Spinach could be weapon against citrus scourge

By Christopher Sherman

Associated Press

Published: Friday, March 30 2012 5:15 p.m. MDT

A "Hamlin" sweet orange tree carrying spinach genes grafted on a non-transgenic rootstock called Rough Lemon grows Wednesday, March 28, 2012, in a lab at the Texas AgriLife Research and Extension Center in Weslaco, Texas. Testing has shown the genetically enhanced citrus trees are immune to citrus greening, a disease that has ravaged the industry.

Christopher Sherman, Associated Press

WESLACO, Texas — In a lab not far from the Mexican border, the fight against a disease ravaging the worldwide citrus industry has found an unexpected weapon: spinach.

A scientist at Texas A&M's Texas AgriLife Research and Extension Center is moving a pair of bacteria-fighting proteins naturally occurring in spinach into citrus trees to fight a scourge commonly known as citrus greening. The disease hasn't faced this defense before and intensive greenhouse testing so far indicates the genetically enhanced trees are immune to its advances.

Next month, dozens of young sweet orange and grapefruit trees developed by Texas plant pathologist Erik Mirkov will be planted near Lake Okeechobee in South Florida to see how they fare in a commercial citrus grove.

"Some of these growers in Florida, they say 'If you can't have something for us in five years, if you tell me it's going to take eight we're dead,'" Mirkov said.

To hurry along the process, Mirkov and Southern Gardens Citrus, a subsidiary of U.S. Sugar that is funding his research, are pursuing government regulatory approvals while their field testing continues.

The effort was given extra urgency Friday, when the California Department of Food and Agriculture announced that citrus greening had for the first time been found in the state. A tree was found to be infected in a lemon/pummelo tree in a residential neighborhood of Los Angeles County.

Citrus greening was first described in China in the early 1900s as Huanglongbing, which growers and researchers refer to as HLB. The bacterium is carried from an infected tree to healthy ones by the Asian citrus psyllid, a tiny dappled brown insect that showed up in Florida in 1998. The bacterium reproduces and spreads through an infected tree's vascular system making it difficult to take up water and nutrients.

Trees produce smaller fruit that drops to the ground prematurely, and eventually the trees die.

In 2010, a panel convened by the National Academy of Sciences reported that the sort of genetic engineering Mirkov and others are doing "holds the greatest hope" for creating citrus trees resistant to the bacterium. By that time greening was already confirmed in every Florida county with commercial citrus groves.

Mirkov is not alone in his pursuit. He decided early on to only work with genes from foods that are already commonly eaten. But others are pursuing research with honey bee venom, a toxin from a beetle and other compounds. Even Mirkov's backer Southern Gardens Citrus is considering other approaches, including one that would create insect-resistant trees.

Southern Gardens Citrus President Rick Kress said they're looking for trees that are not only HLB resistant, but also produce the fruit they need to be commercially viable.

"The bottom line is the citrus industry needs a solution," Kress said. "That's what's driving all of this."

The disease was confirmed in Florida in 2005 and is present in several other southeastern states and around the world, including major citrus producer Brazil. A study released earlier this year by the University of Florida's Institute of Food and Agricultural Sciences estimated the disease had cost that state's industry $3.63 billion in lost revenues since 2006.

By last year, more than 43 percent of Florida citrus trees had been infected with HLB and the rate is climbing so steeply that Jim Graham, a microbiologist at the University of Florida's Citrus Research and Education Center, expects it to double in the next year or two.

"It won't be long before Florida is 100 percent infected," Graham said. He said HLB has doubled the costs of growing citrus in Florida.

In January, researchers surveying groves in South Texas found infected orange and grapefruit trees in two groves across the street from each other about 10 miles from Mirkov's lab.

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