A pandemic is destroying orange groves in Florida. The disease, called citrus greening, is also spreading to citrus groves in Texas and California, threatening a more than $3 billion per year industry.

If left unaddressed, the entire U.S. citrus industry could be wiped out and, as Florida Sen. Bill Nelson said, "We’ll end up paying $5 for an orange – and it’ll have to be one imported from someplace else.”

Citrus greening disease is spread by bacteria that block trees' nutrient and water channels and prevent fruit from ripening.

"It’s like choking the tree from the inside out,” said David Gang, a Washington State University molecular biologist and biochemist who is collaborating with a large, interdisciplinary team to combat the disease.

Insect spreads disease

The bacteria are hosted and spread by an insect related to aphids and whiteflies called the Asian citrus psyllid (pronounced sill-id). The disease is thought to have spread from China in the early 2000s. Citrus greening has already destroyed the citrus industry in Jamaica.

The invasive psyllids pierce the citrus trees with a needle-like mouthpiece, similar to the way a malaria-transmitting mosquito infects its victims. As it feeds on the tree’s water and nutrients, the psyllid injects the disease-causing bacteria, which then spread through the rest of the plant. 

To combat this aggressive disease, the U.S. Department of Agriculture has funded a multifaceted, multi-institutional initiative involving more than 40 researchers located in several states. Scientists are looking at the disease's ecological consequences, the biology of citrus trees, the insects and the mechanism by which the insect transmits the bacteria.

 

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Pesticides have been of some use in controlling the psyllids but researchers are concerned the insects will develop resistance. And biocontrols – siccing good bugs to prey on the bad ones – have proven ineffective because the psyllids simply outbreed their predators.

That’s where David Gang enters the scene.

Altering the insect

Gang’s lab in the WSU Institute of Biological Chemistry focuses on using new technologies like genomics and proteomics to study plant defense mechanisms, particularly the chemical compounds that help plants survive and combat pathogens and pests. In the USDA-funded project, Gang and his colleagues isolate and sequence the genes being expressed in the psyllids as they feed on citrus plants.