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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Publications at this Location » Publication #324470
Research Project: Quality, Shelf-life and Health Benefits for Fresh, Fresh-cut and Processed Products for Citrus and Other Tropical/Subtropical-grown Fruits and Vegetables

Location: Citrus and Other Subtropical Products Research

Title: Huanglongbing: Devastating disease of citrus

Author
item McCollum, Thomas
item Baldwin, Elizabeth - Liz

Submitted to: Horticultural Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2015
Publication Date: 11/28/2016
Citation: McCollum, T.G., Baldwin, E.A. 2016. Huanglongbing: Devastating disease of citrus. Horticultural Reviews. 44:315-361.

Interpretive Summary: Citrus greening or Huanglongbing (HLB) disease is devastating the citrus industry worldwide, from Asia to the Americas. The only major citrus regions free of this disease are the Mediterranean and Australia/New Zealand. To date there is no cure, no resistance and no therapy used commercially for HLB and production rapidly becomes unsustainable once an orchard is infected due to poor yield. In addition, the fruit and juice products become unmarketable due to problems of flavor, size reduction and poor color. HLB is associated with a bacteria that is spread by a small insect. The disease was discovered in Florida in 2005 and since then orange fruit yields have dropped from around 150 million boxes to what is now predicted to be 69 million for the current season. Management strategies for both the trees and the flavor of orange juice are discussed as well as the physiological effect of the disease on citrus trees.

Technical Abstract: Citrus greening or Huanglongbing (HLB) disease is devastating the citrus industry worldwide, from Asia to the Americas. The only major citrus regions free of this disease are the Mediterranean and Australia/New Zealand. To date there is no cure, no resistance and no therapy for HLB and production rapidly becomes once an orchard becomes unsustainable due to poor yield. In addition, the fruit and juice products become unmarketable due to problems of flavor, size reduction and poor color. HLB is associated with a three species of gram negative alpha proteobacters, Candidatus liberibacter asiaticus (CLas), Candidatus Liberibacter americanus (CLam) and Candidatus Liberibacter africanus (CLaf). CLas and CLam are vectored by the Asian citrus psyllid (Diaphorina citri) and CLaf is vectored by the African citrus psyllid (Trioza erytreae). Management of HLB in the orchard involves identification and removal of CLas-infected trees and aggressive psyllid control. Many citrus, growers are applying additional fertilizers, foliar sprays of micronutrients and compounds that affect plant defense responses, along with special attention to irrigation to prolong the life of trees that are in decline. Other therapeutic strategies being evaluated include thermal and antimicrobial treatments, but these have yet to be applied on a large scale due to practicality of implementation and/or regulatory hurdles. Some tolerant rootstock and scion varieties have been identified and are finding their way into growers’ hands. These varieties have the potential to slow the rate of HLB progression in CLas-infected trees. Citrus juice processors are managing flavor issues by sorting out symptomatic fruit, blending HLB-affected juice with healthy juice, adding citrus aroma to mask off-flavor and debittering juice. The cure for this disease will likely be a transgenic approach inserting several genes imparting tolerance or resistance to the pathogen while making it difficult for the pathogen to in turn develop resistance. Then it will be a matter of consumer acceptance.