Monday, December 21, 2015

Genetically engineering: Bananas and bad situations

Sometimes you can breed yourself out of a bad agricultural situation.

Sometimes you can genetically engineer yourself out of it.

And sometimes you just give up.

(Image: Banana suffering from Fusarium wilt. Credit: American Phytopathological Society.)

Traditional plant breeders look for traits in closely related varieties that they can cross-breed into commercial varieties of crops.

Grape breeders, as an example, are working hard to breed fungus resistant varieties with commercially appealing varieties to develop commercial crops that don’t need so much fungicide. 

But breeding doesn’t always work and it can be very slow. The story of pineapple in Hawai`i is an example. 

The Pineapple Research Institute developed tens of thousands of crosses with various qualities, but found little that could beat the industry standard, the Smooth Cayenne. Some of their varieties have made it into the fresh pineapple industry, but they’re not perfect.

Genetic engineering provides a leg up on standard breeding. The most famous Hawaiian example is the insertion of a part of the ringspot papaya virus into papayas, to cause the papaya to be resistant to that virus—a kind of genetic inoculation against disease.

There has been a lot of criticism of combining distant species genetically, but in some cases traditional breeding even between close species doesn’t work well—like potatoes. There, a technique called cisgenesis has been used to cross potato relatives to get disease resistance from one potato into another potato, when traditional breeding doesn’t work. 

They’re still potato genes added to potato genes, but genetic engineering techniques are used because it’s hard to get them to cross naturally.

With bananas, when a fungal disease attacked the world’s most popular banana variety, Gros Michel, the world took Door Number Three: it gave up on the Gros Michel. There was no cure, and the banana was very susceptible, and the technology wasn't very advanced.

The Fusarium wilt essentially killed off the banana that had dominated the industry for a century—the tasty banana that made bananas popular.

If you’re old enough to remember the Gros Michel, you know how good a banana can be. Growers switched to the blander Cavendish. Not as tasty, but it was resistant to the fungus that killed the Gros Michel.

Now, a new crisis has arisen. There’s a new disease attacking the Cavendish. It is a soil fungus related to the one that killed Gros Michel. It is called Fusarium oxysporum f. sp.cubense (Foc), and is commonly called Fusarium wilt or Panama disease.

A good review of the issue is at the ProMusa site. (Musa is the name of the banana genus.) 

There is some suggestion that there might be Fusarium-resistant strains of Cavendish. Growers from the Philippines are shipping partially resistant Cavendish bananas, but most folks don't consider that a final solution.

Most industry folks suggest that the only savior is likely to be genetic engineering. Even the leftist literary leader Mother Jones says so. “The only way to save your beloved bananas might be genetic engineering,” says the headline in today’s issue (December 21, 2015)

If you simply switched to a different banana variety, the Fusarium fungus might just target that one next, Mother Jones author Maddie Oatman worries.

Why does any of this matter? Because banana is the most popular fruit in the world. As a report in the PLOS Pathogens journal says, they are grown in tropical and subtropical areas globally. For many cultures globally, banana eating and banana growing are essential to survival.

As happened with the Gros Michel, most of the Cavendish bananas are clones of each other—meaning a disease that gets traction can get lot of traction.

“Any disease management eventually fails in a highly susceptible monoculture,” that article says.

There’s a lot going on with bananas. Research labs around the world are working on genetic solutions. Classic breeding is problematic in bananas, and most domesticated bananas have been selected from among wild varieties, not bred.

One question is that if we’re going to make a banana resistant to Fusarium wilt anyway, then instead of the Cavendish, seems like it would make sense to go after the Gros Michel—a much tastier banana? 

And if we can get any good Fusarium resistant banana, how soon will it be available. I’ll be trying to get an answer to those questions.

© Jan TenBruggencate 2015

1 comment:

Kolea Lover said...

Thank you for all of your postings, and for the clarification about the kolea season --- from your confused kolea lover!