Although citrus greening enters trees through their leaves, University of Florida researchers have discovered that the deadly disease attacks roots long before the leaves show signs of damage – a finding that may help growers better care for trees while scientists work to find a cure.

“The role of root infection by insect-carried bacterial pathogens has been greatly underestimated,” said Evan Johnson, a research assistant scientist with UF’s Institute of Food and Agricultural Sciences.

Hundreds of researchers throughout the world are rushing to find a viable treatment for citrus greening, which is devastating Florida’s $9 billion citrus industry and has affected citrus production throughout North America.

Johnson was the lead author of a scientific paper outlining the research published in the April issue of the journal Plant Pathology. He and his fellow team members – Jian Wu, a graduate student in soil and water science, researcher Diane Bright and Jim Graham, a professor of soil microbiology – are based at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

Citrus greening first enters the tree via a tiny insect, the Asian citrus psyllid, which sucks on leaf sap and leaves behind bacteria that spread through the tree.  Johnson said the bacteria travel quickly to the roots, where they replicate, damage the root system and spread to the rest of the host tree’s canopy.  The disease starves the tree of nutrients, leaving fruits that are green and misshapen, unsuitable for sale as fresh fruit or juice. Most infected trees die within a few years.

It was originally thought that the leaves and fruit were affected first, but the team’s research found that greening causes a loss of 30 to 50 percent of trees’ fibrous roots before symptoms are visible above ground.

“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.