Citrus greening, the plague that could wipe out Florida's $9 billion orange industry, begins with the touch of a jumpy brown bug on a sun-kissed leaf.

From there, the bacterial disease incubates in the tree's roots, then moves back up the trunk in full force, causing nutrient flows to seize up. Leaves turn yellow, and the oranges, deprived of sugars from the leaves, remain green, sour, and hard. Many fall before harvest, brown necrotic flesh ringing failed stems.

For the past decade, Florida's oranges have been literally starving.

Since it first appeared in 2005, citrus greening, also known by its Chinese name, huanglongbing, has swept across Florida's groves like a flood. With no hills to block it, the Asian citrus psyllidthe invasive aphid relative that carries the diseasehas infected nearly every orchard in the state.

By one estimate, 80 percent of Florida's citrus trees are infected and declining.

The disease has spread beyond Florida to nearly every orange-growing region in the United States. Despite many generations of breeding by humanity, no citrus plant resists greening; it afflicts lemons, grapefruits, and other citrus species as well. Once a tree is infected, it will die. (See "Can Parasitic Wasps Help Save America's Citrus?")

Yet in a few select Floridian orchards, there are now trees that, thanks to innovative technology, can fight the greening tide. These trees have the potential to keep Florida orange juice on your breakfast tableprovided you are willing to drink the juice of oranges that have been genetically modified to contain genes from spinach. (Read "The Next Green Revolution" in National Geographic magazine.)

The trees are the work of Erik Mirkov, a plant pathologist at Texas A&M University who has spent his career applying the tools of biotechnology to citrus. Over the past few years, his research on genetically modified oranges has gone from an academic sideshow to one of the great hopes of the industry.

It's highly unlikely, researchers and growers agree, that oranges will remain in Florida unless new, modified strains like Mirkov's are widely growna view endorsed by the National Research Council several years ago.

Citrus greening incubates in the tree's roots, making it difficult to detect infection. A healthy citrus root system is shown at left, and an infected one at right.

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Can Genetic Engineering Save the Florida Orange?

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