Citrus greening (also called Huanglongbing or HLB) is an infectious disease affecting citrus trees in Florida. It is a bacterium, Candidatus Liberibacter asiaticus, and spread by an invasive fly, the Asian citrus psyllid. Since 2004 it has caused a reduction in the Florida citrus industry by 90% and doubled production costs. It is close to completely wiping out the Florida citrus industry. Various methods have been tried to keep it under control, but they have all failed.

There is good news, however. The University of Florida in collaboration with the company Soilcea, has developed a GMO orange that is highly resistant to citrus greening. They expect to have commercial trees available by the Spring of 2027. The limiting factor is that it takes years to grow test trees to see that they remain resistant and produce viable fruit. So far the test trees are doing well.

The company licensed the finding of Nian Wang, a professor at the University of Florida, who found that the bacterium is dependent upon interactions with the host that can be traced to several genes. The company used CRISPR to silence those genes, making it more difficult for the bacterium to infect plants and thereby making the plants resistant to infection. This approach has apparently worked, although again we won’t be sure until the first test trees reach maturity.

Also, the USDA has determined that these genetically altered cultivars do not qualify as subject to regulation under Federal rules, which removes a significant barrier to commercialization. This is a bit of a controversy. The USDA in 2020 decided to exempt certain kinds of genetic engineering from requiring USDA approval. For example, if you are simply silencing existing genes that was no longer considered a “GMO”, because no new genes were being introduced. However a court later struck down that ruling saying that the USDA still has to review and approve those cultivars. This makes the current USDA decision interesting – they are essentially saying that this cultivar does not fall within their regulatory sphere.

“APHIS did not identify any plausible pathway by which your modified sweet orange, or any sexually compatible relatives, would pose an increased plant pest risk relative to comparator sweet orange plants,” the agency said in the regulatory determination.

The EPA also has to determine there is no environmental risk. The FDA has to determine that the resulting oranges are substantially similar to existing varieties and therefore pose no health risk. Give the nature of these modifications, these should not be significant barriers.

At this point it is very possible that these CRISPR modified oranges that are substantially resistant to HLB will save and revitalize the Florida citrus industry. This is exactly what has already happened in the Hawaiian papaya industry. The industry was almost wiped out by the ring spot virus. A GMO papaya was introduced which saved the industry. Like these oranges, the GMO papayas were created through silencing an existing gene rather than introducing a new gene. Hawaii culturally remains anti-GMO, but the state quietly carved out an exception for the GMO papaya.

We are also seeing the same thing with the American chestnut. This tree was mostly wiped out by an Asian fungus. A GMO variety resistant to the fungus has been created, although there is a question about how well they are performing in the field. Researchers may need to do some more genetic tweaking before they get a variety that is worth planting widespread.

Last year a GMO variety of banana resistant to the Tropical Race-4 fungus which is currently wiping out the commercial Cavendish banana industry, was approved for human consumption in Australia and New Zealand. This genetic variety makes the banana plants almost immune to the fungus. While it is currently considered a backup plan if other attempts at fighting the fungus fail, this variety will very likely be necessary to save the banana industry.

It is now a simple fact of life that in order to grow enough food to feed the world, we need massive agriculture. Growing a lot of the same plants invites pests, and so like it or not we are now in an arms race with pests. There are lots of things we can do to mitigate pests, and most experts recommend integrated pest management which uses a variety of methods together. But even still, in many cases we are simply losing this battle.

The only technology that is fast and powerful enough to keep up with evolving pests, and the spread of pests caused by globalization, is genetic engineering. We are fortunate that genetic technology has advanced so much so quickly over the last 20 years. Without it agricultural industries would be toppling one-by-one in the face of evolving pests. So far the anti-GMO propaganda industry has either opposed these crop-saving cultivars, usually by saying they are not necessary, or they quietly ignore them and focus their attention elsewhere. What they never do is admit that GMO technology has saved entire crop industries and will be necessary to save more in the future.