Geneticists enlist engineered virus and CRISPR to battle citrus disease

Desperate farmers hope scientists can beat pathogen that is wrecking the US orange harvest. 

Fruit farmers in the United States have long feared the arrival of harmful citrus tristeza virus to their fields. But now, this devastating pathogen could be their best hope as they battle a much worse disease that is laying waste to citrus crops across the south of the country.

The agricultural company Southern Gardens Citrus in Clewiston, Florida, applied to the US Department of Agriculture (USDA) in February for permission to use an engineered version of the citrus tristeza virus (CTV) to attack the bacterium behind citrus greening. This disease has slashed US orange production in half over the past decade, and threatens to destroy the US$ 3.3-billion industry entirely.

The required public comment period on the application ended last week, and the USDA will now assess the possible environmental effects of the engineered virus.

Field trials of engineered CTV are already under way. If the request is approved, it would be the first time this approach has been used commercially. It could also provide an opportunity to sidestep the regulations and public stigma attached to genetically engineered crops.

The engineered virus is just one option being explored to tackle citrus greening. Other projects aim to edit the genome of citrus trees using CRISPR–Cas9 to make them more resistant to the pest, or engineer trees to express defence genes or short RNA molecules that prevent disease transmission. Local growers have also helped to fund an international project that has sequenced citrus trees to hunt for more weapons against citrus greening.