Texas A&M plant pathologist Erik Mirkov is fine tuning a transgenic process that could help the citrus industry survive its worst scourge, the disease Huanglongbing (HLB).

Over the last six years, Mirkov, based at the Texas A&M AgriLife Research and Extension Center in Weslaco, has inserted multiple protein genes called definsins - found in spinach - into young citrus plants to create transgenic trees which act as a protective shield against HLB.

“Our greenhouse tests with spinach definsins in citrus trees reveal either complete immunity to HLB or extremely high resistance to the devastating disease,” Mirkov said.

Mirkov explained his research during the 2013 joint meeting of the Caribbean and Pacific divisions of the American Phytopathological Society held in Tucson, Ariz., in June.

A definsinis a natural protein found in all plants, insects, and mammals, including humans.

In the human body, definsins are part of its pre-formed defense system to keep microorganisms (bacteria and fungi) from causing infection. Defensins are found in tears and mucous, and circulate through the blood stream.

HLB is a major problem in all citrus-growing regions in the world, including most recently the U.S. The disease was found in Florida in 2005 and has spread to almost all citrus-growing regions in the Sunshine State.

HLB has spread westward, found in several Texas commercial citrus groves early last year. A single case of HLB was found in California last year in a residential citrus tree in the Los Angeles area. HLB has not been identified in Arizona citrus.

HLB is caused by the bacteria Candidatus Liberibacter which is vectored to citrus trees by the Asian citrus psyllid.

While HLB research is ongoing worldwide, there is no known cure. Every HLB-infected tree eventually dies. Fruit from infected trees become misshapen and the flavor turns sour, leading to unmarketable fruit.

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Mirkov conducts his lab research in Weslaco. The transgenic tree greenhouse and field tests are underway at Southern Gardens Citrus, a citrus grower and processor in South Florida.

The tests include a screened psyllid greenhouse where large numbers of infected psyllids fly and land on the transgenic citrus plants, at much higher insect numbers and infection odds than a commercial grower would ever find in a grove.