UCR wages $11+ million war against citrus greening disease
Three projects win funding to fight tree-killing bacteria
With three new grants totaling more than $11 million, UC Riverside is helping lead the fight against citrus greening or Huanglongbing, a disease threatening citrus industries in the U.S. and worldwide.
The disease is from bacteria transmitted to citrus trees by a tiny flying insect, the Asian citrus psyllid. Infected trees produce no fruit, or fruit that is bitter, small and worthless. Despite intensive research for the past 15 years, there is no known cure for it. It has reduced citrus production in Florida by more than 75%, and it has already been detected in Texas and California.
Because California supplies the country with 80% of its fresh citrus, and because 267,000 acres of Golden State lemons, oranges, grapefruits, and mandarins are at stake if operations are permanently lost, the USDA National Institute of Food and Agriculture is making an emergency investment in citrus disease research with three projects at UCR.
These projects focus on instilling tolerance to the disease with three different approaches: below ground, in the rootstocks, above ground in the shoots and branches, and systemically, with a peptide that would move throughout the tree.
The largest of the projects, at $6.8 million, is being led by Danelle Seymour, assistant professor of genetics in the Botany and Plant Sciences Department at UCR. Their focus is on breeding Huanglongbing or HLB-resistant rootstocks, and the project depends on collaboration with Kim Bowman, a citrus breeder at the USDA Agricultural Research Service in Ft. Pierce, Florida.
“In Florida, nearly every single tree is infected. It's terrible for growers, but wonderful for breeding,” Seymour said. “We can't do this research at large scale in California because the disease isn't as widespread here.”
The classic way to improve resistance or encourage new qualities in crops is through genetics, making crosses between one plant that has a favorable trait, and one that doesn't. “We hope the result is better than the parents,” Seymour said. “When you work in wheat or tomato, you can do these crosses and perform evaluations every year. In citrus, it takes 10 - 15 years to evaluate a new generation of trees.”
Because of the long lag time, the research-ready trees in Florida represent an opportunity for Seymour's team to begin examining new crosses now. The breeder, Kim Bowman, has evaluated over 10,000 trees and unique hybrids, from which a handful will be selected for release to growers.
In addition to evaluating these select few new hybrids for their HLB tolerance, the researchers will be watching the Florida-grown trees' responses to the different environmental conditions in California. “Can they perform well in response to different salinity levels in the soil, different humidity, as well as other pests and pathogens that we have here? We'll find out,” Seymour said.
Chandrika Ramadugu, a project scientist also in UCR's Department of Botany and Plant Sciences, is leading a project to develop HLB-resistant scion varieties that can be grafted to rootstocks. A scion is an above-ground portion of a plant, such as a bud or shoot, that can be used for grafting.
For trees, grafting can be equated to an organ transplant. The scion from one tree is attached to the trunk or rootstock of another with the hope of creating a new plant with combined attributes.
With its grant of $3.28 million, this project will analyze second-generation hybrids that are bred for ten years using Australian lime as a source of disease resistance.
Ramadugu will evaluate 24 novel hybrids in California, Florida, and Texas to assess resistance to HLB. Ideally, in addition to having enhanced disease tolerance, the new plants will also be able to produce good-tasting fruit.
There is little genetic diversity in cultivated citrus. When new pathogens arrive, the genetic uniformity can result in disease epidemics and dire consequences for the crop. In addition to the potential benefits of this project for the fight against HLB, the new hybrids may also help protect citrus from other pests and pathogens.
A third project, granted $1.36 million, will utilize a peptide found in Australian finger limes that is known to impart HLB resistance. Led by Hailing Jin, Microbiology & Plant Pathology professor, the project is developing ways to infuse trees with the peptide.
“The antimicrobial peptide in the finger limes are more efficient at killing bacteria as compared to antibiotics currently used in the field, and much more stable at high temperatures,” Jin said.
Because spray applications are expensive, Jin's project aims to spread the peptide throughout the trees' insides. In collaboration with University of Florida professor Svetlana Folimonova, Jin's team utilizes a natural citrus virus with almost no symptoms to deliver the peptide into the trees.
“You infect the tree with the virus, and it will spread in areas where the bacteria reside,” Jin said. “It would move systemically through the tree, and it would be very cost efficient for growers. No need to buy more insecticides.”
These grants were enabled by the 2018 Agricultural Improvement Act, which authorized the Emergency Citrus Disease Research and Development Trust Fund to fight HLB. With these and other projects, the USDA is bringing together the nation's top scientists to find scientifically sound solutions to the problem in a financially and ecologically sustainable way.
Citrus growers in Santa Barbara County and the surrounding area are invited to attend the upcoming Santa Barbara County Citrus Industry Workshop on December 8, from 9 to 11 a.m. The workshop will be held at the Santa Barbara County Air Pollution Control District Building, located at 260 North San Antonio Road, Suite A, Santa Barbara. There is no cost to attend, but registration is required.
Registration spots are limited. To secure your spot in the workshop, please RSVP to CPDPP Grower Liaison Cressida Silvers at cressidasb@gmail.com, or call 805-681-5600 for more information.
In cooperation with the California Department of Food and Agriculture, the California Citrus Pest and Disease Prevention Program and the Santa Barbara County Agricultural Commissioner's office, this free in-person workshop will be focused on connecting with growers, PAC/QAC/QAL/PCA holders and farm labor contractors in the Santa Barbara County area to discuss a variety of topics that are currently impacting the citrus industry.
Topics of the workshop will include the most recent updates on Huanglongbing (HLB) detections in Ventura County and new changes to HLB quarantine regulations. An update on exotic fruit fly quarantines in southern California will also be presented. 1.5 CEUs will be available.
Questions? Email Cressida Silvers at cressidasb@gmail.com, or call 805-681-5600, for more information and to RSVP.
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So what causes these wounds on leaves and fruit on lemons? Corky, sunken blisters on the leaves. Small divots in the fruit. Some of the spots had halos around them, but most not. That would indicate an infection of some sort. It was showing up in a large orchard near Santa Paula.The growers indicated that maybe 20% of the fruit was affected.
Insects? None. Disease? Not really. More damage was on the fruit than leaves, but what would cause what looked like mechanical damage like this? Outside fruit and mostly on the outside of the outside fruit. Wind poking stems? Frost heave? Hail?
Looking round the area at other orchards, other owners, other management practices, old trees and new. The whole area had the problem and it was only on lemons. It wasn't on opuntia cactus or some nearby avocados, oleanders, or roses. But it was something real and it was something that had happened in that area. Rain. High humidity. Things we don't normally see here in the summer time. And what do we get - Edema. Cell Burst. Mesophyll Collapse.
Edema may be caused by any agent that stimulates an abnormal increase in the size and number of a group of inner cells. Edema can be induced by (1) spraying with some chemicals such as ammoniacal copper carbonate in an oil emulsion, (2) injuries resulting from wind-blown sand particles and sucking insects, (3) high light intensity, and (4) accumulation of water in the intercellular spaces.
The most common cause of edema is the presence of abundant, warm soil water and a cool, moist atmosphere. Under these conditions the roots absorb water at a rate faster than is lost through transpiration. Excess water accumulates in the leaf, some parenchyma cells enlarge and block the stomatal openings through which water vapor is normally released from the plant; thereby contributing to further water retention in the leaf. If this condition persists, the enlarged cells divide, differentiate a cork cambium, and develop elongate cork cells externally to form a periderm. The rupture of the epidermis by the enlarged inner cells and the periderm account for the raised, crusty appearance of older edema spots and also corky veins.
So what can a lemon grower do? Especially since more rain is forecast for this coming year.
1. Avoid irrigation or watering during cool, overcast humid weather. Irrigate when soils need to be watered. Avoid a fix schedule and when humidities are high.
2. Avoid overfertilizing, especially when the plants are growing slowly, such as during the winter months. Maintain fertility based on a leaf analysis. Avoid low levels of potassium and calcium.
Photo:
Early on, the black spots on the fruit start out as a clear exudate. The same for the brown spots on the leaves.
UC IPM supports research and extension programs in integrated pest management (IPM). UC Agriculture and Natural Resources scientists adapt research for practical application, and Cooperative Extension advisors and specialists develop and deliver IPM programs to a variety of clientele, including professional pest managers, growers, residents, and agencies. UC IPM staff work with UC ANR scientists to develop "how-to" materials that help the clientele carry out programs and solve pest problems.
To complement the extension programs, UC IPM staff members coordinate development of a variety of materials that explain how to carry out pest management tactics and strategies. Working with UC ANR experts, program staff produce and maintain an extensive array of print and Web-based publications, databases, training materials, and interactive tools for decision making.
Examples are the pest management guidelines and a home and landscape database of pest solutions for residential audiences, IPM manuals for specific crops, books about IPM in landscapes and gardens, a variety of books on pesticide safety, and an extensive weather database that supports interactive pest models.
And now they are happy to announce the publication of a new update to the Citrus PMG. The Year-Round Program has been updated, Ants, Asian Citrus Psyllid, and Huanglongbing
And to learn more about Ant control in citrus, cherimoya and passion fruit, look into the upcoming workshops, September 19 and 21:
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