Storing bananas in the fridge WORKS!
I'm eating one that's been in there for nearly a week, the skin is thin and dark brown, but it's like a slightly green banana on the inside, just as it was when it went in. Amazing.
This has reminded me of a cautionary tale about banana preservation in another sense, told in several of my lectures over the years. I've looked up parts I don't remember in great detail, but most of this is the equivalent of biology student folk wisdom.
So. The humble banana is a striking example of the dangers of low genetic diversity. Genetic diversity describes how mixed the gene pool of a population is; how genetically similar the individuals are. The vast majority of plants are able to reproduce sexually, so new plants are made via some genetic mixing of their parents. This isn't about gene mutations per se, just new combinations of existing gene varieties. This keeps the population well mixed, and genetic diversity high (barring other factors I won't get into here). Wild bananas are no exception.
However, most cultivated bananas are. Here is a wild banana:
And here is one you might buy in a shop:
Wild bananas have large seeds. Due to a genetic quirk and encouraged by the fact that seeds aren't nice to eat, the seeds in the cultivated banana are so tiny I'm not even sure if they should be called seeds. They certainly won't grow into a plant1. New banana plants for plantations aren't grown from seed, but by cutting off part of a parent plant. The cut part can grow into an entire new plant quite happily - many plants can reproduce vegetatively like this. But most other plants use vegetative reproduction as a bonus and still make seeds. By not making seeds, cultivated bananas don't do any genetic mixing between generations. The daughter plants are clones of the parent. They miss out on the biggest force behind genetic diversity.
It is, in effect, a timebomb. Clones might be very well adapted to the current environment, but all of the population's eggs are in one basket, because if the environment changes all individuals have the same chance of suffering. There's no strange weirdo plant that struggled in normal conditions but happens to flourish in the new ones.
The problem for cultivated bananas came in the 1950s, when the nigh-indestructible fungus that causes Panama disease arrived in Central America. Most plantations used just one cultivar, 'Gros Michel' ('Fat Michael' - I wish I knew where that came from). Cultivars tend to have low genetic diversity as it is, but Gros Michel plants are virtually identical. Panama disease slaughtered them all with equal lack of mercy.
It must have been terrible to be a banana farmer. Your entire plantation could have been gone in a puff of spores. As far as I know, the epidemic didn't spread to the other banana centres of the world, but it was a very real possibility and Gros Michels as far away as East Asia were in peril.
Fortunately, it was discovered that a different cultivar did show resistance to Panama disease. This was Cavendish, which can be traced back to an Englishman who grew them in Derbyshire in the 1830s. So, growers across the world replaced their plantations of Gros Michel with those of Cavendish, and the crisis was over.
Do you notice a problem with this solution? Cavendish bananas are no more generically diverse than Gros Michel. That they happened to be resistant to Panama disease in the 50s does not make them intrinsically healthier plants. In fact, a new race of Panama disease is currently wreaking havoc among Cavendish bananas in Asia, Africa and Australia, enough that its Wikipedia page has a section titled 'Cavendish devastation era'. Solutions are being sought in hybrids with other bananas, searches for wild relatives, genetic engineering... all methods of changing the genetics of plants that have become hopeless at changing themselves. I really hope a sustainable fix is found soon.
*Despite their size, banana plants aren't trees, just very large plants. To be a tree, a plant needs to form wood, which requires secondary growth. This is basically when a stem can grow wider as well as longer.
This has reminded me of a cautionary tale about banana preservation in another sense, told in several of my lectures over the years. I've looked up parts I don't remember in great detail, but most of this is the equivalent of biology student folk wisdom.
So. The humble banana is a striking example of the dangers of low genetic diversity. Genetic diversity describes how mixed the gene pool of a population is; how genetically similar the individuals are. The vast majority of plants are able to reproduce sexually, so new plants are made via some genetic mixing of their parents. This isn't about gene mutations per se, just new combinations of existing gene varieties. This keeps the population well mixed, and genetic diversity high (barring other factors I won't get into here). Wild bananas are no exception.
However, most cultivated bananas are. Here is a wild banana:
 |
| Source: https://commons.wikimedia.org/wiki/File:Banana_with_Seeds.jpg |
 |
| Source: https://www.flickr.com/photos/carowallis1/1524840873 |
It is, in effect, a timebomb. Clones might be very well adapted to the current environment, but all of the population's eggs are in one basket, because if the environment changes all individuals have the same chance of suffering. There's no strange weirdo plant that struggled in normal conditions but happens to flourish in the new ones.
The problem for cultivated bananas came in the 1950s, when the nigh-indestructible fungus that causes Panama disease arrived in Central America. Most plantations used just one cultivar, 'Gros Michel' ('Fat Michael' - I wish I knew where that came from). Cultivars tend to have low genetic diversity as it is, but Gros Michel plants are virtually identical. Panama disease slaughtered them all with equal lack of mercy.
It must have been terrible to be a banana farmer. Your entire plantation could have been gone in a puff of spores. As far as I know, the epidemic didn't spread to the other banana centres of the world, but it was a very real possibility and Gros Michels as far away as East Asia were in peril.
Fortunately, it was discovered that a different cultivar did show resistance to Panama disease. This was Cavendish, which can be traced back to an Englishman who grew them in Derbyshire in the 1830s. So, growers across the world replaced their plantations of Gros Michel with those of Cavendish, and the crisis was over.
Do you notice a problem with this solution? Cavendish bananas are no more generically diverse than Gros Michel. That they happened to be resistant to Panama disease in the 50s does not make them intrinsically healthier plants. In fact, a new race of Panama disease is currently wreaking havoc among Cavendish bananas in Asia, Africa and Australia, enough that its Wikipedia page has a section titled 'Cavendish devastation era'. Solutions are being sought in hybrids with other bananas, searches for wild relatives, genetic engineering... all methods of changing the genetics of plants that have become hopeless at changing themselves. I really hope a sustainable fix is found soon.
*Despite their size, banana plants aren't trees, just very large plants. To be a tree, a plant needs to form wood, which requires secondary growth. This is basically when a stem can grow wider as well as longer.
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