Can a genetic tune-up save the orange?

Oz citrus

When the Asian citrus psyllid first introduced its noxious stowaway – the Liberibacter bacterium that infects citrus plants and ruins their fruit – to Florida’s orange groves in 2005, the state’s growers, who had been monitoring the insect since first observing it in 1998, had been preparing for seven years. But they weren’t even close to being ready.

Florida’s citrus acreage has shrunk by about a third over the last decade, and Huanglongbing (HLB), or citrus greening disease, has been a major contributor to this decline. In December 2013, USDA’s crop forecast for the season was revised downward, again, to 121 million boxes, more than 10 percent less than the previous year. The cause of the decrease was soured, shrunken, or fallen fruit, caused by HLB. For the earlier-ripening non-Valencia oranges, the report states, “Current droppage, above the maximum and steadily increasing, is projected to be highest in the series dating back to 1960-1961.” The report was so alarming that USDA promptly formed an emergency response framework, consisting of federal, state, and industry partners, to coordinate and combine research efforts.

huanglongbing Psyllid

The Asian citrus psyllid is an efficient vector of the bacterial citrus disease huanglongbing (HLB). Center for Invasive Species Research photo

American agriculture seems to have grown calluses against seemingly near-constant reports of catastrophe, and it’s possible that many Americans could misunderstand the threat posed by HLB. To be clear: The nation’s commercial orange groves are fighting for their lives. Growers have tried everything: pesticides, nutrient supplements, biocontrols, and quarantines; they’ve searched the world for HLB-resistant citrus. All these approaches have failed. The rate of HLB infection is not slowing among Florida oranges: It’s increasing.

Faced with an existential threat to his company’s 21,500 acres of orange trees, Ricke Kress, president of Southern Gardens Citrus in Clewiston, Fla., launched a search for a transgenic orange plant that could stand up to Liberibacter. “I have yet to meet a researcher in the world that doesn’t feel that the ultimate solution to this disease will be genetic,” he said. “Every one of us wishes we could find something easier, but nobody has. And so we’re working with the idea that the long-term solution could be a genetic modification.”

After considering several alternatives, Southern Gardens Citrus is focused on a modification pioneered by Erik Mirkov of Texas A&M University, which uses a gene extracted from spinach DNA to activate a defense against HLB infection. The company has planted several experimental plots of these trees, which remain under federal supervision; the first were put in the ground in 2009. “We’ve modified those initial trees to be more resistant,” Kress said, “and we’ve got more trees in the ground. We have different generations coming along, and we’re seeing some pretty positive results right now. But the proof is in the ground.” Growing mature, commercially productive trees – and earning regulatory approval for their fruit – will take a few more years.

Southern Gardens Citrus planted research field trials of potential canker and greening disease-resistant citrus trees in its Hendry County citrus groves. The trees, noted to be resistant to canker and greening in the lab, were planted in small plots to determine if the trees are disease resistant under commercial grove conditions. Photo courtesy Southern Gardens Citrus

Southern Gardens Citrus planted research field trials of potential canker and greening disease-resistant citrus trees in its Hendry County citrus groves. The trees, noted to be resistant to canker and greening in the lab, were planted in small plots to determine if the trees are disease resistant under commercial grove conditions. Photo courtesy Southern Gardens Citrus

Even assuming everything goes as he hopes, Kress concedes he isn’t sure the orange industry will ever be what it was. Though the seriousness of the HLB pandemic is enough to convince many – even the staunchest skeptics of genetically modified crops (www.motherjones.com/tom-philpott/2013/08/what-does-looming-citrus-apocalypse-tell-us-about-gmos) – that biotechnology may be the commercial orange’s only hope, it may take an additional few years before American consumers decide they’re ready to drink the juice of transgenic oranges. For growers such as Kress, that’s something to worry about later. Without saving the orange from HLB, it won’t be anything to worry about at all.

Leave a Comment

  • (will not be published)