Citrus greening disease has slashed citrus production in the state by 75 percent – August 28, 2023

(AG Insider) Since it was confirmed in Florida 25 years ago, citrus greening disease has slashed citrus production in the state by 75 percent and infected trees in Louisiana, Texas, and California. USDA researchers said on Thursday they have found a potential remedy that boosts a citrus tree’s natural resistance to disease, including citrus greening.

Their approach is directed toward new stock, raised in tree nurseries for sale to citrus growers. Research geneticist James Thompson of the Agricultural Research Service (ARS) said he envisioned the technology being transferred to nurseries so they could offer disease-free trees to farmers. “There are already a series of genes that can detect and fight [citrus greening]. The biggest problem is how to distribute the solution,” he said.

Citrus greening, a devastating plant disease, is spread by a tiny insect, the Asian citrus psyllid, that feeds on citrus leaves and stems. The bacterial disease slowly kills the tree and results in green, bitter, and misshapen fruit unsuitable for sale. Growers commonly remove infected trees and try to kill the insects in an effort to stop the spread of the disease.

Researchers at the ARS Crop Improvement and Genetics Research unit in Albany, California, discovered a way to augment a citrus tree’s natural resistance to pathogens by incorporating receptors that recognize the pathogens and activate disease fighting responses. They employed agro bacteria, sometimes called nature’s genetic engineer, to help introduce the new material.

“Essentially, you clone the DNA of interest [with resistance to citrus greening] and add it to agro bacteria, then the agro bacteria adds that specific bit of DNA to the genome,” Thompson said in an ARS release. “A bit of the original plant is cut into little pieces and mixed temporarily with the agro bacteria. The plant pieces are then cleaned of agro bacteria and encouraged to grow into a whole plant.”

California replaced Florida as the No 1. orange producer in the wake of citrus greening disease and adverse weather this season, with a harvest of 1.76 million tons of oranges, compared to 714,000 tons in Florida. In the 2021-22 season, Florida grew 1.85 million tons of oranges. Production collapsed this season following a freeze in January 2022 and hurricane damage in September 2022. Florida produced 3.2 million tons of oranges in the 2018/19 season.

In related work, scientists at Florida International University are investigating whether natural compounds in citrus plants can suppress or even eliminate the bacteria that causes citrus greening. “The bacteria inside an infected citrus plant needs to be killed or its population significantly reduced to minimize the symptoms and help the tree to survive,” said associate professor Kateel Shetty earlier this year.

FIU research has suggested that microorganisms called endophytes could be used for disease management of citrus greening. The USDA awarded $500,000 to FIU to explore the idea.

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