A University of California, Davis-led research team may be on track to diagnose Huanglongbing, or citrus greening, before trees begin to show signs of infection.

Currently, the devastating citrus disease experiences a long latent phase that makes early detection difficult.

Through DNA sequencing technologies the team, directed by plant molecular biologist Abhaya Dandekar, could improve diagnostic tests and treatments.

"Because the disease has a long latent phase during which there are no symptoms of infection and the bacteria are resistant to being grown in the laboratory, the only option for halting transmission of citrus greening has been to apply chemical pesticides to control the insect that spreads the bacteria," Dandekar said.

As stands, HLB threatens the entire U.S. citrus industry, valued at US$3.4 billion in 2012, the university reported.

"Florida is seemingly in the death grip of citrus greening, and many experts believe it is just a matter of time before the disease appears full force in California," Dandekar said.

The study, published in PLOS ONE, found that the disease interferes with starch and sugar metabolism of leaves and fruit. It also weakens the plant's ability to fight off infection by disrupting its hormonal networks.

Through the study, researchers analyzed four categories of healthy and diseased citrus trees to better understand the early stages of infection.

Many of the factors normally present in plant diseases did not exist, tipping the researchers off that HLB could be causing a metabolic or nutrient imbalance.

By analyzing "transcriptome," an RNA collection found in leaves and fruit, the team found a buildup of starch in leaves. This accumulation caused blockage of nutrient transportation. They also found a metabolic disruption of sucrose, a sugar key to photosynthesis.

Additionally, the team found disruptions to several hormones that regulate the immune system, including salicylic acid, jasmonic acid and ethylene.

The research could lead to new methods of detection and short-term treatments for infected trees.

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