UC Riverside is Leading the Fight Against Citrus Greening Disease

Experts are available to discuss the spread of Huanglangbing and recent research efforts

this photo shows a healthy citrus tree at the University of California, Riverside.

A healthy citrus tree at the University of California, Riverside.

Homeowners: If you think you have a diseased trees, call: 800-491-1899. Be vigilant to control the insect pest (Asian Citrus Psyllid) that moves the pathogen. Homeowners need to apply the appropriate pesticides in September when new leaves are emerging and roots are growing. More information specifically for Riverside residents can be found at the county agriculture commissioner’s website (http://www.rivcoawm.org/).

A list of helpful links and a Q&A for homeowners are available on UCR’s College of Natural and Agricultural Sciences website.

RIVERSIDE, Calif. (www.ucr.edu) — With the recent discovery of Huanglongbing (HLB, also called citrus greening disease) on a tree in Riverside, the spread of this deadly bacterial disease continues in California. The bacteria, which is carried by a tiny insect called the Asian Citrus Psyllid, has already decimated citrus groves in Florida and elsewhere.

Building on many years of research efforts, experts in the University of California, Riverside’s College of Natural and Agricultural Sciences (CNAS) have been working with government and industry officials to address the disease and keep it from spreading.

a ohoto showing how HLB affects citrus leaves.

An early symptom of Huanglongbing is the yellowing of leaves on an individual limb. Wikimedia Commons

Ongoing research efforts include breeding plants for resistance, developing molecular tools to combat this disease, new treatment programs using insecticides and bactericides, and early disease detection techniques. In the short term, UCR is developing techniques to increase citrus production and overall health to give the industry a boost.

Recent research highlights include:

  • In 2016, in collaboration with the citrus industry, UCR began building a containment facility to work with the disease and expedite research progress.
  • In March of 2017, a group of UCR researchers received a $5,112,000 five-year grant from the US Department of Agriculture’s (USDA) National Institute of Food and Agriculture in the fight against HLB, the largest grant in the nation to fight HLB.
  • In June of 2017, the California Citrus Research Foundation broke ground on a research facility in Riverside to conduct HLB related research. This facility will be operated by UCR.

    A photo of how Huanglongbing affects mandarin oranges by preventing them from ripening.

    Huanglongbing on mandarin oranges. Wikimedia Commons

UCR experts who can speak about HLB include:

Tracy Kahn, Curator of UCR’s Citrus Variety Collection

Contact: tracy.kahn@ucr.edu, (951) 827-7360

Tracy Kahn is the curator of UCR’s Citrus Variety Collection, one of the world’s most diverse living collections of citrus and related types with approximately 1,000 different varieties, including mandarins, blood oranges, navel oranges, citrons, clementines, tangors, grapefruit, Valencia oranges, and pummelos. She conducts research evaluating the commercial potential of new citrus varieties and provides various extension activities on citrus for the industry and the public.

Peggy Mauk, Director of Agricultural Operations, College of Natural and Agricultural Sciences

Contact: peggy.mauk@ucr.edu, (951) 827-4274

Peggy Mauk researches abiotic or biotic stresses to subtropical fruit crops, such as avocado, citrus, dates and mangos. As director of agricultural operations, she oversees field research in support of the mission of the College of Agriculture and Natural Sciences.

“UCR continues to provide research results that support the California Citrus Industry and beyond. Now that HLB is in Riverside there is fear of devastation. For example, Florida has only approximately 30 percent of production compared to 10 years ago, but there is hope for the future.”

Georgios Vidalakis, Professor & UC Extension Specialist in Plant Pathology; Director of the Citrus Clonal Protection Program

Contact: georgios.vidalakis@ucr.edu, (951) 827-3763

As the director of UCR’s Citrus Clonal Protection Program, Georgios Vidalakis is working to ensure HLB and other exotic citrus diseases do not enter California via propagative plant materials. The CCPP has been the gatekeeper in excluding lethal citrus diseases, such as HLB, from entering and spreading in California since 1956.

In addition, the CCPP is part of the National Clean Plant Network for Citrus, which produces, maintains, and distributes clean citrus germplasm/budwood throughout the U.S.

“The CCPP online budwood distribution system has over 1,365 registered users and we are inviting every citrus enthusiast in California and U.S.A. to join our HLB free budwood community.”

Vidalakis’ work has created a pathway that allows for the safe movement of critical citrus germplasm from Florida into California.

“Citrus breeders in Florida have been unfortunate in having been flooded with HLB. Many hybrids were lost, but through the years trees that appear to tolerate the disease a little better than others started to appear. The CCPP has received California citrus industry and federal funding to introduce hundreds of these trees into California to evaluate their potential use as commercial citrus varieties or parents of varieties that may be HLB tolerant.”

Hailing Jin, Professor & Cy Mouradick Endowed Chair, Microbiology and Plant Pathology; Director, Genetics, Genomics and Bioinformatics Graduate Program

Contact: hailingj@ucr.edu, (951) 827-7995

Hailing Jin’s work aims to stop the spread of HLB through several approaches. These include generating HLB-resistant/tolerant citruses by boosting citrus immune systems, and identifying and applying antimicrobial molecules on citrus to kill and inhibit the bacterium that causes HLB.

Wenbo Ma, Professor of Plant Pathology

Contact: wenboma@ucr.edu, (951) 827-4349

Wenbo Ma, a professor of plant pathology, is studying the disease at a molecular level. Understanding how HLB occurs will identify ways to stop it from killing citrus trees and develop varieties that are resistant to the disease. Her research has also led to the identification of molecular markers that can be used for HLB detection.

Philippe Rolshausen, Cooperative Extension Specialist

Contact: philrols@ucr.edu; (951) 827-6988

Philippe Rolshausen, a cooperative extension specialist, works on citrus microbiome and citrus undercover production systems (CUPS) as huanglongbing management strategies. He is evaluating how cultural practices impact microbial communities associated with citrus trees and plant health. In addition, he is exploring growing citrus trees under a sealed protective screen to exclude the insect vector (the Asian Citrus Psyllid) that transmit the bacteria causing citrus huanglongbing.

Mikeal Roose, Professor of Genetics

Contact: mikeal.roose@ucr.edu, (951) 827-4137

Mikeal Roose, a professor of genetics, is developing citrus varieties with resistance or tolerance to the disease. Resistance (few or no bacteria in trees) is preferable to tolerance (trees remain relatively healthy when infected with bacteria), but varieties with resistance are more difficult to develop.  With Chandrika Ramadugu at UCR and other colleagues, the researchers found resistance and tolerance in citrus types originating in Australia. Research is in progress to identify the genes responsible for resistance, including determining DNA sequences of resistant types and studies of citrus and bacteria gene expression during infection.

“Developing HLB resistant citrus is the greatest challenge of my career because the disease is difficult to detect at early stages of infection, and because sources of resistance are very different from most citrus that we grow and consume, but we can be hopeful because we have powerful new genomics tools that make breeding more precise and predictable.”

Caroline Roper, Assistant Professor and Assistant Plant Pathologist

Contact: carolyn.roper@ucr.edu, (951) 827-3510

Caroline Roper’s group is investigating the role the citrus microbiome plays in tree health with the goal of leveraging this information to discover natural microbial products that can be used as antimicrobials to combat HLB. In addition, in collaboration with faculty in the Bourns College of Engineering, her group is studying the pathways those antimicrobial travel inside citrus trees.


About UCR’s Citrus Variety Collection

The Citrus Variety Collection at UCR, with its 1000 different citrus and citrus types, is one of the premier collections of its kind in the world. It also supports the needs of the citrus industry, which is a critical part of the California economy and beyond. With the recent discovery of HLB in Riverside, it is more urgent than ever to preserve this one-of-a-kind collection. UCR is in need of funds to build structures to protect the Citrus Variety Collection from HLB and other diseases and pests. Please consider making a donation.

Media Contact


Tel: (951) 827-4580
E-mail: sarah.nightingale@ucr.edu
Twitter: snightingale

Additional Contacts

Bryan Schneider, Director of Communications, College of Natural & Agricultural Sciences
Tel: (951) 827-5304
E-mail: bryan.schneider@ucr.edu

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