California Ag Network

Tag: HLB

  • Novel Treatment Causes Killer Citrus Disease to Leak & Die

    New research affirms a unique peptide found in an Australian plant can destroy the No. 1 killer of citrus trees worldwide and help prevent infection. Huanglongbing, HLB, or citrus greening has multiple names, but one ultimate result: bitter and worthless citrus fruits. It has wiped out citrus orchards across the globe, causing billions in annual production losses.

    Untreated citrus plants on the left, as compared to treated ones on the right. (Hailing Jin/UCR)

    All commercially important citrus varieties are susceptible to it, and there is no effective tool to treat HLB-positive trees, or to prevent new infections. However, new UC Riverside research shows that a naturally occurring peptide found in HLB-tolerant citrus relatives, such as Australian finger lime, can not only kill the bacteria that causes the disease, it can also activate the plant’s own immune system to inhibit new HLB infection. Few treatments can do both.

    Research demonstrating the effectiveness of the peptide in greenhouse experiments has just been published in the Proceedings of the National Academy of Sciences.

    The disease is caused by a bacterium called CLas that is transmitted to trees by a flying insect. One of the most effective ways to treat it may be through the use of this antimicrobial peptide found in Australian finger lime, a fruit that is a close relative of citrus plants.

    “The peptide’s corkscrew-like helix structure can quickly puncture the bacterium, causing it to leak fluid and die within half an hour, much faster than antibiotics,” explained Hailing Jin, the UCR geneticist who led the research.

    When the research team injected the peptide into plants already sick with HLB, the plants survived and grew healthy new shoots. Infected plants that went untreated became sicker and some eventually died.

    Arrows point to areas of fluid leakage from the bacterial cell after treatment with the antimicrobial peptide. (Hailing Jin/UCR)

    “The treated trees had very low bacteria counts, and one had no detectable bacteria anymore,” Jin said. “This shows the peptide can rescue infected plants, which is important as so many trees are already positive.”

    The team also tested applying the peptide by spraying it. For this experiment, researchers took healthy sweet orange trees and infected them with HLB-positive citrus psyllids — the insect that transmits CLas.

    After spraying at regular intervals, only three of 10 treated trees tested positive for the disease, and none of them died. By comparison, nine of 10 untreated trees became positive, and four of them died.

    In addition to its efficacy against the bacterium, the stable anti-microbial peptide, or SAMP, offers a number of benefits over current control methods. For one, as the name implies, it remains stable and active even when used in 130-degree heat, unlike most antibiotic sprays that are heat sensitive — an important attribute for citrus orchards in hot climates like Florida and parts of California.

    In addition, the peptide is much safer for the environment than other synthetic treatments. “Because it’s in the finger lime fruit, people have eaten this peptide for hundreds of years,” Jin said.

    Hailing Jin, research leading UC Riverside geneticist

    Researchers also identified that one half of the peptide’s helix structure is responsible for most of its antimicrobial activity. Since it is only necessary to synthesize half the peptide, this is likely to reduce the cost of large-scale manufacturing.

    The SAMP technology has already been licensed by Invaio Sciences, whose proprietary injection technology will further enhance the treatment.

    Following the successful greenhouse experiments, the researchers have started field tests of the peptides in Florida. They are also studying whether the peptide can inhibit diseases caused by the same family of bacteria that affect other crops, such as potato and tomato.

    “The potential for this discovery to solve such devastating problems with our food supply is extremely exciting,” Jin said. — By Jules Bernstein, UC Riverside

  • First CLas-Positive Asian Citrus Psyllid Found in San Diego

    An Asian citrus psyllid (ACP) sample – confirmed positive for Candidatus Liberibacter asiaticus (CLas), the bacteria that causes Huanglongbing (HLB) – was collected from a residential property in the Fallbrook area of San Diego County. Confirmed by Citrus Research Board’s Jerry Dimitman Laboratory, this adult psyllid sample is the first CLas-positive ACP found in San Diego County.

    While the first confirmation of a CLas-positive ACP in San Diego County is concerning, as of today, HLB has not been detected in any San Diego County trees but surveying and sampling of area trees is ongoing. This find signals a critical time for homeowners and growers alike to continue to control ACP populations to stop the potential spread of this deadly disease, as oftentimes a CLas-positive ACP precedes the detection of an HLB-positive tree.

    The HLB quarantine zone will not be expanded as a result of this CLas-positive ACP detection and CDFA staff is swiftly conducting surveys and collecting samples from HLB host plants that are located within a 250-meter radius around the find, per the ACP/HLB Action Plan.

    While treatment is not mandatory for area commercial growers as a result of the detection, San Diego County commercial growers who have additional questions can contact Sandra Zwaal, San Diego County Grower Liaison, at szwaal2@gmail.com.

    CLICK HERE for additional information from Citrus Pest and Disease Prevention Program (CPDPP) Citrus Insider.

    Source: Citrus Pest and Disease Prevention Program (CPDPP) Citrus Insider

  • Stay Vigilant with Asian Citrus Psyllid Finds on the Rise

    In the past few months, we have seen sporadic Asian citrus psyllid (ACP) detections popping up across California. While the citrus industry’s efforts have thus far kept Huanglongbing (HLB) out of commercial groves, these recent ACP detections are a reminder that we cannot let our guard down. The most effective way to prevent the spread of HLB is to keep psyllids out of our orchards.

    After ACP detections in multiple counties (Kern, Madera, San Luis Obispo, Santa Barbara, Santa Clara, Tulare, Contra Costa and others) were confirmed earlier this fall — including areas with historically low ACP activity — the Citrus Pest & Disease Prevention Committee is encouraging all growers to stay informed, scout for ACP and treat when advised.

    The recommendations outlined in the Voluntary Grower Response Plan, developed collaboratively by growers and scientists, represent the most effective tools known to the citrus industry at this time and are meant to supplement the California Department of Food and Agriculture’s required regulatory response. You can help prevent the spread of ACP by following these best practices, participating in recommended winter treatments and ensuring haulers and transporters are tarping loads.

    While we should expect to see this type of “flare up” occasionally, we need to remain vigilant – even when things are quiet – to ensure we continue to stay on top of this elusive pest and the dangerous disease it spreads. The upfront cost to manage ACP is much less than the potential hit to our industry if HLB spreads throughout the state. To date, HLB has only been identified in backyard citrus trees in Los Angeles, Orange, Riverside and San Bernardino counties, and hasn’t made its way into a commercial citrus grove yet. To keep HLB out of commercial citrus, psyllid control is especially critical this season with warmer weather encouraging more pests.

    Here is what you can do:

    • Follow the best practices outlined in the Voluntary Grower Response Plan for Huanglongbing
    • Participate in treatment strategies recommended by the University of California (UC)
    • Adhere to tarping regulations that help keep pests from hitching a ride to new areas of the state

    Visit citrusinsider.org for more information and resources on the voluntary grower best practices, tarping regulations and UC treatment recommendations.

    Questions?
    Contact your regional grower liaison for the latest information on detections near you and coordinated or area-wide treatment schedules. Find your grower liaison here.

    Let’s work together to protect California citrus for your businesses, neighbors and generations to come.

    Sincerely,
    Jim Gorden
    Chair, Citrus Pest & Disease Prevention Committee

  • Root Bacteria Could Help Defeat Fatal Citrus Disease

    A UC Riverside-led team is looking at tiny underground microorganisms for a way to prevent a huge problem — Huanglongbing, a disease with no cure that has decimated citrus orchards worldwide.

    The disease, also known as HLB or citrus greening, has multiple names but the same ultimate result: bitter and worthless citrus fruits. By some estimates, the end of citrus orchards in California and Florida could amount to $14 billion in lost commercial revenue.

    Fruit affected by Huanglongbing. (UCR)

    “Often times, it is thought of as an above-ground disease of the fruits, leaves, and stems,” said Caroline Roper, plant pathology professor and director of the new research effort. “However, we have seen the roots of trees decline with infection, and we want to understand why.”

    The National Institute of Food and Agriculture has awarded the UCR-led team $10 million over the next five years to investigate the role of soil and root microbes in the disease.

    Roper said data from previous studies shows the microbiome of the infected tree — which includes bacteria and fungi as well as protozoa and viruses — plays a role in the disease.

    “We have seen a shift in the root microbiome as trees get sicker,” she said.

    The microbiomes shift to contain more potentially parasitic organisms that may act as secondary invaders to a tree that is suffering from HLB, according to Roper. The invasion of these root pathogens may be causing trees to die faster when they have HLB.

    Part of this new research effort will test whether soil amendments like manure and compost might suppress parasitic microorganisms in the roots as well as the soil, and give the trees more strength to combat diseases including HLB.

    In addition, the research team will try to determine the molecular basis of HLB resistance shown by citrus root stocks developed in Florida. They’ll then see how those rootstocks perform in California, which has different soil and climate conditions.

    The research team will examine both younger trees, because a lot of citrus growers have had to re-plant their orchards after infection, as well as older trees to see if mature groves can recover.

    It will also be important to note how well root stocks from Florida, where there has been a heavy infestation of HLB, perform in California, where much less of the disease has been detected.

    “One of the great things about this grant is that we’re able to leverage existing field trials being done by our collaborators in Florida and at the UC’s Lindcove Research and Extension Center in central California,” Roper said. “This may lead to faster results than we’d otherwise have had.”

    Collaborators on the project include UC Davis; California State University, Sacramento; the University of Florida; and the U.S. Department of Agriculture’s Agricultural Research Service in Ft. Pierce, Florida. — By Jules Bernstein, UC Riverside

  • $45 Million in Funding for Citrus Research Awarded

    A total of $45 million in funding for citrus research during the 2020-21 fiscal year was awarded by the United States Department of Agriculture National Institute of Food and Agriculture (USDA-NIFA) Emergency Citrus Disease Research and Extension (ECDRE) Program. The ECDRE Program addresses priorities identified by the Citrus Disease Sub-Committee of the National Agricultural Research, Education, Extension, and Economics (NAREEE) Advisory Board by sponsoring research projects designed to provide solutions to the U.S. citrus industry. For the 2020 fiscal year, the ECDRE program selected 12 projects to receive awards.

    With funding support from the Citrus Research Board (CRB), Pepsi Co and Coca-Cola, and a consortium led by the Citrus Research and Development Foundation (CRDF), NIFA awarded a $10 million grant for their on-going coordinated agricultural project with Bayer Crop Science. The project seeks to identify and develop therapeutics for HLB and the presumed HLB pathogen ‘Candidatus Liberibacter asiaticus’ (CLas). Researchers are investigating synthetic and microbial therapeutics for further characterization and optimization, intending to develop therapeutics for commercialization.

    According to the CRB President, Marcy Martin, “Success with this project will help all citrus growers, not just those from a particular state. We like that CRDF and CRB were able to team up on this worthy project.”

    Among this year’s awardees, three current and past CRB-funded California researchers from the University of California were awarded $12.5 million between three projects. CRB-funded researcher Chandrika Ramadugu, Ph.D., was awarded $4.7 million to lead efforts to evaluate novel citrus hybrids for tolerance/resistance to HLB in multi-state field trials in California, Texas, and Florida. Caroline Roper, Ph.D., received $6.5 million to unravel the underlying mechanisms of tree health in HLB impacted groves and develop a set of best practices for extending the life and productivity of citrus groves. Past-funded CRB researcher Yen-Wen Kuo, Ph.D., was awarded $1.41 million to explore utilizing insect-specific viruses to manipulate the Asian citrus psyllid (ACP) and its associated microbes to limit psyllid activity and disease spread potentially.

    CRB-funded researchers Vivian Irish, Ph.D., from Yale University, Anne Simon, Ph.D., from the University of Maryland, and Robert Shatters, Ph.D., from the USDA Agricultural Research Service also received awards. Irish is spearheading research with a $1.5 million award to identify HLB susceptibility genes in citrus, which will assist in future breeding efforts. Simon received $1.5 million to lead efforts to develop a phloem-restricted viral vector that could be used to directly target CLas in the phloem or modulate citrus host responses. Shatters has received $9.4 million to explore the development of an in-field therapeutic screening system with accompanying delivery systems. Past-funded CRB researcher Goutam Gupta, Ph.D., was awarded $4.8 million to lead efforts in developing novel therapies for the prophylactic and curative treatment of HLB.

    Additionally, researchers from the University of Florida and the University of Maryland received awards to study CLas, ACP and HLB strategies.

    Click here for more information on project scope and activities can be found at. The CRB congratulates all awardees for the 2020 fiscal year cycle and looks forward to seeing the results from these studies.
     
    About the Citrus Research Board

    The CRB administers the California Citrus Research Program, the grower-funded and grower-directed program established in 1968 under the California Marketing Act as the mechanism enabling the state’s citrus producers to sponsor and support needed research. More information about the Citrus Research Board may be found at www.citrusresearch.org.

  • CDFA Accepting Proposals for Riverside County Grower Liaison

    The California Department of Food and Agriculture (CDFA) is currently accepting proposals for its Request for Proposal for a contractor to serve as the Riverside County grower liaison. Proposals must be received by Nov. 18. Responsibilities may include conducting outreach directly to growers in Riverside County, providing them up-to-date information on the latest industry news or updates, staying engaged in CDFA activities, communicating voluntary or mandatory treatments Riverside County and more.

    The battle to save California citrus from the Asian citrus psyllid (ACP) and Huanglongbing (HLB) is a collaborative effort that involves local, county, state and federal officials, researchers, scientists and commercial citrus growers. To help facilitate pest management and disease eradication, grower liaisons are key pieces to that puzzle and are dedicated to serving a specific region in the fight against HLB.

    This position requires a fundamental knowledge of citrus production, a working knowledge of grove operations, and the relationship between growers, shippers and allied businesses that work in the area of pest and disease control. A Pest Control Advisor’s license is desirable, but not required. The contractor should be familiar with California agriculture and specifically its citrus industry. Knowledge of the ACP and HLB is desirable.

    To submit a bid for the contract, you must follow these steps:

    • Visit ca.gov, if you do not have a profile you must register for one in order to view the Request for Proposal (RFP).
    • Once logged in, visit the Get Public Procurement Information page and select “See current bids.”
    • Under “Search Events,” type in “Asian Citrus Psyllid Outreach and Education.”
    • Once on the Events Details page, click “View Event Package,” then under the “View Attachments” area, click “view” to download the official Request for Proposal. Once there, you should be able to view the full RFP and Start a Bid if you meet the qualifications. Please note, you must have a profile and be logged in to view the RFP.

    Proposals are due to CDFA by Nov. 18 at 2 p.m. The term of this contract is Dec. 1, 2020 or upon final signature, whichever is later, through Nov. 30, 2022.

    For additional questions, contact Contracts Analyst Donna Weber at donna.weber@cdfa.ca.gov.

  • To all San Joaquin Valley Citrus Growers

    The ACP/HLB San Joaquin Valley Task Force called a meeting on October 8, 2020 due to the increased number of ACP trap finds in the southern part of Kern County. In the last month (September and into October), there

    have been a total of 35 ACP trap finds in the areas of the south part of Bakersfield, Arvin, Lamont, Mettler, and Maricopa. There were 15 residential and 20 commercial citrus sticky trap finds. While there have been finds in

    some of these areas in the past, the amount of detections in this last 30-day period is alarming. The Asian citrus psyllid, as a reminder, transmits Huanglongbing; the best way to avoid HLB is to control ACP which the valley has been successfully doing. 2020 has been a suspiciously quiet year for ACP finds but now, it is time to act.

    We are now in the late part of the season where most spray programs have already been executed. A coordinated spray is not recommended at this time. Kern County growers are encouraged to use an ACP effective material if they have not done so in the last six weeks. It is prudent for all growers to use ACP effective materials when treating other pests. Regarding the residential finds, CDFA is at various stages of treating them. Prior to these finds, CDFA had released Tamarixia radiata in certain residential areas of Kern County. Future Tamarixia releases are scheduled.

    The task force wants to convey the seriousness of what is being seen and what it means to our industry. Unfortunately, the suspicion is that these finds in commercial citrus are spilling over from residential properties. It is up to the citrus industry to deal with this threat. San Joaquin Valley citrus growers have done a good job using ACP effective materials when treating. The cooperation shown by growers during coordinated treatments reflects their commitment to keeping ACP suppressed. Nevertheless, task force members wished to highlight what should be done to help control the Asian citrus psyllid here in the valley.

    It is even more imperative to control the psyllid due to the find of a CLas positive ACP in commercial citrus down in the Riverside area. That was a wake-up call. We cannot, as an industry and in good conscience, dismiss that find. Growers and Pest Control Advisors need to be diligent. The following best practices must be a part of the regime tending to citrus groves.

    What do Growers and Pest Control Advisors need to do? It is easy to say, “follow the best practices”, but there are key elements that the task force believes is important. All the guidelines should be adhered to, but these are the key elements:

    A. Know When and Where Asian citrus psyllids might be present.
    – flush is what attracts the psyllid. Nice, tender leaves and stems. Like candy to an ACP.
    – citrus varieties matter. Lemons flush constantly. Grapefruit, oranges, and mandarins will have fewer flush cycles.
    – know when flushes occur. Spring, late summer for established trees. Younger trees have extensive, prolonged flush. Topping and hedging will produce flush. Spraying with kaolin stimulates flush also.

    – temperature determines how long a flush will last. Hot temps lead to quick hardening of the plant growth. Cooler temps prolong flush.

    1. Scout for Asian citrus psyllids (Yellow sticky traps are a passive method to determine presence of ACP).

      – use both visual and tap surveying.
      – survey along the borders, psyllids tend to not go deeper into groves unless the population is high (they do not like each other very much). If very wide plantings or very wide wind machine rows exist, then check along them too. Younger trees and shorter trees will allow the psyllids to travel farther into the grove.
      – do more frequent surveys during flush. Monthly surveys work when the vegetation is hardened off, unless the trees are close to a find, then sampling frequency should increase.

    2. Be aware of inadvertently transporting ACP.
      – clean equipment used before moving to the next property. Applies to anyone working in a grove; especially picking crews, trimming crews, irrigators, Pest Control Advisors, and the growers themselves.
      – check clothing and vehicles for insect hitchhikers. Shake out hats, bags, clothing. Sweep down vehicles.
      – do not park vehicles in the rows, park outside of the grove.

    3. If possible, use ACP effective materials when treating other pests, following label instructions.

    4. Follow the requirements when moving bulk harvested citrus.

    5. Be aware of developments!
      – receive newsletters from San Joaquin Valley Grower Liaisons.

    Fresno County Northern Tulare County Southern Tulare County Kern County

    – subscribe to industry publications.

    Sylvie Robillard Teri Blaser Jessica Leslie Judy Zaninovich

    FresnoACP@yahoo.com TBlaserSCI@ocsnet.net jess.leslie@hotmail.com jleslie@msn.com

    These were felt to be the most important points of the voluntary best practices. The ACP/HLB San Joaquin Valley Tack Force felt it was important to write this letter to all the valley citrus growers because as of this moment, the valley has not discovered a CLas positive Asian citrus psyllid or a CLas positive tree. The members of the task force believe that the industry must operate under the assumption that there are positive psyllids and trees in the valley; they just have not been found yet. If the industry relaxes its vigilance that is when Huanglongbing will become established and cause havoc. Thank you for taking the time to read this and may each and all stay safe and well.

    Sincerely,

    The ACP/HLB San Joaquin Valley Task Force 

  • HLB Detection Triggers Quarantine Expansion in San Bernardino & Los Angeles Counties

    A quarantine expansion has been declared following the detection of the citrus disease Huanglongbing (HLB), or citrus greening, in five residential citrus trees located in Rancho Cucamonga. This is the first time the disease has been confirmed in Ranch Cucamonga, marking the fifth city in San Bernardino County to have had a positive detection of HLB. The California Department of Food and Agriculture (CDFA) is working with the United States Department of Agriculture (USDA) and San Bernardino County to remove the HLB-infected tree and prevent the spread of HLB into neighboring areas.

    The expanded quarantine area will merge with the existing quarantines in San Bernardino and Los Angeles Counties. The expanded portion is bordered on the north by Big Tree Cucamonga; on the west by Pauda Avenue in Claremont and Mount Baldy Road; on the east by Interstate 15; and on the south by Foothill Boulevard and Interstate 10 in San Bernardino County.

    The updated HLB quarantine maps for San Bernardino and Los Angeles counties are available online. Please check this link for future quarantine expansions in these counties, should they occur.

    The quarantine prohibits the movement of all plant parts or citrus nursery stock out of the quarantine area. Provisions exist to allow the movement of commercially cleaned and packed citrus fruit. If you are a grower within the new quarantine expansion area, please contact CDFA’s emergency quarantine response program at 916-654-0312 for information on these provisions.

    Fruit that is not commercially cleaned and packed, including residential citrus, such as oranges, lemons, grapefruits and kumquats, must not be moved from the property on which it is grown, although it may be processed (removal of stems and leaves, and a thorough washing) and/or consumed on the premises.

    Residents are urged to take several steps to help protect citrus trees:

    • Do not move citrus plants, leaves, or foliage into or out of the quarantine area or across state or international borders. Keep it local.
    • Cooperate with agricultural officials placing traps, inspecting trees, and treating for the pest.
    • If you no longer wish to care for your citrus tree, consider removing it so it does not become a host to the pest and disease.

    CDFA staff have scheduled removal of the infected tree and are in the midst of a treatment program for citrus trees within 250-meters of the find site. By taking this action, a critical reservoir of the disease and its vectors will be removed, which is essential to protect other citrus trees on the property, neighbors’ trees and the community’s citrus from this deadly disease. CDFA, in partnership with USDA, local county agricultural commissioners and the citrus industry, continue to pursue a strategy of controlling the spread of the Asian citrus psyllids while researchers work to find a cure for HLB.

    Questions? If you are a citrus grower in San Bernardino County and have questions about this detection, please contact your grower liaison Sandra Zwaal at szwaal2@gmail.com.

  • New Targets for Huanglongbing Treatments

    Scientists are closer to gaining the upper hand on a disease that has wiped out citrus orchards across the globe. New models of the bacterium linked to the disease reveal control methods that were previously unavailable.

    Metabolic models of organisms are like road maps of cities. “They show you all the biological processes, and how they work together,” said UC Riverside microbiology professor James Borneman. “They also show you which molecular pathways, if blocked, will kill the organism.” 

    Simplified metabolic model and its striking similarity to a road map. (Metallo&Vander Heiden)

    In this case, researchers created the first models of the bacterium associated with Huanglongbing or HLB, also known as citrus greening disease. The team’s work is described in a new paper published in Nature’s npj Systems Biology and Applications.

    The research team made models for six different strains of the bacterium known as CLas and doing so enabled them to identify as many as 94 enzymes essential for the bacterium’s survival. These enzymes can now be considered targets for the creation of new antibacterial treatments.

    In addition, the team identified metabolites required for the bacteria to grow.

    “Just like when humans break down the food they eat into small components called metabolites, which feed our cells, bacterial cells also require metabolites for their growth,” Borneman said.

    Knowing the metabolites needed for CLas’ growth could enable scientists to cultivate it in a laboratory setting. It is not currently possible to grow CLas on its own, hindering scientists’ ability to study it and ultimately to manage it.

    This research project involved a collaboration between UC Riverside, UC San Diego, Texas A&M University, and the U.S. Department of Agriculture. In addition to Borneman, members of the modeling team included UCR plant pathologist Georgios Vidalakis and UCSD systems biologist Karsten Zengler.

    UC Riverside is at the forefront of efforts to combat Huanglongbing. Other important areas of research include antibacterial development and delivery, immune system fortification in citrus, engineering resistant citrus via a detailed understanding of host-microbe interactions, breeding resistant citrus, and insect management, among others.

    Because microbes tend to mutate and acquire resistance mechanisms in response to drugs and other efforts to thwart them, Borneman cautions that any one solution to the problem may be short-lived.

    Transmission electron microscope image of CLas bacterium. (J.M. Bové/INRA)

    “Microbes almost always adapt to control measures, perpetuating the ‘arms race’ between pathogens and hosts,” Borneman said. “There won’t be one thing that will fix this disease. We likely will need to address all three components associated with the disease — the bacterium, the insect that transmits it, and the citrus plants — to find a long-lasting solution.”

    To that end, the research team is constructing metabolic models of citrus and the insect, the Asian citrus psyllid.

    “We expect that this multiorganism modeling endeavor will provide new insights into the mechanisms underlying this disease, which will lead to effective and sustainable Huanglongbing management strategies,” Borneman said. — By Jules Bernstein, UC Riverside

  • Barking Up the Right Tree: Canines Detect HLB

    In September 2019, huanglongbing—also known as HLB or citrus greening—was detected in residential citrus trees located in Ventura County, in southern California (and just recently, the first HLB carrying Asian Citrus Psyllid was detected in a commercial CA citrus grove).

    During an orchard review in California, expert detector dog, Szaboles alerts his trainer by sitting next to a citrus tree infected with Huanglongbing (HLB).

    The disease, which has no known cure, is caused by a bacterium that devastates citrus plants and is transmitted by psyllids (small plant-eating insects resembling lice) that carry the bacteria from tree to tree or by the grafting of infected plant material. Common symptoms of infection include blotchy mottling of entire leaves, premature defoliation of the tree, and fruits that are usually small, with green peel at the bottom and a bitter taste. Unfortunately, these visible signs of HLB do not manifest until months or even years after the initial infection. By then, it is too late for citrus growers to save their crop from a mass infestation.

    However, the Farm Bureau of Ventura County found a rather unconventional way around this problem.

    To contain the infected trees and prevent a citrus epidemic, the Farm Bureau decided to hire a team of detector dogs specially trained to find HLB bacteria. The dogs are a result of a unique program funded by USDA and run by Agricultural Research Service (ARS) Research Leader and Plant Pathologist Timothy Gottwald (now retired) at the U.S. Horticultural Research Laboratoryin Fort Pierce, FL.

    First, the clever canines patrolled the perimeter because the edges of a grove are where the disease would first accumulate. Then, they trotted through the grove of trees to ultimately identify over 200 infected trees from a grove of 3,500.

    According to Gottwald’s research, the canine-detection method has an accuracy rate of 99 percent. While humans need several minutes to visually examine each tree and collect samples for laboratory testing (which requires considerable lab time and supplies), the dogs can travel through groves of trees in mere minutes, sensing HLB-infected trees by smell faster and far more easily. The time saved in finding the disease earlier gives citrus growers the opportunity to remove and destroy or quarantine HLB-infected trees, controlling what could’ve been a severe outbreak and loss of crop.
     

    However, there are still some considerations to keep in mind when deploying the canines as an early detection technology. Each dog team can only work 30 minutes at a time before they must rest, and a new team takes over. Teams can work for about 6 hours a day. In addition, much like any lab equipment, dogs are periodically calibrated to the HLB “scent signature” to remain finely honed optimized detectors.

    Still, the dogs are more sensitive and accurate than any other available technology in the field. The employment of detector dogs is still a voluntary program, which means fruit growers and farmers have the choice to either use dogs to find HLB early or continue using a USDA-approved DNA test called polymerase chain reaction (PCR).

    “While PCR is an effective way to detect infections, it isn’t efficient,” Gottwald explained. “It’s difficult to pinpoint incomplete infections—or infections that are only on one part of a plant (for example, a single leaf out of an entire tree with possibly thousands of leaves)—using PCR because it requires numerous samples from all over the suspect specimen.”

    “On the other hand,” Gottwald continued, “detector dogs identify pathogens ‘holistically,’ easily locating minute infections regardless of what small part of the tree they are infecting.” With this increased scope and accuracy rate, Gottwald and his colleagues believe that the canines’ abilities will revolutionize how growers protect their crops.

    “These specially trained canines may also be used to detect diseases and infections in other fruits and vegetables, such as grapes, peaches, plums, and tomatoes,” he said. “Our research has shown that they can sense pathogens like plum pox virus or squash vein yellowing virus, which both can cause severe economic losses to agriculture industries.”

    The canine-detection method was validated in blind tests by USDA ARS in collaboration with the California Department of Food and Agriculture, with results published in 2020.— By Georgia Jiang, USDA-ARS