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- Psyllids often get into groves unseen and go unnoticed while building up their population. By the time they're detected, they have adapted well, populations have exploded and transmission of the bacteria to the trees has already occurred.
"Citrus greening disease has become a national problem," Brown said. "We have been aware of this disease for quite some time. The pathogen itself has been found in almost all citrus growing regions of the world."
Brown explained that while it took the psyllid insect pests 30 to 40 years to spread from the original introduction area in the southerly Americas, the pathogen was introduced multiple times through citrus tree cuttings grafted onto existing trees, a common practice commercial growers and gardening enthusiasts apply to improve the quality or quantity of fruit. In the U.S., the Asian citrus psyllid first appeared in Florida in 1998.
Before growers and home owners realized that the pathogen spreads by the psyllid insects, it was common to simply take out an infected tree and destroy it without too much economic consequence, Brown explained. This changed in August 2005, when Liberibacter was found in Florida for the first time.
"From that point, they monitored the disease and discovered that it was moving westward from Florida and possibly also northward from Mexico toward Texas, Arizona and California," Brown said. "Right now, Arizona is only state in which the psyllid has been found but not the bacterium."
Once the psyllid was found carrying the bacterium in Florida, the risk of infection leading to transmission and incidence of disease skyrocketed, she added.
According to Brown, psyllids often get into groves unseen and go unnoticed while building up their population. By the time they're detected, they have adapted well, populations have exploded and transmission of the bacteria to the trees has already occurred.
"Eradication is not an option at this point," she said. "We have to learn how to live with this disease and the psyllid that transmits the pathogen. In Arizona, citrus is an important crop commercially, but also to many homeowners and urban public-use areas. Many of us love to have our citrus trees in the yard."
"Our research aims at disarming the psyllid to disable it to transmit the bacterium," Brown said. "If we can eliminate its ability to transmit the pathogen, it becomes just a pest, and no longer a carrier of a deadly plant disease."
"Specifically, we identify and study the proteins involved in the bacteria's various life cycle processes," explained Brown, who has been working for three years studying a potato psyllid as a model organism. "From the time they set up shop inside the insect's gut until they multiply and finally relocate to the mouth parts, from where they enter a citrus plant."