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Cold, Hard Facts About Saving Florida's Oranges

Exceptionally cold temperatures and a vicious bacterium are giving the Sunshine State's citrus trees a battle, but science in on the oranges' side.

Orange juice concentrate — the frozen food staple routinely gobbed out in breakfast pitchers — now makes up the bulk of Florida's citrus industry. It's even traded as a commodity on the New York Board of Trade.

But before it becomes a twinkle in the eye of an ambitious futures trader, the oranges themselves must first hazard the Sunshine State's sometimes unpredictable winters. And, of late, they haven't been all balmy and mild.

A late December and early January cold snap saw temperatures in south and central Florida drop from shirt-sleeve weather to sub-freezing. Those crucial sub-freezing hours can make the difference between an orange grove free from the scourges of winter frost and higher prices in the check-out line.

For well over a century, however, the U.S. Department of Agriculture citrus-breeding program has been trying to make citrus trees more resistant to winter freezes.

While all commercial citrus is evergreen, the key to solving the problem of cold hardiness lies in Poncirus trifoliata, aka the "trifoliate orange," a deciduous species that is the most cold hardy of any citrus out there. It originated in northern China, and in the U.S. can now be found as far north as Pennsylvania.

Problem is, it produces a small, seedy and completely unpalatable piece of fruit.

"Even its direct hybrids taste terrible," said horticulturalist Ed Stover at the USDA's agricultural research station at Florida's Fort Pierce. "But the idea is to combine some of Poncirus' cold tolerance with the fruit quality of cultivated citrus. This is hybridization, not genetic engineering. We plan on testing cold hardiness in some fourth-, fifth- and sixth-generation hybrids."

This spring, Stover and colleagues will plant some hundred of these orange hybrids at a couple of sites in north Florida, perhaps as far north as Live Oak and Ocala. Over the next 10 years, the aim is to identify citrus varieties capable of tolerating once-in-a-decade type freezing within the northern fringe of Florida's citrus belt.

As for damage to this year's citrus crop, citrus extension agent Chris Oswalt of Florida's orange-rich, south-central Polk County, said that while leaf loss and fruit damage are a given, he doesn't expect his county to lose actual trees.

That's not a bad outcome for fruit that actually originated in tropical Asia.

Citrus has been culturally synonymous with Florida for centuries — orange trees were first grown in the late 16th century around St. Augustine on the then Spanish colony's northeast coast. By the 18th century, English colonists were planting citrus as far north as South Carolina — until an 1835 freeze spurred citrus' gradual retreat back to Florida. Today, some 850,000 acres of commercial Florida citrus lie mostly south of Orlando.

Despite this winter's early low temperatures, however, the question on most citrus growers' minds is not how to weather this latest bout of inscrutable winter, but how to counter the more immediate danger of Greening Huanglongbing disease,

Greening disease causes fruit and leaf discoloration as a result of the ravages of its signature bacterium, Candidatus Liberibacter asiaticus.

The bacterium is spread by a small flying insect about the size of a fruit fly — the Asian citrus psyllid, which was initially identified in Florida more than a decade ago. Greening disease itself was first found in Florida in late 2005.

Greening has already also been found in Georgia, Louisiana and South Carolina, and the USDA is worried the disease might spread to Texas, Arizona and California.

"We're now losing citrus to real estate development and disease," said horticulturalist Gene Albrigo at the University of Florida's citrus research and education center in Lake Alfred. "Some individual groves in the south have probably lost 20 or 30 percent due to Greening."

But could Florida's recent cold have also provided a silver lining by serendipitously reducing Greening disease's pesky psyllid population, the same way it's taken a shot at invasive iguanas and pythons?

"You would hope that the cold would reduce some of the psyllids," Oswalt said. "But it won't completely get rid of them."

So, for now, making the citrus trees resistant to the Asiaticus bacterium remains the most practical option. One scenario involves genetically inserting anti-microbial amino acid compounds from plants like soy beans or spinach. Researchers are hopeful that Greening can be dealt with swiftly in the not too distant future.

Citrus' continual struggles with old man winter, however, will likely continue for decades.

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