Citrus greening disease explained

Citrus greening disease
Common Names:HLB, citrus vein phloem degeneration (CVPD), citrus greening disease, yellow shoot disease, yellow dragon disease, leaf mottle yellows in the Philippines, citrus dieback in India
Causal Agents:Liberibacter spp. (L. asiaticus, L. africanus, L. americanus)[1]
Hosts:citrus trees
Vectors:Diaphorina citri, Trioza erytreae
Eppo Codes:1LIBEG
Distribution:Asia, Africa, United States

Citrus greening disease[2] (abbr. HLB)[3] is a disease of citrus caused by a vector-transmitted pathogen. The causative agents are motile bacteria, Liberibacter spp. The disease is transmitted by the Asian citrus psyllid, Diaphorina citri, and the African citrus psyllid, Trioza erytreae. It has no known cure.[4] It is graft-transmissible.[5]

There are three different types of the disease: a heat-tolerant Asian form, and the heat-sensitive African and American forms. It was first described in 1929, and first reported in South China[1] in 1943. The African variation was first reported in 1947 in South Africa, where it is still widespread. It reached Florida in 2005, and within three years had spread to the majority of citrus farms. The rapid increase in this disease has threatened the citrus industry in the entire US. As of 2009, 33 countries had reported the infection in their citrus crop.[6]

Symptoms

Citrus greening is distinguished by the common symptoms of yellowing of the veins and adjacent tissues (hence the "yellow dragon" name given by observing Chaozhou farmers as early as the 1870s[1]); followed by splotchy mottling of the entire leaf, premature defoliation, dieback of twigs, decay of feeder rootlets and lateral roots, and decline in vigor, ultimately followed by the death of the entire plant.[7] Affected trees have stunted growth, bear multiple off-season flowers (most of which fall off), and produce small, irregularly shaped fruit with a thick, pale peel that remains green at the bottom and tastes very bitter. Common symptoms can be mistaken for nutrient deficiencies; the distinguishing factor is the pattern of symmetry. Nutrient deficiencies tend to be symmetrical along the leaf vein margin, while HLB has an asymmetrical yellowing around the vein. The most noticeable symptom of HLB is greening and stunting of the fruit, especially after ripening.[8]

Transmission

Citrus greening was originally thought to be a viral disease, but is caused by a bacterium, carried by insect vectors. Infection can arise in various climates and is often associated with different species of psyllid insects.[9] For example, citrus crops in Africa become infected under cool conditions as the bacteria are transmitted by the African citrus psyllid Trioza erytreae,[10] an invasive insect that favors cool and moist conditions for optimal activity. Citrus crops in Asia, however, are often infected under warm conditions as the bacteria are transmitted by the Asian citrus psyllid Diaphorina citri.[11] [12]

The young larval stage is the most suitable for acquisition of ca. L. asiaticus by the Asian citrus psyllid Diaphorina citri,[12] and some cultivars show greater efficiency in transmitting the disease to the vector than others.[13] Temperature also shows a great influence in the parasite-host relationship between the bacteria and the insect vector, affecting how it is acquired and transmitted by the insects.[13]

The causative agents are fastidious phloem-restricted, Gram-negative bacteria in the gracilicutes clade. The Asian form, ca. L. asiaticus is heat tolerant. This means the greening symptoms can develop at temperatures up to 35 °C. The African form, ca. L. africanus, and American form, ca. L. americanus, are heat sensitive, thus symptoms only develop when the temperature is in the range 20–25 °C.[14] Although T. erytreae is the natural vector of African citrus greening and D. citri is the natural vector of American and Asian citrus greening, either psyllid can in fact transmit either of the greening agents under experimental conditions.[15]

Distribution

Distribution of the Asian citrus psyllid is primarily in tropical and subtropical Asia. It has been reported in all citrus-growing regions in Asia except mainland Japan. The disease has affected crops in China, India, Sri Lanka, Malaysia, Indonesia, Myanmar, the Philippines, Pakistan, Thailand, the Ryukyu Islands, Nepal, Saudi Arabia, and Afghanistan. Areas outside Asia have also reported the disease: Réunion, Mauritius, Brazil, Paraguay, and Florida since 2005, and in several municipalities in Mexico since 2009[16] [17] [18] [19] [20] On March 30, 2012, citrus greening disease was confirmed in a single citrus tree in California.[21] The first report of HLB in Texas occurred on January 13, 2012, from a Valencia sweet orange tree in a commercial orchard in Texas.[22] Prospects are bleak for the ubiquitous backyard citrus orchards of California as residential growers are unlikely to consistently use the pesticides which provide effective control in commercial orchards.[23]

The distribution of the African citrus psyllid includes Africa, Madeira, Saudi Arabia, Portugal, and Yemen.[24] This species is sensitive to high temperatures and will not develop at temperatures greater than 25 °C. It is a vector of the African strain of huanglongbing (Candidatus Liberibacter africanus), which is sensitive to heat. This strain is reported to occur in Africa, (Burundi, Cameroon, Central African Republic, Comoros, Ethiopia, Kenya, Madagascar, Malawi, Mauritius, Reunion, Rwanda, South Africa, St. Helena (unconfirmed), Swaziland, Tanzania, Zimbabwe), Saudi Arabia, and Yemen. The disease was not reported in the EU as of 2004.[25]

Control

Some cultural practices are effective in managing this disease. Cultural methods include antibacterial management, sanitation, removal of infected plants, frequent scouting, and most importantly, crisis declaration.[26] Tracking the disease can help prevent further infection in other affected areas and help mitigate more local infections, if detected early enough. The Asian citrus psyllid has alternative hosts that may attract psyllids to citrus plants in the vicinity such as Murraya paniculata, Severinia buxifolia, and other plants in the family Rutaceae.[27]

No cure for citrus greening disease is known, and efforts to control it have been slow because infected citrus plants are difficult to maintain, regenerate, and study. Ongoing challenges associated with mitigating disease at the field-scale include seasonality of the phytopathogen (Liberibacter spp.) and associated disease symptoms, limitations for therapeutics to contact the phytopathogen in planta, adverse impacts of broad-spectrum treatments on plant-beneficial microbiota, and potential implications on public and ecosystem health.[28] The effort to culture Candidatus Liberibacter asiaticus (CLas) has been a significant challenge in plant pathology. Progress has included culturing a different species of Liberibacter.[29]

No naturally immune citrus cultivars have been identified; however, creating genetically modified citrus may be a possible solution, but questions of its acceptability to consumers exist.[30] A researcher at Texas AgriLife Research reported in 2012 that incorporating two genes from spinach into citrus trees improved resistance to citrus greening disease in greenhouse trials.[31] Field tests by Southern Gardens Citrus of oranges with the spinach genes in Florida are ongoing.[30]

A resistant variety of mandarin orange called 'Bingo' has been bred at the University of Florida.[32] Some other varieties have a partial tolerance to the disease.[33]

Antibiotics

Researchers at the Agricultural Research Service of the United States Department of Agriculture have used lemon trees infected with citrus greening disease to infect periwinkle plants to study the disease. Periwinkle plants are easily infected and respond well when experimentally treated with antibiotics. Researchers are testing the effect of penicillin G sodium and biocide 2,2-dibromo-3-nitrilopropionamide as potential treatments for infected citrus plants based on the positive results that were observed when applied to infected periwinkle.[34] In June 2014, the USDA allocated an additional US$31.5 million to expand research combating the disease.[35]

Certain antibiotics, specifically streptomycin and oxytetracycline, may be effective and have been used in the United States, but are banned in Brazil and the European Union.[36] In 2016, the EPA allowed use of streptomycin and oxytetracycline on orchards with citrus fruits like grapefruits, oranges and tangerines in Florida on an emergency basis, this approval was expanded and broadened to other states for oxytetracycline in December 2018.[36] Further expansion of medically important antibiotics is proposed by the EPA but opposed by the FDA and CDC, primarily as antibiotic resistance can be expected to develop and affect human health.[36] [37]

Possible future treatments

A peptide that prevents and treats citrus greening disease in greenhouse trials was being tested in field trials in 2021;[38] [39] an enhanced injectable version of the product was being developed in 2020.[40]

Two types of antisense oligonucleotide (FANA and Morpholinos) can be delivered efficiently into citrus trees,[41] suppressing their RNA targets. FANA can suppress 'Candidatus Liberibacter asiaticus' in citrus trees.[42] [43]

Morpholinos can suppress CLas in infected citrus trees and the psyllid vectors. Furthermore, the PPMOs designed to endosymbiotic bacteria of the psyllid vectors, can reduce psyllid populations by targeting and suppressing the insects endosymbionts, the bacteria which are essential for psyllid survival.[44] [45] Morpholinos must be covalently linked with a charged molecule or peptide, to enter bacteria. The target RNA is made susceptible to cleavage by ribonuclease P (RNase-P).[46]

Cover crops

Some success has been reported using a cover crop strategy.[47] The citrus trees were not free of the disease bacteria, yet a healthy soil environment allowed them to produce fruit and remain profitable.[48] [49]

See also

Further reading

External links

Notes and References

  1. Bové . J.M. . Huanglongbing: a destructive, newly-emerging, century-old disease of citrus . Journal of Plant Pathology . March 2006 . 88 . 1 . 7–37 . 41998278 .
  2. Web site: Citrus greening . Animal and Plant Health Inspection Service . 21 September 2023.
  3. Web site: The Disease: Huanglongbing (HLB) . Citrus Research Board . 29 November 2010 . 17 January 2011 . https://web.archive.org/web/20110117005300/http://www.californiacitrusthreat.org/huanglongbing-citrus-greening.php . dead.
  4. Killiny . Nabil . Nehela . Yasser . George . Justin . Rashidi . Mahnaz . Stelinski . Lukasz L. . Lapointe . Stephen L. . 2021-07-01 . Phytoene desaturase-silenced citrus as a trap crop with multiple cues to attract Diaphorina citri, the vector of Huanglongbing . Plant Science . 308 . 110930 . 10.1016/j.plantsci.2021.110930 . 34034878 . 235203508 . free . 2021PlnSc.30810930K .
  5. Lin . K. H. . 1956 . Observation on yellow shoot on citrus. Etiological studies of yellow shoot on Citrus . Acta Phytopathological Sinica . 2 . 1–42.
  6. Web site: Voosen . P. . National Geographic . Can Genetic Engineering Save the Florida Orange? . https://web.archive.org/web/20140915182959/http://news.nationalgeographic.com/news/2014/09/140914-florida-orange-citrus-greening-gmo-environment-science/ . dead . September 15, 2014 . 13 September 2014 . 17 June 2017.
  7. Li . Xue . Ruan . Huaqin . Zhou . Chengqian . Meng . Xiangchun . Chen . Wenli . 2021 . Controlling Citrus Huanglongbing: Green Sustainable Development Route Is the Future . Frontiers in Plant Science . 12 . 10.3389/fpls.2021.760481 . 8636133 . 34868155 . free .
  8. Web site: UF/IFAS Citrus Extension: Plant Pathology . Crec.ifas.ufl.edu . 17 June 2017 . 14 April 2021 . https://web.archive.org/web/20210414024850/https://crec.ifas.ufl.edu/extension/greening/symptoms.shtml . dead.
  9. Gutierrez . Andrew Paul . Ponti . Luigi . 2013 . Prospective Analysis of the Geographic Distribution and Relative Abundance of Asian Citrus Psyllid (Hemiptera:Liviidae) and Citrus Greening Disease in North America and the Mediterranean Basin . Florida Entomologist . 96 . 4 . 1375–1391.
  10. Web site: Arengo . E . Trioza erytreae (African citrus psyllid) . CABI Digital Library . Centre for Agriculture and Bioscience International (CABI) . 17 June 2017.
  11. Web site: CISR: Asian Citrus Psyllid . Center for Invasive Species Research . University of California Riverside . 17 June 2017.
  12. Wu. Fengnian. Qureshi . Jawwad A . Huang . Jiaquan . Fox . Eduardo Gonçalves Paterson . Deng . Xiaoling . Wan . Fanghao . Liang . Guangwen . Cen . Yijing . 2018-07-12 . Host Plant-Mediated Interactions Between 'candidatus Liberibacter asiaticus' and Its Vector Diaphorina citri Kuwayama (Hemiptera: Liviidae) . Journal of Economic Entomology . 111 . 5 . 2038–2045 . 10.1093/jee/toy182 . 30010958 . 51628267.
  13. Wu . Fengnian . Huang . Jiaquan . Xu . Meirong . Fox . Eduardo G P . Beattie . G Andrew C . Holford . Paul . Cen . Yijing . Deng . Xiaoling . 5 . December 2018 . Host and environmental factors influencing 'candidatus Liberibacter asiaticus' acquisition in Diaphorina citri: Interactions between D. citri and 'candidatus Liberibacter asiaticus'. Pest Management Science . 74 . 12 . 2738–2746 . 10.1002/ps.5060 . 29726075 . 19098533.
  14. Garnier . M. . S. . Jagoueix-Eveillard . P. R. . Cronje . G. F. . LeRoux . J. M. . Bové . 2000 . Genomic characterization of a Liberibacter present in an ornamental rutaceous tree, Calodendrum capense, in the Western Cape Province of South Africa. Proposal of 'candidatus Liberibacter africanus subsp. capensis . International Journal of Systematic and Evolutionary Microbiology . 50 . 2119–2125.
  15. Lallemand . J. . A. . Fos . J. M. . Bové . 1986 . Transmission de la bacterie associé à la forme africaine de la maladie du 'greening' par le psylle asiatique Diaphorina citri Kuwayama . French . Fruits . 41 . 341–343.
  16. Web site: Detection of Huanglongbing (Candidatus Liberibacter asiaticus) in the municipality of Tizimin, Yucatan, Mexico . North American Plant Protection Organization's Phytosanitary Alert System . 2010-10-02.
  17. Web site: Update on the detection of Huanglongbing (Candidatus Liberibacter asiaticus) in backyard trees in the States of Yucatan and Quintana Roo, Mexico. North American Plant Protection Organization's Phytosanitary Alert System. 2010-10-02.
  18. Web site: Update on the detection of Huanglongbing (Candidatus Liberibacter asiaticus) in backyard trees in Mexico. North American Plant Protection Organization's Phytosanitary Alert System. 2010-10-02.
  19. Web site: Detection of Huanglongbing (Candidatus Liberibacter asiaticus) in the Municipality of Calakmul, Campeche, Mexico . North American Plant Protection Organization's Phytosanitary Alert System . 2010-10-02.
  20. Web site: Detection of Huanglongbing (Candidatus Liberibacter asiaticus) in the Municipalities of Mazatlan and Escuinapa, Sinaloa, Mexico. North American Plant Protection Organization's Phytosanitary Alert System. 2010-10-02.
  21. Web site: Citrus Disease Huanglongbing Detected in Hacienda Heights Area of Los Angeles County . California Department of Food and Agriculture . April 18, 2012 . Press release . March 30, 2012.
  22. Kunta . M. . Sétamou . M. . Skaria . M. . Rascoe . J. . Li . W. . Nakhla . M. . da Graça . J.V. . 2012 . First report of citrus Huanglongbing in Texas . Phytopathology . 102 . S4.66.
  23. News: Ian . Lovett . April 17, 2012 . Threat to California Citrus May Finish Backyard Trees . April 18, 2012 . The New York Times.
  24. Web site: European and Mediterranean Plant Protection Organization/Centre for Agricultural Bioscience International . 1979 . EPPO data sheet on quarantine organisms, No. 46, Trioza erytreae . 17 June 2017 . dead . https://web.archive.org/web/20100713203449/http://www.eppo.org/QUARANTINE/insects/Trioza_erytreae/TRIZER_ds.pdf . 13 July 2010.
  25. Citrus greening bacterium . Data Sheets on Quarantine Pests . March 6, 2022 . March 9, 2016 . https://web.archive.org/web/20160309230852/http://www.eppo.int/QUARANTINE/data_sheets/bacteria/LIBESP_ds.pdf . dead.
  26. Web site: UF/IFAS Citrus Extension: Plant Pathology. Crec.ifas.ufl.edu. 17 June 2017. 13 April 2021. https://web.archive.org/web/20210413202540/https://crec.ifas.ufl.edu/extension/greening/management.shtml. dead.
  27. Web site: UF/IFAS Citrus Extension: Plant Pathology . Crec.ifas.ufl.edu . 17 June 2017 . 2 December 2020 . https://web.archive.org/web/20201202132434/https://crec.ifas.ufl.edu/extension/greening/hosts.shtml . dead.
  28. Blaustein. Ryan A.. Lorca . Graciela L. . Teplitski. Max . 2018-01-24. Challenges for Managing Candidatus Liberibacter spp. (Huanglongbing Disease Pathogen): Current Control Measures and Future Directions. Phytopathology . 108. 4. 424–435 . 10.1094/phyto-07-17-0260-rvw. 28990481. free.
  29. Merfa . M. V. . etal . 2019 . Progress and obstacles in culturing 'Candidatus Liberibacter asiaticus', the bacterium associated with Huanglongbing . Phytopathology . 109 . 7 . 1092-1101 .
  30. News: A Race to Save the Orange by Altering Its DNA . July 28, 2013. The New York Times. July 27, 2013. Amy . Harmon.
  31. Web site: Santaana R . 26 March 2012 . Spinach genes may stop deadly citrus disease . https://web.archive.org/web/20120416070022/http://today.agrilife.org/2012/03/26/transgenic-citrus-trees/ . 16 April 2012 . Agrilife Today . Texas A&M . 1 October 2012 .
  32. News: Allen . Greg . After A Sour Decade, Florida Citrus May Be Near A Comeback . 10 February 2017 . NPR . 4 December 2016.
  33. Web site: Promising new citrus varieties for greening tolerance . ScienceDaily . 5 December 2019.
  34. Web site: Dennis O'Brien . 2010-04-26 . Periwinkle Plants Provide Ammunition in the War on Citrus Greening . 2014-05-18 . USDA Agricultural Research Service.
  35. News: $31.5mn allocated by USDA for research to fight citrus fruit disease . canadianbusiness.com . 12 June 2014 . 4 July 2015 . https://web.archive.org/web/20150704195412/http://www.canadianbusiness.com/business-news/31-5-million-in-federal-funds-allocated-for-fight-against-citrus-greening/ . dead .
  36. News: Citrus Farmers Facing Deadly Bacteria Turn to Antibiotics, Alarming Health Officials . Andrew Jacobs. . May 17, 2019 . June 5, 2019.
  37. Web site: Antibiotic Use on Oranges Gets Trump Administration's Approval. Center for Biological Diversity. December 10, 2018. June 6, 2019.
  38. Huang . Chien-Yu . Araujo . Karla . Sánchez . Jonatan Niño . Kund . Gregory . Trumble . John . Roper . Caroline . Godfrey . Kristine Elvin . Jin . Hailing . 5 . 2021-02-09 . A stable antimicrobial peptide with dual functions of treating and preventing citrus Huanglongbing . Proceedings of the National Academy of Sciences . 118 . 6 . e2019628118 . 10.1073/pnas.2019628118 . 33526689 . 8017978 . 2021PNAS..11819628H . free.
  39. Wang . Nian . 2021-02-09 . A promising plant defense peptide against citrus Huanglongbing disease . Proceedings of the National Academy of Sciences . 118 . 6 . e2026483118 . 10.1073/pnas.2026483118 . 33526706 . 8017718 . 2021PNAS..11826483W . free .
  40. Web site: Bernstein . Jules . UC Riverside discovers first effective treatment for citrus-destroying disease . . July 7, 2020.
  41. Hunter . Wayne . 2017 . FANA and Morpholino's, Novel Molecules for Gene-Targeting in Plants and Arthropods . Proceedings of the XXV International Plant & Animal Genome Conference, January 14-18, San Diego, California . 25 . Paper25794.
  42. Hunter . Wayne Brian . Cooper . William Rodney . Sandoval-Mojica . Andres F. . McCollum . Greg . Aishwarya . Veenu . Pelz-Stelinski . Kirsten S. . 2021-07-08 . Improving Suppression of Hemipteran Vectors and Bacterial Pathogens of Citrus and Solanaceous Plants: Advances in Antisense Oligonucleotides (FANA) . Frontiers in Agronomy . 3 . 10.3389/fagro.2021.675247 . free.
  43. Sandoval-Mojica . Andrés F. . Hunter . Wayne B. . Aishwarya . Veenu . Bonilla . Sylvia . Pelz-Stelinski . Kirsten S. . 2021-02-02 . Antibacterial FANA oligonucleotides as a novel approach for managing the Huanglongbing pathosystem . Scientific Reports . 11 . 1 . 2760 . 10.1038/s41598-021-82425-8 . 7854585 . 33531619 . 2021NatSR..11.2760S .
  44. Book: Hunter . Wayne B. . Chapter Six - Emerging RNA Suppression Technologies to Protect Citrus Trees From Citrus Greening Disease Bacteria . 2018 . Smagghe . Guy . Crop Protection . Advances in Insect Physiology . 55 . 163–197 . https://doi.org/10.1016/bs.aiip.2018.08.001 . 2024-05-17 . Elsevier . 10.1016/bs.aiip.2018.08.001 . 978-0-12-815079-5 . Sinisterra-Hunter . Xiomara H. .
  45. Sandoval-Mojica . Andrés F. . Altman . Sidney . Hunter . Wayne B. . Pelz-Stelinski . Kirsten S. . 2020 . Peptide conjugated morpholinos for management of the huanglongbing pathosystem . Pest Management Science . 76 . 9 . 3217–3224 . 10.1002/ps.5877 . 32358830.
  46. Altman . S. . 2014-01-03 . Antibiotics present and future . FEBS Letters . 588 . 1 . 1–2 . 10.1016/j.febslet.2013.10.048 . 24252220 . 2014FEBSL.588....1A.
  47. Web site: Popenoe . Juanita . Diepenbrock . Lauren . Citrus Industry Magazine . Citrus Industry Magazine . 2019-04-02 . 2022-07-17.
  48. Web site: Popenoe . J. . Diepenbrock . L. . Citrus Industry Magazine . Citrus Industry Magazine . 2019-04-02 . 2022-07-17.
  49. Web site: Neff . E. . Citrus Industry Magazine . Citrus Industry Magazine . 2019-11-18 . 2024-08-17.

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