Nematodes Photo Credit: Matthieu Godbout [CC-by-SA 3.0], via Wikimedia Commons.

Genetically modified foods have caused a lot of controversy among environmentalists. Some worry that these so-called “Frankenfoods” might disrupt the ecosystems they grow in, or even threaten human health. But others praise their potential to offset other environmental problems. For example, in this Science Update, you’ll hear how genetically engineered tomatoes may be able to resist parasitic worms without the use of toxic pesticides.


Outsmarting a tricky worm. I'm Bob Hirshon and this is Science Update.

For a worm, the nematode’s pretty clever. The tiny parasite attacks a single cell on a plant’s root, and turns the cell into its own endless buffet table. The worm does this by taking over the cell’s machinery, forcing the cell to ask for more and more food from the rest of the plant. Soon, the whole plant’s working just to support that one cell-- and the hungry worm inside. The result is billions of dollars in damage to crops each year, and tons of noxious pesticides being dumped onto crop lands.

At The University of California at Davis, Valerie Williamson’s studying nematodes, and coming up with new ways to stop them. She says that some wild tomato plants have developed a clever way to fight back: as soon as a cell is attacked, it commits suicide.


And therefore the nematode can’t feed, and it can’t develop, it can’t get nutrients from the plant, and the plant is perfectly happy without these cells, it can replace them with other cells where the nematodes are not present, and it will do just fine.

Williamson’s goal is to take the gene that performs this trick and transfer it into other crops. The hope is that worm-resistant plants will mean far greater yields, with fewer pesticides. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

First of all, it’s worth stating that the tiny worms in this story are ravenous plant-killers. They attack over a thousand different species of plants around the world, from Africa to the United States, including a wide variety of important crops. The estimated damage from these worms adds up to $100 billion worldwide. So this small worm is no small problem.

As Williamson explains, if the worms can successfully infiltrate just one cell on the plant’s root, eventually they’ll have the whole plant working for them. The nematode siphons off all of the plant’s nutrients, which normally would go toward the production of fruit, leaves, and other parts that are valued by the plant and by human farmers. It’s not known exactly how the nematodes find their way to the root cells and set this sabotage in motion. But the consequences are clear: the plant loses the ability to make the parts it needs to make, and also becomes vulnerable to root damage and fungal infections at the site where they’re being chomped.

The story of the plants that fight back begins in the 1940’s, when UC Davis researchers found a wild tomato plant that just happened to be resistant to these nematodes, and cross-bred it with a cultivated tomato plant that produces edible, grocery-quality fruit. The result was a line of naturally resistant tomato plants that’s been grown in California for over fifty years, with fewer pesticides than most tomato farms require.

What’s new here is that the researchers have isolated a single gene that causes this resistance, and are transferring it into other tomato plants. The advantage of this is precision: with genetic engineering, you transfer only the gene you’re interested in. With traditional cross-breeding, you mix in a lot of other genes you might not want. For example, the fruit of the original wild tomato plant is tiny, green, and tastes terrible. It takes a lot of time and effort to breed undesirable traits like this back out of a plant, after you’ve bred in the traits you want. Inserting a single desirable gene gets around this problem.

The other advantage to this technique is that you can transfer the tomato gene into other crops, like yams, without ending up with a weird “yamato” (or, more likely, nothing). In fact, Williamson and her colleagues are already working on this project with scientists and farmers in Nigeria, where the yam is one of the most important food crops.

Now try and answer these questions:

  1. Why are these nematodes such a problem? How do they attack plants?
  2. How do the resistant plants stop the nematodes from doing any major damage?
  3. What are the advantages of genetic engineering over traditional cross-breeding?
  4. Can you think of other traits that farmers might want to genetically engineer into tomato plants? What about other crops?
  5. Some people worry that genetically engineered plants might have an unforeseen negative impact on the environment. How do you think this might happen? In the case of the genetically engineered tomatoes, how might scientists watch out for these sorts of problems?

For Educators

To learn more about all kinds of parasites, including worms, bugs, and bacteria, check out National Geographic’s Parasite page.

This article, Modified Crops Could Lead to "Superweeds," Study Suggests, describes one potential hazard of genetic engineering in plants: the possibility that weeds may pick up designer genes that were meant to make crops tougher, resulting in “superweeds.”

You might want to look at these lesson plans on genetic engineering in agriculture, and its risks and rewards, by the New York Times Learning Network:

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