| 词条 | Draft:Citrus Blight |
| 释义 |
Citrus BlightCitrus Blight is a detrimental disease of citrus observed in Florida, Brazil and Argentina (the disease is found in many citrus-producing regions including North America, the Caribbean, South America, South Africa and Australia).[1] Although the disease has been identified for more than a century, it has demonstrated difficulties to understand its causes, set of causes, or manner of causation and its causal agent remains up in the air and unable to be identified.[2] Given that the symptoms of Blight are very broad and may be confused with those associated with other diseases and given that the causal agent is unknown, the diagnosis of Blight is complicated and relies on [https://medical-dictionary.thefreedictionary.com/indirect+assay indirect assays].[1] The early research regarding the etiology of Blight was performed in Florida. There were implications of a biotic agent provided by the evidence of its transmissibility through root grafting.[4] In contrast, efforts at transmission by grafting foliar parts (twigs, buds, leaves) failed and so did attempts to spread the disease by use of vegetative propagation materials.[5] Further efforts to propagate the disease with cuttings or bud grafts from already infected Blight-affected trees were also thoroughly negative, leading to the assumption that the causal agent of citrus Blight is located or restricted to the roots.[4] A full list of citrus diseases can be found here. Identification [1]Step one: Drill a hole into the trunk of the tree above the bud union using a sharp drill bit and a battery powered drill. The hole should be at least one inch deep into the tree trunk. Step two: Fill the syringe with water, making sure all the air within the syringe is purged before inserting the tip of the syringe into the tree trunk. Step three: Insert the tip of the syringe into the drilled hole, making sure that a tight fit between the tree trunk and syringe tip exists. Apply pressure to the syringe to see if water is accepted by the tree. As water is accepted, one can see the plunger of the syringe move slightly forward. Healthy trees with no visual symptoms in the canopy should accept at least 3 ml in 10 seconds, whereas fully blighted trees will accept less than 0.5 ml of water in the same 10 second period. Trees in early stages of the disease will accept 1 to 2 ml per 10 seconds. Trees infected with blight will accept very little or no water, whereas a tree declining from other diseases or disorders will accept water readily, thus providing an easy field diagnostic test for citrus blight. Detailed pictures can be seen here Geographical Distribution [6]Asia: Turkey Africa: Mozambique, South Africa. North America: USA (Florida, Hawaii, California) Central America and Caribbean: Cuba, Dominican Republic South America: Argentina, Brazil, Colombia, Suriname, Uruguay, Venezuela Oceania: Australia (Queensland) EU: Not present Symptoms and Age of OnsetTrees usually do not show symptoms of blight and grow normally until they reach five to six years of age or older. Then, trees begin to wilt and to show leaf loss, reduced growth flushes, die back and general decline.[7] During the early stages of blight, the symptoms may be limited to one part of the tree and eventually develop into the entire tree. Trees persist in various degrees of waning and become unproductive, however they seldom die. During the process of tree decline, vegetative sprouts may be formed on the trunk and on larger inner branches nearby the trunk.[8] Along with that, water uptake in the xylem is degraded, zinc accumulation begins in the bark and outer xylem tissue, and zinc deficit patterns start in the leaves.[9] As xylem vessels in the trunk become clogged with unstructured obstructions, water transport is reduced, causing a wilt to develop. New xylem vessels are produced at a higher rate but are significantly smaller in size and causing them to eventually become blocked.[9] Blight impacts all major rootstocks and seedlings to varying levels but is most damaging to rough lemon, Rangpur lime, trifoliate orange and citrange rootstocks. Trees grown on sweet orange, sour orange, mandarin and some citrumelo rootstocks usually have lower incidences of blight and typically do not exhibit symptoms before trees are 15 to 20 years old.[9] Indicating that these rootstocks could have [https://academic.oup.com/bioscience/article/49/12/1009/246892 legacy affects].[10] SpreadAfter blight first appears within a grove, there is no strict pattern of infection in the trees.[9] The disease spreads to adjacent trees within the orchard rows more frequently than across rows. Blight has not been transmitted by ordinary budding or grafting practices.[7] Although, grafting roots of trees know to be infected to healthy individuals will cause the tree to develop blight symptoms in about two years. Natural root grafting of adjacent trees has been associated with the spread of the disease.[11] All these observations lead researchers to believe that the pathogen is root associated but causes [https://www.britannica.com/science/systemic-symptom systemic symptoms]. Economic ImpactCitrus blight is a serious economic threat that causes complications for citrus growers in Florida, Brazil, and many other countries around the world. Brazil is the largest citrus producer in the world, being responsible for greater than 20% of total production.[7] However, this is still considered low and below capacity due to production losses associated with citrus blight.[7] Millions of citrus trees become fruitless every year, with yearly loss rates of 4-7% in affected orchards.[2] In Florida, losses are estimated at 500,000 trees per year.[2] This disease impacts many geographic regions and causes trees to become unproductive, causing losses in excess of $60 million every year.[1] This figure does not include the loss in yield observed in the first few years of onset, these numbers are from complete loss of a productive tree. Control MeasuresSince there is no known cure for citrus blight, once trees begin to decline, they never fully recover.[12] Intense pruning of blighted trees will result in temporary vegetative recovery, but once they show increase in production, they begin to develop effects of the disease again. The only recommended procedure for management of citrus blight is as follows[13] : 1. Remove trees quickly, once the yield of affected trees has declined to uneconomic levels. 2. Plant or replace trees with trees on rootstocks such as Cleopatra mandarin or Swingle citrumelo that do not develop blight at an early age.[14] 3. Plant trees on vigorous, productive rootstocks such as Carrizo citrange or rough lemon, which develop blight at an early age, and replace trees that decline as soon as they become unproductive. Production can be maintained at relatively high levels in spite of blight with these stocks.[13] There are no chemical treatments available for use, so “treatment” of this disease does not have negative connotations in respect to ecological and ecosystem impacts. References =1. ^1 2 3 Futch, S., Derrick, K., and Brlansky, R. (2017). Field Identification of Citrus Blight. Retrieved September 9, 2018, from http://edis.ifas.ufl.edu/pdffiles/HS/HS24100.pdf 2. ^1 2 Jeger, M., Bragard, C., Caffier, D., Chatzivassiliou, E., Dehnen‐Schmutz, K., Gilioli, G., . . . Candresse, T. (2018). Pest categorisation of ‘Blight and blight‐like’ diseases of citrus. EFSA Journal, 16(4). doi: 10.2903/j.efsa.2018.5248 3. ^1 2 Garnsey, S. (2004). Horticultural Research Laboratory [USDA employee field pictures]. Retrieved September 27, 2018, from https://www.forestryimages.org/browse/autimages.cfm?aut=20741 4. ^1 Derrick, K. S., & Timmer, L. W. (2000). Citrus Blight and Other Diseases of Recalcitrant Etiology. Annual Review of Phytopathology, 38(1), 181-205. doi:10.1146/annurev.phyto.38.1.181 5. ^Burnett, H. C., Nemec, S., & Patterson, M. (2008). A review of Florida citrus blight and its association with soil edaphic factors, nutrition andFusarium solani. Tropical Pest Management, 28(4), 416-422. doi:10.1080/09670878209370749 6. ^CABI and European and Mediterranean Plant Protection Organization. Citrus Blight disease. Retrieved from https://gd.eppo.int/download/doc/76_datasheet_CSB000.pdf. 7. ^1 2 3 Renato de Abreu, J., Paiva, L. V., Rodríguez, M. A., Silva, A. T., Henriques, A. R., & Chalfun-Junior, A. (2015). Identification and Quantification of Differentially Expressed Genes Associated With Citrus Blight (Citrus spp.). Ciência E Agrotecnologia, 39(1), 32-38. doi:10.1590/S1413-70542015000100004 8. ^Palwasha, A., & Khan, Y. S. (2013). Plantwise Knowledge Bank. Retrieved September 10, 2018, from https://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=13441 9. ^1 2 3 BIOSECURITY SA – Plant Health. (2017). Citrus Blight disease. Retrieved from http://www.pir.sa.gov.au/__data/assets/pdf_file/0019/297001/Fact_Sheet_-_Citrus_Blight_-_July_2017.pdf 10. ^Moorhead, D. L., Doran, P. T., Fountain, A. G., Lyons, W. B., Mcknight, D. M., Priscu, J. C., . . . Wall, D. H. (1999). Ecological Legacies: Impacts on Ecosystems of the McMurdo Dry Valleys. BioScience, 49(12), 1009-1019. doi:10.1525/bisi.1999.49.12.1009 11. ^Zhang, Y., Barthe, G., Grosser, J. W., & Wang, N. (2016). Transcriptome analysis of root response to citrus blight based on the newly assembled Swingle citrumelo draft genome. BMC Genomics, 17(1). doi:10.1186/s12864-016-2779-y 12. ^Schneider, W., Roy, A., Shao, J., & Briansky, R. (2015). Citrus blight research update. Retrieved September 11, 2018, from https://crec.ifas.ufl.edu/extension/trade_journals/2015/2015_December_blight.pdf. 13. ^1 Roberts, P., Brlansky, R. (2016). 2016 Florida Citrus Pest Management Guide: Blight. Retrieved September 11, 2018, from https://edis.ifas.ufl.edu/pdffiles/CG/CG03800.pdf 14. ^Mccollum, G., & Bowman, K. D. (2017). Rootstock Effects on Fruit Quality among ‘Ray Ruby’ Grapefruit Trees Grown in the Indian River District of Florida. HortScience, 52(4), 541-546. doi:10.21273/hortsci11435-16 |
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