavendish bananas are now facing their own threat from fungal diseases. Because the plantations have no genetic diversity these diseases can spread quickly through plantations and destroy the plants. If nothing is done, the Cavendish bananas will likely go the way of the Gros Michel and be relegated to memory.
Thankfully, genomics is allowing researchers to identify disease resistant genes in both domesticated and wild banana varieties. This will help banana growers identify new varieties that are not only resistant to disease but are also yummy.
To read more about this research you may like to read this story from the Smithsonian magazine.
You may also like to read our Quick Snip about researchers looking for ways to save the Cavendish.