Longan witches broom-associated virus

Longan witches broom-associated virus (LWBD[1] or LWBaV) is a species of positive-sense single-stranded RNA virus that has not been assigned to a genus within the family Potyviridae.[3][2][4] It is thought to be the cause of witch's broom in longan (Dimocarpus longan), a large tropical tree from southeastern Asia of economic value. Longan witches broom disease[2] is a condition that was first described in 1941.[5] The virus was found in symptomatic plants and absent in healthy plants,[2] but not all of Koch's postulates have been fulfilled.[4]

Longan witches broom-associated virus
Virus classification
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Pisuviricota
Class: Stelpaviricetes
Order: Patatavirales
Family: Potyviridae
Genus: incertae sedis
Species:
Longan witches broom-associated virus
Member viruses[1]
  • longan witches' broom-associated virus
Nations and subnational regions in China within which Longan witches broom-associated virus occurs (red)
Genomic information
NCBI genome IDKY649478
Genome size9428 nucleotides
Year of completion2017[2]

Names

The official name for the species of virus is Longan witches broom-associated virus, properly written in italics, capitalized, and with no apostrophe.[3] Within the species, there is one noted member virus, longan witches' broom-associated virus,[1] which is not italicized or capitalized, but does include the apostrophe.[6] In Chinese it is called 龙眼鬼帚病毒[7] (Lóngyǎn guǐzhǒu bìngdú) or 龍眼之本鬼病者[5] (Lóngyǎn zhī běn guǐ bìng zhě). In Vietnamese the disease is called chổi rồng trên nhãn,[8] chổi rồng hại nhãn, bệnh chùn ngọn, bệnh chổi sể, and bệnh hủi nhãn.[9]

Phylogeny

Longan witches broom-associated virus is not closely related to other members of the family Potyviridae.[4][2] The genus it has the closest phylogenetic affinity to is Tritimovirus, but there is no support to include it in that genus[4] or any other established genus, and so its generic placement is currently incertae sedis (uncertain).[2] Instead of comparing sequences of RNA nucleotides directly, transcribing the RNA nucleotide sequence into an amino acid sequence yields Rose yellow mosaic virus (RoYMV),[2][4] the sole member of the monotypic genus Roymovirus, as the closest relative of LWBaV.[3] Further study is needed to determine the precise relationship between RoYMV and LWBaV.[4]

Structure

Virions of Longan witches broom-associated virus are filamentous and average 730 nm in length[2] (300–2,500 nm) and 14–16 nm wide.[7] Inside is a 9,428 nucleotide (excluding the poly(A) tail) positive sense RNA genome with an open reading frame of 9,261 amino acids.[2]

Pathogenesis

Transmission
A litchi stink bug (Tessaratoma papillosa), one of the vectors of the disease

Grafting[10] and seeds can spread the disease,[11][12] so as early as 1955 the cause was thought to be a virus.[13] A virus was found in diseased leaves in 1972,[10] but the report was controversial because electromicrographs were not published and the results were not replicated for some time.[11] This left the possibility that the cause was a species of phytoplasma, twig borer, or other organism.[14] Treating seedlings with benzylpenicillin and tetracycline fails to stop the disease, indicating that phytoplasma are not the cause.[15][16] Twig borers such as Adoxophyes cyrtosema, Conopomorpha sinensis, Crytophlebia ombrodelta, and Hypatima longanae were eliminated as possible vectors or causes as the disease will manifest on branches undamaged by these insects, and the disease will also be absent from damaged branches.[17] A filamentous virus was isolated in 1990,[7] with attributes similar to the one found in 1972.[10]

The disease is spread by litchi stink bug[10] (Tessaratoma papillosa, in the family Tessaratomidae) and longan psylla,[18] (Cornegenapsylla sinica)[12] and the virus was found in the salivary glands of those insects.[15][19] Because of the insect vectors, it is possible the virus is related to one afflicting lychee,[19] and can be spread to that species via grafting.[13] Longan gall mite (Eriophyes dimocarpi)[17] and the dodder Cuscuta campestris spreads the pathogen, as does infected pollen but not sap.[12]

Similar to Rose yellow mosaic virus, the genome of LWBaV does not include conserved aphid transmission motifs, and thus is not thought to be transmitted by aphids.[4] The planthopper Pyrops candelaria also does not seem to spread the pathogen.[19][12]

Susceptible varieties of longan include ‘Youtanben’ (油潭本), ‘Dongbi’ (东壁),[12] ‘Honghezhi’, and ‘Pumingyan’.[20] The cultivars ‘Shuinan no. 1’ and ‘Lidongben’ are highly resistant to LWBD. Fa Hok is susceptible, but more resistant than some others.[10] Grafting with heat-treated[21] or resistant scions is an effective way to reduce disease.[11] However, it is also important to remove infected plant material and control for insect vectors.[12][22] Application of miticides like omethoate, dicofol, or colloid sulphur can dramatically decrease the spread of the disease.[17]

Range

The disease is found in Vietnam,[2] Taiwan, China,[11][11][23] and Cambodia.[24] In China it is found in Hainan, Guangxi, Guangdong, Fujian,[5][13][25][11][23][17] and Hong Kong.[10] It was the first disease of longan ever reported in Hong Kong, and likely was introduced there from planting materials originating from Guangdong.[10]

Afflicted trees can be 20–100% of a grove, with higher percentages found in more mature groves.[11]

Symptoms
Healthy longan foliage

The disease stops young leaves from expanding and distorts mature leaves.[11] Leaves may show vein clearing (yellowed veins),[13] slight blistering, and necrosis.[10] New leaves are smaller, duller, and have rolled margins.[10] Infected leaves are crinkled, narrow, and typically fall off early.[13] Under a microscope, infected affected bud leaflets may have longer trichomes (hairs), but this may be caused by co-infection with mites and not the virus itself.[17] Infected branches have shoots that grow into dense clusters,[11] which display the eponymous 'witches broom.'[10][13] The inflorescences do not extend fully, resulting in distorted flowers[11] with crowded panicles.[10][13] The flowers then produce small, empty fruit if they do so at all.[11] Otherwise the flowers prematurely fall off, leaving a feature looking like a broom.[10][13] Younger trees typically display more symptoms than mature trees.[10]

The virus is only found in the sieve tubes,[15] typically associating with the cell membrane and cell walls and rarely in the lumen.[10] Typically the virions will cluster and not be found singly.[10]

Damage from twig borers such as Hypadima longanae can match the symptoms of LWBD.[26]

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gollark: I expect with enough time the spare capacity would end up retasked for something important, though.
gollark: Are they overclocked to compensate or something?
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References
  1. "Unassigned species in family Potyviridae". International Committee on Taxonomy of Viruses. 28 November 2018. Retrieved 4 September 2019.
  2. Seo, Jang-Kyun; Kim, Mi-Kyeong; Kwak, Hae-Ryun; Kim, Jeong-Soo; Choi, Hong-Soo (September 2017). "Complete genome sequence of longan witches' broom-associated virus, a novel member of the family Potyviridae". Archives of Virology. Springer Vienna. 162 (9): 2885–2889. doi:10.1007/s00705-017-3405-2. ISSN 0304-8608. OCLC 7038037379. PMID 28501954.
  3. "Virus Taxonomy: 2018b Release". International Committee on Taxonomy of Viruses (ICTV). March 2019. Retrieved 4 September 2019.
  4. Wylie, Stephen; Kreuze, Jan F.; Lopez-Moya, Juan Jose; Makinen, Kristiina; Inoue-Nagata, Alice Kazuko; Ohshima, Kazusato; Wang, Aiming (1 May 2018). "Two proposed unassigned species in Potyviridae" (DOCX). International Committee on Taxonomy of Viruses. Retrieved 6 September 2019.
  5. Qiu, Weifan (裘維蕃) (1941). "福建經濟植物病害誌(一)" [Records on diseases of plants of economic importance in Fujian (1)]. 新農季刊 (Quarterly Journal of New Agriculture) (in Chinese). 1 (1): 70–75. OCLC 163828468.
  6. "How to write virus and species names". International Committee on Taxonomy of Viruses. Retrieved 13 September 2019.
  7. Ye, XuDong (叶旭东); Chen, JingYao (陈景耀); Ke, Chong (柯冲) (1990). "Partial purification of a filamentous virus from longan (Dimocarpus longan Lam.) witches' broom diseased trees". Chinese Journal of Virology (in Chinese). 6 (3): 284–285. ISSN 1000-8721. OCLC 823896098.
  8. Viện Cây ăn Quả Miền Nam. "HỘI CHỨNG CHỔI RỒNG TRÊN NHÃN VÀ BIỆN PHÁP QUẢN LÝ" (ppt). Integrated Pest Management Innovation Lab (in Vietnamese). Retrieved 12 September 2019.
  9. "Chổi rồng hại nhãn". Cấm nang Cây Trồng (in Vietnamese). Retrieved 12 September 2019.
  10. So, Vera; Zee, S.-Y. (September 1972). "A New Virus of Longan (Euphoria longana Lam.) in Hong Kong". PANS Pest Articles & News Summaries. en. 18 (3): 283–285. doi:10.1080/09670877209411804. ISSN 0030-7793. OCLC 4642289064.
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  12. Chen, Jingyao (陈景耀); Ke, Chung (柯冲); Xu, Changfan (许长藩); Song, Ruilin (宋瑞琳); Chen, Jingying (陈菁瑛) (15 November 1990). "龙眼鬼帚病的研究 Ⅱ.传病途径" [Studies on Witches’ Broom of Longan II. Transmissive Approaches]. Fujian Journal of Agricultural Sciences (福建农业学报) (in Chinese). 2: 1–6. ISSN 1008-0384. OCLC 859253819. Retrieved 12 September 2019.
  13. Li, Lai-Yung (李來榮) (1955). "龍眼樹的病毒病害的初步研究" [A Virus Disease of Longan, Euphoria longana, in Southeast China]. Acta Phytopathologica Sinica (植物病理學報) (in Chinese). 1 (2). ISSN 0412-0914. OCLC 826612488. Retrieved 12 September 2019.
  14. Li L.R., 1983. Longan Cultivation. Agricultural Press, Beijing, pp. 128-131.
  15. Chen, Jing-Yao (陈景耀); Ke, Chong (柯冲); Xie, Xu-Dong (叶旭东); Li, Kai-Ben (李开本) (April 1994). "龙眼鬼帚病的研究Ⅲ．病毒病原的确认" [Studies on longan witches' broom disease. III. Affirmance of viral pathogen] (pdf). Virologica Sinica (in Chinese). 9 (2): 138–142. ISSN 1995-820X. OCLC 969753161. Retrieved 12 September 2019.
  16. Chen JingYao (陈景耀), Ke Chong (柯冲), Ye XuDong (叶旭东), and Li Kaiben (李开本), 1989. A brief report on the pathogen of longan witches' broom disease. Fujian Agricultural Sciences and Technology (福建农业科技 or 福建農業科技) 5: 42. ISSN:0253-2301 OCLC:63079724 http://eng.oversea.cnki.net/kcms/detail/detail.aspx?filename=FJNK198905032&DBName=cjfqtotal&dbcode=cjfq
  17. He, Dengping; Zeng, Meiling; Zhou, Beipei; Lin, Senxin; Peng, Jianxing; Li, Jiayuan; Huang, Weiming (2001). "Occurrence, Cause and Control of Longan Witches' Broom in Guangdong". Acta Horticulturae (558): 407–412. doi:10.17660/ActaHortic.2001.558.65. ISSN 0567-7572. OCLC 211357761.
  18. Chen J.Y., Xu ChangFan, Li Kaiben (李开本), and Ke Chong (柯冲), 1987. A brief report on the transmission of longan witches' broom disease by insect vectors. Fujian Fruits 3: 63.
  19. Chen, JingYao (陈景耀); Xu, ChangFan; Li, Kaiben (李开本); Xia, YnHua (1992). "Experiments on the transmission of longan witches' broom disease by insect vectors". Acta Phytopathologica Sinica (in Chinese). 22 (3): 245–249. ISSN 0412-0914. OCLC 826612488.
  20. Chen J.Y., Chen J.Y., Xu X.D., Fan G.C. and Chen X., 1998. An investigation into the susceptibility of varieties to longan witches' broom disease and some considerations about the breeding and utilization of resistant varieties. In: Prospects of Plant Protection in The 21st Century. Beijing. S. & T. Press of China. Beijing. pp. 410-413.
  21. Chen J.Y, Chen J.Y., Fan G.C. and Chen X., 1999a. Preliminary study on the elimination of virus of longan witches' broom disease. In: Advances on Plant Pathology (Zhu, Y. W., Li, J. Y. and Wang, H. M. eds). Yunnan S. & T. Publ. House, pp. 163-166.
  22. Chen J.Y., 1990. The spreading period of longan witches' broom disease by insect vectors and their timely control. Fujian Agricultural Science and Technology, 1: 18.
  23. Zhu W.S., Huang H.Y., Huang T.L., Lei H.D. and Jiang Y.H. (eds.), 1994. The Handbook of Diseases and Pests of Fruits in Southern China. Agriculture Press, Beijing. pp. 258.
  24. Tran, Hanh; Van, Hoa Nguyen; Muniappan, Rangaswamy; Amrine, James; Naidu, Rayapati; Gilbertson, Robert; Sidhu, Jaspreet (2019). "Integrated Pest Management of Longan (Sapindales: Sapindaceae) in Vietnam" (PDF). Journal of Integrated Pest Management. 10 (1): 1–10. doi:10.1093/jipm/pmz016. ISSN 2155-7470. OCLC 8163431596.
  25. He Dengping, Zeng Meiling and Zhou Beipei, 1996. A new pest of the longan – preliminary study on the damage incurred and control methods. Natural Enemies of Insects 18: 44.
  26. Ke G.W. and Wang C.C., 1990. Damage symptoms similar to longan witches' broom and a new twig borer – Hypadima longanae sp. nov. China Fruits 2: 37-38.
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