What a coincidence it might be to find the prevention for the deadly citrus greening disease inside the fruit itself!

Researchers at the U. S. Department of Agriculture’s Agricultural Research Service (ARS) in cooperation with their fellow members at the University of California think this is a distinct possibility. So far it’s a possibility that has been only quietly explored.

Also part of the investigative team are researchers attached to the Citrus Research Board, an industry supported organization in Visalia, near the heart of the Central California citrus empire.

ARS researcher Andrew Breksa III, working at the USDA’s Bay Area facility in Albany, said the profiles of amino acids in oranges may prove to be “a reliable, rapid and early indicator of the presence of the HLB pathogen in an orchard.”

“Citrus greening disease” has become the easier-to-say synonym for huanglongbing or HLB, the killer disease carried by the even harder to pronounce microbe Candidatus Liberibacter asiaticus. It has killed a large percentage of citrus trees in Florida, devastating the industry there, and threatens orange, lemon, grapefruit and other citrus trees in California.

Much attention has been given to the Asian citrus psyllid (ACP), which carries the disease, and has been found in profusion in Southern California and sparsely in a few Central California orchards. Quarantines, with restrictions on handling and shipping of fruit have followed detections of the ACP, causing growers and packinghouses to undergo extra inspection, sanitation and handling procedures.

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Breksa and colleague Carolyn Slupsky at UC Davis have discovered that the amino acid composition in fruit from HLB infested trees differs from that of clean trees. They discovered the differences by using nuclear magnetic resonance spectroscopy (easy for them to say) to analyze juice from oranges grown on HLB-positive trees and HLB-negative trees.

Breksa said the finding is important because HLB can be a silent killer, living in trees for years before it gains the upper hand and causes ultimate decline and death. Knowing of its presence allows growers to take early steps to remove diseased trees from their orchards.

He said the profiles of amino acids have led to another use as well, possibly revealing clues to mechanisms behind the mode of attack used by the microbes.  So far, researchers and plant pathologists have been mystified by HLB’s ability to overcome the natural resistance offered by citrus trees when they are under such siege.

Breksa points out that trees need amino acids to grow, develop and defend against disease, but he suggests that the HLB pathogen might be causing havoc with the trees’ ability to create, use and recycle the amino acids. HLB seems to find a way to bypass this natural disease resistance feature of the fruit.

UC Riverside, where a huge quantity of research on citrus has been done through the years, is not directly involved in the amino acid exploration that Breksa and Slupsky are conducting, but it is aware of it, and certainly interested in it.

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