A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Mon 24 Feb 2020
Source: FreshPlaza, Diario El Mundo (Salvador) report [edited]
The Ministry of Agriculture and Livestock (MAG) of El Salvador has declared a phytosanitary emergency due to huanglongbing (HLB) [citrus greening disease] that is affecting the country's citrus. [MAG] have initiated a control and eradication plan, which consists of taking samples across the country to learn about the situation of plantations and the extent to which production [is] affected. The plan also involves conducting tests and diagnoses, strengthening the laboratory network, and prohibiting the sale of uncertified plants.
The Government said that this disease was detected in previous years, but past administrations hid the problem. MAG said that the pest was first detected in 2013. The disease has already been officially detected in countries of the region such as Guatemala (2009), Honduras (2010), Nicaragua (2010), Costa Rica (2011), and Belize (2009) [see ProMED-mail posts 20110223.0593, 20100419.1272, 20090518.1853].
[Greening is one of the most damaging diseases of citrus crops affecting leaves and fruit. It is caused by fastidious phloem-inhabiting bacteria classified as _Candidatus_ Liberibacter asiaticus (CaLas; Asian greening; huanglongbing), africanus (including a subsp. capensis; African greening) or americanus (South American greening). The 3 pathogens can only be distinguished by molecular methods. Several phytoplasma species have been reported to cause symptoms similar to greening disease in citrus and coinfections of phytoplasmas with CaLas have also been recorded (see ProMED-mail posts 20180214.5629251 and 20190329.6392077). Further research is needed on symptomatology, epidemiology, and host impact of both single and mixed infections of these pathogens.
Symptoms include blotchy mottling and yellowing of leaves, as well as small, irregularly shaped fruits with a thick, pale peel and bad taste. Early symptoms may be confused with nutrient deficiencies. Affected trees become stunted, bear multiple off-season flowers and may live for only a few years without ever bearing usable fruit. The diseases are restricted to _Citrus_ and close relatives because of the narrow host range of their psyllid vectors. The pathogens can also be spread by grafting and possibly by seed from infected plants or transovarially in the vectors. Both pathogens and vectors can be spread with plant material.
Disease management requires an integrated approach including use of clean planting and grafting stock, elimination of inoculum, use of pesticides for vector control in orchards, as well as chemical or biological control of vectors in non-crop reservoirs. Control using cultural methods, such as interplanting with non-host crops, is being trialled. In areas where a pathogen has not yet been detected, biological control of vectors has been used successfully to reduce insect numbers and, therefore, the risk of greening outbreaks (for example, see ProMED-mail post 20090601.2034).
Antibiotics as leaf sprays, seed treatments, or trunk injections are being used occasionally to treat citrus greening (see for example, ProMED-mail posts 20181119.6154764 and 20190320.6377319), but are subject to strict regulations in most countries due to their associated risks of facilitating the emergence of antibiotic resistances in other crop, animal, and human pathogens. Furthermore, beneficial soil microbes may be killed off as collateral damage, making the plants weaker and more susceptible to other diseases. Residues of antibiotics may also lead to rejection of exported produce by some countries.
http://www.lib.utexas.edu/maps/americas/elsalvador.jpg (with departments)
Central America, overview:
Citrus greening symptoms, leaves, and branches:
Citrus greening, fruit symptoms:
Asian and African greening, symptoms and vector photo galleries:
https://gd.eppo.int/taxon/LIBEAF/photos (African) and