Aug 09 2010

The Bananas Hubbub

I love bananas. They are probably the most common fruit that I eat. Which is partly why I was intrigued when I learned that the cultivar of banana that I have known my entire life, the Cavendish, is an inferior variety to the banana that became popular in the first half of the 20th century, the Gros Michel.

This is a story of cultivation, economics, infection, and genetic engineering – with a promising update at the end. But let’s start with a little history.

The banana, despite the claims of “banana man” Ray Comfort, is a highly cultivated fruit. Evolved varieties are hard, contain large seeds, and are not very sweet. Cultivation resulted in the bananas we know and love – sweet, seedless, and creamy. Because they are seedless, they have to be propagated asexually through offshoots. This means that every Cavendish banana is a clone of every other one.

Photo by Timothy Pilgrim

There are many cultivars of bananas, and they fall into two basic types – dessert bananas that are sweet, and plantains that are more starchy and are generally not eaten raw. Most bananas are grown for local use in the tropics where they are native. They are used not only as a food staple but also the fibers are used for paper and other products.

Bananas generally do not make a good export fruit, because they bruise easily and ripen quickly – they don’t last long enough to ship to America and Europe. But in the late 19th century the Gros Michel variety was developed. This banana had a thick skin and ripened slowly, so that there was plenty of time to ship it abroad. The Gros Michel banana then became a popular import fruit in the US and Europe, and a large banana industry developed to meet growing demand.

However, the Gros Michel was susceptible to a fungal infection, Panama disease, that causes root rot. The industry ignored the threat until it was too late. Banana shortages began in the early 20th century (inspiring the song, Yes, We Have No Bananas), and in the 1950s the banana export industry started to collapse. By the 1960s Gros Michel banana plants were gone from plantations (they are not extinct – they still exist in small numbers).

The banana industry could not stop Panama disease, so they turned to another variety of banana, the Cavendish. There were initial fears that the Cavendish would not sell, as it was not as tasty, hardy, or creamy as the Gros Michel. But it was accepted, and now most people are not even aware of the fact that today’s bananas are a lesser cousin of the original export banana.

But all is not well in the banana industry. The Cavendish is still a cloned cultivar propagated through taking offshoots. This is an extreme example of a more general problem with agriculture – the lack of genetic diversity. Everyone picking the best crops to produce tends to limit diversity, which makes a crop more susceptible to infection and other problems. Genetic diversity is a hedge against extinction – a hedge our agriculture increasingly lacks. But bananas are and extreme example as there is practically no genetic diversity.

The Cavendish was initially resistant to Panama disease, but now half a century later Panama disease has evolved and adapted and is starting to infect the Cavendish cultivar. This is a problem without a current solution – researchers are essentially in a race against time. They either need to find a way to fight the Panama disease fungus (difficult and not likely), or they need to modify the Cavendish to be resistant to the current strains of Panama, or they need to cultivate yet another replacement for the export banana. (Perhaps each half century will have a different cultivar of banana they think of as “the” banana.)

Cavendish bananas for export are not the only bananas threatened by disease. All the seedless cultivars suffer the same problem of limited genetic diversity. There are several East African Highland cultivars of banana that are an important staple food crop for the region. They are being threatened by a different fungus, the Banana Xanthomonas Wilt (BXW). BXW threatens other crops as well. In addition, African bananas are threatened by banana bunchy top disease, a separate fungal infection. By reports 30 million Africans are dependent upon bananas as a food staple, and it is also an important cash crop for the region.

Attempts to control these infections with traditional means – by fighting the infections themselves – are failing. Attempts to use traditional breeding and cultivation techniques to develop a resistant cultivar have been sporadic and have failed to yield any results. The situation is actually quite dire.

But there is potential good news for East African banana farmers – researchers have managed to insert genes from the green pepper that convey resistance to BXW into a banana cultivar. Field testing still needs to be done, and if all goes well it will likely be years before local farmers benefit from the new GM varieties of banana, but this is good news for banana growers everywhere, and the millions who depend upon bananas for food.

Genetic engineering appears to be the only technology that will work quickly enough to develop resistant cultivars of banana before they are wiped out by infection. Dan Koeppel, author of Banana, believes it is our only hope of saving this important crop.

Conclusion

The story of the banana is a microcosm of the the strengths and weaknesses of modern agriculture, on which we increasingly depend to feed the billions of people who inhabit this world. Cultivars lack genetic diversity because of their asexual propagation. There is only one export dessert banana. The situation would be far better if bananas were like apples, with a multitude of local varieties, but this is not practical. Infections threaten large crop industries and traditional attempts to deal with this problem are failing, largely because they are too slow. Genetic engineering of resistant cultivars of banana, despite the troubled reputation of GM, might be our only hope of saving this important crop.

The banana is not just an optional desert fruit, as many westerners believe. While I would be sad to no longer have access to my favorite fruit, it would not threaten my diet. But for millions of people around the world the collapse of banana agriculture could mean starvation.

The phrase, “Yes, we have no bananas” could take on ironically sinister implications.

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