You have probably never heard of the Asian citrus psyllid. But this insect, no bigger than the head of a pin, could be the reason that within a couple of years you will not be drinking orange juice or eating oranges from the U.S. The insect spreads a bacterium, which is harmless to humans and animals, but is devastating to citrus trees. Infected trees suffer from what has been called “citrus greening” because they produce green, misshapen fruit that is bitter and inedible. Once infected, the trees die within a few years. Since the insect clings to various parts of the tree, citrus greening can be spread by moving infected plant materials including bud wood, fruit and even leaves from one place to another. The disease has already killed millions of citrus plants in the southeastern United States and is threatening to spread across the country. There are no pesticides that are effective against the Asian citrus psyllid.
Since the infection is bacterial, one possibility is the use of antibiotics to try to curtail the problem. Interestingly, periwinkle plants are readily infected by the disease when exposed to lemon trees infected by citrus greening and respond well when treated with penicillin and some other antibacterial agents. Test are underway to see if these substances also work on infected citrus plants. The Madagascar periwinkle has already made a contribution to health in another arena. Vinblistine and vincristine isolated from the plant are used in chemotherapy.
Another approach involves genetic modification which could be helpful but comes with the baggage of public fear of the technology. Dr. Erik Mirkov, a Texas AgriLife Research plant pathologist, was actually interested in another disease known as citrus canker. He knew that some spinach proteins had antibacterial and anti-fungal properties and managed to insert the genes that code for these proteins into the DNA of citrus trees. The trees developed resistance to canker. As the problem of citrus greening became more and more important, he tested the spinach genes in citrus trees infected with the citrus psyllid. Early greenhouse tests looked good so field trials were begun and these also look hopeful.
But even if the technology pans out, the approval process is long and difficult. It’s expensive because it involves contracts with firms that do the actual testing with rats, bees, fish and maybe even songbirds It could take three to four years to complete, but it’s important of course to determine that the fruit produced from transgenic trees are safe to eat, especially by what are considered at-risk groups, which include infants, the elderly and those with compromised immune systems. The work is made easier by the fact that only proteins that are commonly eaten anyway are introduced into the crop. Saving citrus trees is not a minor issue and we need to explore all technologies that may play a role. Not only will the loss of the U.S. citrus industry have an effect on the availability and cost of citrus products, it will have a catastrophic fallout on the lives of citrus farmers and juice producers and thereby on the economy, especially of Florida.
