- Author: Ben Faber
ITHACA, N.Y. — New clues to how the bacteria associated with citrus greening infect the only insect that carries them could lead to a way to block the microbes' spread from tree to tree, according to a study in Infection and Immunity by Agricultural Research Service (ARS) and Boyce Thompson Institute (BTI) scientists.
Citrus greening, also known as “huanglongbing,” is a serious disease dramatically affecting citrus production across the world. Trees with this disease all die after only a few years. Citrus greening has been detected in every citrus-producing county in Florida, throughout the southern citrus growing states and in isolated spots in southern California. There is no effective prevention or cure.
The disease is associated with the bacterium Candidatus Liberibacter asiaticus, CLas for short, which is spread from tree to tree only by a tiny insect vector—the Asian citrus psyllid. If CLas cannot infect the psyllid, its ability to spread citrus greening is halted.
With the long-term goal of disrupting this CLas-Asian citrus psyllid interaction, research molecular biologist and BTI professor Michelle Heck, with the ARS Emerging Pests and Pathogens Research Laboratory, and BTI researcher Marina Mann focused on an important point: not all psyllids spread CLas equally well.
To be spread by the Asian citrus psyllid (ACP) effectively, the bacteria must pass through the cells lining the insect's gut and multiply. Scientists in Heck's lab had previously shown that the gut cells of adult ACP show severe stress responses when infected by CLas. The cell nuclei become fragmented, and some cells react to the point of dying, allowing the bacteria to move out of the psyllid and into the tree.
Now, the researchers have found that, unlike adult psyllids, young psyllid nymphs appear to be resistant to the effects of exposure to CLas, and their nuclei rarely reach the same level of disruption. This means CLas cannot enter psyllid gut cells to multiply.
The next step will be to identify the mechanism for this resistance in the nymphs so that it might be manipulated to also halt the spread of CLas by the adults. An important clue lies in how psyllid nymphs interact with symbiotic bacteria in their gut, especially Wolbachia pipientis.
Many insects are hosts for Wolbachia and often depend on these bacteria for important benefits—much like how human health depends on gut bacteria. In their study, Mann and Heck showed that in psyllid nymphs, Wolbachia and CLas are commonly found within the same cells.
The authors hypothesize that, in accommodating the beneficial bacteria, the nymphs also let in more CLas. This is supported by their finding that CLas levels in psyllid nymphs are strongly correlated with Wolbachia levels. Though this link remains to be tested directly, understanding its mechanism could yield an important target for disrupting CLas-psyllid interaction.
“CLas exploits the way nymph and adult psyllids differ in their guts to gain entry into its insect vector,” Heck said. “We may be able to use this new foothold in our understanding to develop ways to block transmission by insects in the citrus grove.”
If this works, “citrus growers will be in a much better situation in terms of disease control and saving the U.S. citrus industry,” said Dan Dreyer, Chairman of the California Citrus Research Board, which funds this and other research aimed at developing a management strategy for citrus greening.
“There are still many unanswered questions about CLas, how it is acquired and transmitted via the Asian citrus psyllid, and how it causes the disease,” continued Dreyer. “The more we learn about CLas and its vector, the closer we will get to moving citrus production past the threat of citrus greening.”
The Agricultural Research Service is the U.S. Department of Agriculture's chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in agricultural research results in $20 of economic impact.
—USDA ARS
- Author: Ben Faber
HLB Confirmations The number of trees confirmed as being infected by HLB has reached 520 (300 in Orange County, 217 in Los Angeles County and 3 in Riverside County). All were in residential settings, not commercial groves. The HLB quarantine boundaries and the latest tally of HLB confirmations, updated weekly, is available online at https://citrusinsider.org/maps/. As confirmations increase and spread closer to commercial citrus, it is a good time to consider removing citrus trees not worth the resources required to protect them from ACP and HLB. ACP Areawide Treatments The winter ACP areawide treatment window ended March 16. Please remember to submit your Pesticide Use Reports (PURs) to the County Ag Commissioner's office immediately after treatment to ensure your ACP treatment is recognized. ACP treatment percentages will be calculated in about a month, to allow time for all PURs to be filed. The spring-summer uncoordinated ACP treatment window begins now and continues through July. Although these treatments are not coordinated, psyllid populations need to be kept low to reduce the risk of HLB. Scout/monitor and treat if you see any ACP, and use an ACP-effective material during spring/summer management. Click here to access the University of California recommendations for ACP monitoring. Save the Date The fall 2018 areawide-treatment protocols and schedule will be discussed at a grower workshop on Thursday, April 26, at the Agriculture Museum in Santa Paula. Additional details will be distributed soon. Meetings The Citrus Pest & Disease Prevention Program will conduct a free crew boss training from 7 to 9 a.m. on March 28 at the Limoneira Visitor Center, 1141 Cummings Road, Santa Paula. Growers and packers are encouraged to send crew bosses, foremen, ranch managers and packinghouse representatives to this hands-on learning experience. Presented in Spanish, these trainings will inform front-line leaders in the field about what they can do to reduce the risk of spreading HLB and ACP at work. Click here for more information and to register. The Citrus Pest and Disease Prevention Committee will meet in Ventura County on Wednesday, May 9. Attendance is free. The CDFA site with agenda, venue, and webinar information is at https://www.cdfa.ca.gov/citruscommittee/. On a related note, the CPDPC recently approved the appointment of Ted Grether of Somis to represent coastal citrus growers on the committee. Ted works for the family farming business, Grether Farming Company, growing lemons, avocados and mandarins as an operations manager and administrator. Resources Please direct questions about regulatory or compliance agreement issues to the County Agricultural Commissioner's Office (David Navarro, david.navarro@ventura.org, 805-388-4343) or CDFA (Michael Soltero, Michael.Soltero@cdfa.ca.gov, 805-445-1382). Click here to sign up for the Ventura County ACP-HLB Task Force mailing list. If you need pest control or tree removal referrals, please contact your grower liaisons, Sandra Zwaal and Cressida Silvers. Low- or no-cost tree removal assistance can also be obtained through California Citrus Mutual's ACT NOW program. More information can be found at https://citrusmatters.cropscience.bayer.us/commercial-grower/act-program.
Cressida Silvers (805) 284-3310
Sandra Zwaal (949) 636-7089 |
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- Author: Ben Faber
In the citrus world there is a relative tolerance to the bacteria that causes Huanglongbing, or Citrus Greening. Grapefruit and some orange varieties are very sensitive and some mandarin varieties are much more tolerant, meaning they live longer in the presence of the bacteria. Work is being done to use mandarin juice as a substitute for the traditional glass of orange juice. A recent bulletin out from the University of Florida has this news. This does not mean that Asian Citrus Psyllid and Huanglongbing are any less of a threat to citrus at this point. Just a way of prolonging an industry until true solutions can be found.
GAINESVILLE, Fla. — Some people like to wake up and drink a glass of fresh Florida orange juice. With the greening disease ravaging Florida's citrus industry, University of Florida Institute of Food and Agricultural Sciences researchers want to make orange juice from disease-tolerant fruit.
Huanglongbing (HLB), or citrus greening as it's commonly called, has destroyed 80 percent of citrus in Florida, a state where citrus is an $8.6 billion-a-year industry, according to UF/IFAS research. About 90 percent of the state's oranges are used to make orange juice, UF/IFAS researchers say.
So it's critical that scientists find sources for orange juice upon which consumers can rely. UF/IFAS researchers have found some mandarins that are tolerant to citrus greening.
In a newly published study, UF/IFAS researchers also found that consumers sense little, if any difference in the smell and taste of certain specific mandarins, compared to oranges.
“We found out what makes orange taste like orange and mandarin taste like mandarin, even though they are very close species,” said Yu Wang, a UF/IFAS assistant professor of food science and human nutrition and lead author of the study.
“If we use greening-tolerant mandarin for orange-juice making, the first thing we need to know is the difference between them,” Wang said. “This will provide more possibilities and flexibilities for the citrus industry in particular in the HLB era.”
In the past, researchers used traditional methods such as gas chromatography-mass spectrometry to study the flavor differences in orange and mandarin, Wang said. But people's senses of taste and smell are much more sensitive than analytical equipment, so scientists integrated sniffing into the study, she said.
It's important to remember that oranges are descendants of mandarin and pummelos, said Fred Gmitter, a UF/IFAS horticultural sciences professor and co-author of the study. So there's already a lot of mandarin's genetic makeup in an orange.
The problem is that oranges are very sensitive to citrus greening, Gmitter said.
“While we find other selections in the breeding program, mostly mandarin, hold of up a lot better against greening, we are finding some of these selections produce fruit that more closely resemble orange in appearance,” Gmitter said. “But more importantly, here, that they also very closely resemble orange in flavor.”
The study is published in the Journal of Agricultural and Food Chemistry:
https://pubs.acs.org/doi/abs/10.1021/acs.jafc.7b04968?src=recsys
Brad Buck
UF|IFAS
- Author: Ben Faber
HLB confirmations The number of trees in Southern California confirmed to be infected with HLB has risen to 347, distributed across 16 communities in four counties. So far, all are in residential plantings, not in commercial groves. As HLB detections increase and spread closer to commercial citrus, it is a good time to consider removing citrus trees that are uncared for or not worth the resources required to protect them from ACP and HLB. The distribution of HLB confirmations, updated weekly, can be found on https://citrusinsider.org/maps/. Winter ACP area-wide cycle As a reminder, due to the Thomas Fire the treatment window for psyllid management areas in West Ventura and the Ojai Valley (PMAs 44-50) was delayed until Feb. 23-March 16. If you wish to confirm your treatment window or interim treatment percentages, or obtain referrals for pest-control or tree-removal services, please contact your grower liaisons, Sandra Zwaal and Cressida Silvers. Low- or no-cost tree removal assistance can also be obtained through California Citrus Mutual's Citrus Matters ACT NOW program. More information can be found at https://citrusmatters.cropscience.bayer.us/commercial-grower/act-program. HLB in the news ABC7 news and The San Bernardino Sun recently picked up a story regarding a San Bernardino County nursery caught up in the HLB quarantine, which led to destruction of its inventory of citrus trees. ABC News7 article with clip: http://abc7.com/food/ie-nurserys-citrus-trees-to-be-destroyed-by-ca-agriculture-department/2959173/ The Sun article: https://www.sbsun.com/2018/01/19/more-than-4000-citrus-trees-destroyed-while-disagreement-between-bloomington-nurseries-state-continues/ Meetings UC Riverside & Citrus Research Board Citrus Day for the Industry will be on Tuesday, Feb. 6, at UC Riverside. The deadline to register is Jan. 30. Registration is $35 and includes lunch. Online registration is available at https://form.jotform.com/80016278039152. Click here to download the program. The Citrus Pest and Disease Prevention Committee's operations and outreach subcommittees will meet Wednesday, Feb. 7, at the Mission Inn Hotel in Riverside. Attendance is free. The CDFA website with agenda, venue, and webinar information is at https://www.cdfa.ca.gov/citruscommittee/. If you have any questions, please contact one of the grower liaisons: Cressida Silvers (805) 284-3310 Sandra Zwaal (949) 636-7089 |
- Author: Kathy Keatley Garvey
The Asian citrus psyllid, the most devastating threat to the worldwide citrus industry, may have met its match.
In a ground-breaking discovery encompassing six years of research, an international team of scientists led by UC Davis chemical ecologist Walter Leal announced they've identified the sex pheromone of the pest, which feeds on citrus and transmits the bacteria that causes the deadly citrus greening disease known as Huanglongbing (HLB).
Leal, a native of Brazil and a fellow of both the Entomological Society of America and the Entomological Society of Brazil, revealed the discovery during his presentation Dec. 5 at the 10th Annual Brazilian Meeting of Chemical Ecology in Sao Paulo. His team included scientists from UC Davis, University of Sao Paulo, and the Fund for Citrus Protection (FUNDECITRUS) from the state of Sao Paulo.
“Dr. Leal's discovery of the Asian citrus psyllid pheromone is a significant breakthrough in preventing the spread of this serious citrus insect, and may offer a less toxic method for its control,” said integrated pest management specialist Frank Zalom, distinguished professor with the UC Davis Department of Entomology and Nematology and a past president of the Entomological Society of America. He was not involved in the study.
“Having a lure to dramatically improve captures of this psyllid with the conventional sticky traps is a major progress toward integrated pest management,” said Professor Jose Robert Parra of the University of Sao Paulo.
Identifying the sex pheromone proved “complicated and quite a challenge” because of the insect's complex behavior and biology, said Leal, a UC Davis distinguished professor who has discovered the sex pheromones of moths, beetles, bugs, cockroaches, mites and other arthropods. A patent was filed Friday, Dec. 1, and journal publication is pending.
Citrus trees infected with HLB usually die within five years, according to the UC Statewide Integrated Pest Management Program. There is no known cure. “The only way to protect trees is to prevent spread of the HLB pathogen in the first place, by controlling psyllid populations and removing and destroying any infected trees,” UC IPM says on its website.
Native to Asia, the Asian citrus psyllid, Diaphorina ciri, was first detected in the United States in June 1998 in Palm Beach County, Florida, and in California in August 2008 in San Diego County. Scientists discovered HLB in Florida in August 2005, and in Los Angeles in March 2012. The mottled brown insect, about 3 to 4 millimeters long, or about the size of an aphid, is now widespread throughout Southern California and is now found in 26 of the state's 58 counties.
The Asian citrus psyllid, or ACP, feeds on new leaf growth of oranges, lemons, mandarins, grapefruit and other citrus, as well as some related plants. Infected psyllids can transmit the bacterium Candidatus Liberibacter asiaticus, which causes the fatal citrus disease. An early symptom of HLB in citrus is the yellowing of leaves on an individual limb or in a sector of a tree's canopy.
Currently growers are using yellow sticky traps to detect the insect and to monitor the population. “Efficient lures,” Leal said, “are sorely needed for sticky traps, particularly for early ACP detection. Otherwise, growers have to resort to regular sprays to avoid infection given that infected insects from gardens and noncommercial areas migrate to citrus farms.”
Pheromones and other semiochemicals are widely used in agriculture and medical entomology. “Growers use them as lures in trapping systems for monitoring and surveillance, as well as for strategies for controlling populations, such as mating disruption and attraction-and-kill systems,” Leal noted.
Although ACP is present in Arizona and California, the disease itself has not been established, Leal said. “The emphasis is on detection, eradication and limiting the spread of the disease. In Florida, where HLB is widespread, monitoring ACP populations is essential to avoid reinfection after eradication of infected plants.”
The detection of the pest has led to widespread eradication of citrus trees in China, Brazil and the United States. “In Brazil as many as 46.2 million citrus trees, representing 26 percent of the currently planted trees, have been eradicated since the detection of HLB in 2004,” Leal said. “In Florida, HLB has caused severe losses to the citrus industry. This year's production loss is estimated to be about 28 million fewer boxes of oranges than in 2014-2015.”
The announcement of the discovery coincides with the 40th anniversary celebration of FUNDECITRUS in Araraquara, Sao Paolo. “I am delighted that Walter Leal accepted our challenge to work on this project as the lead investigator,” said Juliano Ayres, FUNDECITRUS director. “The combination of his work ethics and qualifications are unparalleled. And, he loves challenges.”
In response to the ACP invasion in California, the California Department of Food and Agriculture (CDFA) has launched an extensive monitoring program to track the distribution of the insect and disease. They check yellow sticky traps in both residential areas and commercial citrus groves, and also test psyllids and leaf samples for the presence of the pathogen.
Survey methods for ACP include visual inspections, sweep netting, and placement of yellow sticky traps in trees in citrus nurseries, commercial citrus-producing areas and residential properties throughout the state, according to the CDFA. They also place sticky traps in California fruit packing houses, specialty markets, retail stores and airports that receive such produce from areas known to be infested with ACP.
Since August 2008, ACP has now been detected in 26 of California's 58 counties: Alameda, Contra Costa, Fresno, Imperial, Kern, Kings, Los Angeles, Madera, Merced, Monterey, Orange, Placer, Riverside, San Benito, San Bernardino, San Diego, San Joaquin, San Luis Obispo, San Mateo, Santa Barbara, Santa Clara, Solano, Stanislaus, Tulare, Ventura, and Yolo. “The ACP has the potential to establish itself throughout California wherever citrus is grown,” the CDFA says on its website.
CDFA has set up a hotline at 1-800-491-1899 for residents to report suspicious insects or disease symptoms in their citrus trees.
Resources:
UC IPM|
http://ipm.ucanr.edu/PMG/r107304411.html
California Department of Food and Agriculture (CDFA)
https://www.cdfa.ca.gov/plant/PDEP/target_pest_disease_profiles/ACP_PestProfile.html
Save Our Citrus: Hotline Information
UC Agriculture and Natural Resources (UC ANR)
http://anrcatalog.ucanr.edu/pdf/8205.pdf