The role of root infection in Huanglongbing-contaminated citrus trees appears to be much greater than scientists previously thought.

Little is currently known about how Candidatus Liberibacter' spp., the bacteria that causes greening, spreads throughout a plant's system. University of Florida researchers have found some initial clues, however, that point to the vital role of the host's root system.

Although HLB, also known as citrus greening, first appears on damaged plant leaves, the UF team found that the disease begins long before its visible appearance on foliage.

Liberibacter asiaticus, the psyllid responsible for HLB bacterial spread, was found to preferentially colonize roots before leaves, where the insect then multiplied and invaded foliage.

The research indicates that greening may causes losses of 30% to 50% of trees’ fibrous roots before showing symptoms above ground.

The insight into the disease's initial development could help guide future management techniques, explained Evan Johnson, the lead author of the study and a research assistant scientist with UF’s Institute of Food and Agricultural Sciences.

"The role of root infection by insect-carried bacterial pathogens has been greatly underestimated," Johnson said in a press release.

"This early root loss means that the health of a citrus tree is severely compromised before the grower even knows it is infected."

Johnson said the team is still investigating how exactly the disease infects and weakens citrus roots. He encouraged growers to prioritize root health by maintaining optimum pH for rootstock and watering frequently in shorter increments.

"This finding suggests that growers should focus more effort on maintaining the health of the root system in relation to other soilborne pests and overall soil quality to maintain as much of the root system as possible," he said.

The study was published in the April issue of Plant Pathology.

Related stories: U.S.: new Florida cultivars show citrus greening tolerance

U.S. Congress directs funding to fight HLB

Florida citrus growers cross fingers for greening solution

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