Amino acids in orange juice may hold the key to winning the battle against citrus greening (Huanglongbing) disease.

Researchers at the US department of agriculture’s Agriculture Research Service and the University of California-Davis used nuclear magnetic resonance spectroscopy to study the amino acid composition of juice from oranges grown on trees that tested positive for Huanglongbing (HLB) and on trees that tested negative for the disease.

ARS chemist Andrew P. Breksa and University of California-Davis professor Carolyn M. Slupsky have led the study, apparently the first to use the magnetic resonance technology which they hope will pave the way to a safe, effective, environment0 friendly approach to undermine Candidatus Liberibacter asiaticus, the microbial culprit behind HLB.

The study yielded distinctive profiles of the kinds and amounts of 11 different amino acids in three types of oranges: fruit from healthy trees; symptom-free fruit from HLB-positive trees; and fruit, with HLB symptoms, from HLB-positive trees.

With further research, the profiles may prove to be a reliable, rapid and early indicator of the presence of the HLB pathogen in an orchard, according to Breksa. He also noted that the profiles may reveal clues to mechanisms underlying the microbe’s mostly unknown mode of attack. For instance, if the HLB pathogen were causing havoc with the trees’ ability to create, use and recycle amino acids, scientists might be able to use that information as a starting point for a counter-attack strategy.

Phenylalanine may be a case in point. An orange tree can convert this amino acid into cinnamic acid, a precursor to compounds thought to be important to the tree’s defence system. But the researchers found that juice squeezed from oranges of HLB-positive trees had significantly higher concentrations of phenylalanine, which suggests that the HLB pathogen may have interfered with the tree’s conversion of phenylalanine to cinnamic acid.

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