No Sex Please, We’re Bananas

That’s a problem for our banana-munching republic. Sex was suspended for banana cultivation long ago, and the price we will pay is a Bananageddon. Here’s why.

The plant is propagated vegetatively and cannot produce seeds because it is genetically triploid. Two sets of chromosomes in a diploid plant are company, but three is a crowd because the threads of DNA get tangled and can’t segregate into equal halves to make haploid germ cells in male and female flowers. The vast banana plantations in the tropics are genetically identical clones, and the lack of diversity in these monocultures renders them vulnerable to pests that can evade their natural defenses.

There is only one kind of banana in the marketplace today, and its existence is threatened by the fungus Tropical Race Four whose hyphae kill after growing into the plant and cannot be eradicated from the soil. It has devastated crops in Asia and Australia because farming practices are so intensive, providing no physical or genetic barriers to the spread of disease. When it begins to rampage across the growing regions of Latin America bananas at 60 cents a pound will be a memory.

We have bananas
We have bananas

The fruit we love dangles on the thread of a single variety, whereas the many kinds of apples-Granny Smiths, Golden Delicious, McIntosh Red, etc- are begotten from sexual unions and seed dispersal. Until sixty years ago the Gros Michel was the big banana, with a less attractive name than the Cavendish which is currently the reigning monarch of the bunch. I am told that the Gros was the more tasty of the two, although I can’t remember because I was too young, being born around the year 10 BCE (Before Cavendish Era). When Gros plantations came under attack by an earlier disease, the Cavendish was planted as a substitute because of its greater resistance, but now it too is under a threat.

The Cavendish is an aristocratic banana. Sometime in the 1830s it was grown on the estate of the Duke of Devonshire of the Cavendish family, whose stately home is the famous Chatsworth House in Derbyshire.  The 6th Duke recognized an outstanding talent in his boy gardener, Joseph Paxton, who designed the greatest greenhouse in the world for his master, and which became the inspiration for his plan of the Crystal Palace at the Great Exhibition of 1851. Sir Joseph, as he later became, was one of the most ingenious men of the Victorian Age, and all because of the Duke’s trust and confidence.

One of his claims to fame was to grow in his greenhouse the variety of banana that now adorns our fruit bowl; as a young man, Joseph never asked what bananas could do for him, but asked what he could do for bananas. The Cavendish is his gift to the world, and it is a shame that the Devonshire family motto can’t be changed from Cavendo tutus to Deus nisi quod fixa (meaning God save the banana). But I digress…

In the past few weeks, banana biologists have announced the genome sequence of their fruit. The Bananome will enable them to peel open the fruit for genetic engineering to confer resistance to specific diseases and boost its nutritional bounty, perhaps by augmenting vitamin A whose deficiency still causes blindness in children. We will then have to choose GMO bananas or have no bananas, but genetic engineering will be fruitless unless vegetative propagation is bypassed for making new cultivars. To straighten our banana troubles we need to suspend cloning in this Brave New World long enough for a bunch of native plants to have wild sex.

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