Researchers discover citrus greening affects roots before leaves

May 01, 2014 by Kimberly Moore Wilmoth

(Phys.org) —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 around the world are rushing to find a viable treatment for , which is devastating Florida's $9 billion and has affected 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 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.

Experts say this research is significant in the fight against greening.

"Based on the work of Dr. Johnson and his colleagues, we now know how important roots are in the development of greening disease," said Jackie Burns, director of the CREC. "We hope further investigations on the role of roots in this disease will lead to future management solutions that help growers remain productive until a permanent solution can be found."

To battle greening, UF/IFAS researchers have attempted everything from trying to eradicate the psyllid to breeding trees that show better greening resistance. While Johnson's research is not a cure, it may help more trees survive as scientists continue their search.

"We are still trying to determine how the bacteria are killing the roots," Johnson said. "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."

Johnson suggested that growers increase the acidity levels of irrigation water and soil to match the optimum pH for the rootstock (preliminary results show that this improves root density compared to untreated groves) and water more frequently for shorter periods. Those treatments are being studied by UF researchers in Lake Alfred and at the Southwest Florida Research and Education Center in Immokalee.

He added that while psyllid control is essential, growers should make careful decisions on how many resources to devote to any management strategy for greening-infected , based on their economic means, until field trials have been completed.

Explore further: Feds joins battle on citrus disease

add to favorites email to friend print save as pdf

Related Stories

Feds joins battle on citrus disease

Dec 12, 2013

The federal government is waging war against citrus greening disease, which threatens to devastate Florida's orange crop and could affect the entire nation.

Researchers find genetic cause for citrus canker

Jan 31, 2014

Researchers from the Institute of Food and Agricultural Sciences at the University of Florida are closer to finding a possible cure for citrus canker after identifying a gene that makes citrus trees susceptible to the bacterial ...

Phloem production in Huanglongbing-affected citrus trees

Mar 26, 2014

Citrus Huanglongbing (citrus greening disease) is highly destructive and fast-spreading, contributing to a reduction in crop yields in Florida and threatening the future of the citrus industry worldwide. Once infected, trees ...

Recommended for you

New study charts the global invasion of crop pests

17 minutes ago

Many of the world's most important crop-producing countries will be fully saturated with pests by the middle of the century if current trends continue, according to a new study led by the University of Exeter.

Zambia lifts ban on safari hunting

1 hour ago

Zambia has lifted a 20-month ban on safari hunting because it has lost too much revenue, but lions and leopards will remain protected, the government said Wednesday.

The devastating spread of the mountain pine beetle

8 hours ago

When the mountain pine beetle began blazing a path across forests in British Columbia and Alberta, nobody could have imagined the extent of the damage to come. But as the insect devastated pine forests and ...

User comments : 0