Source: FreshPlaza [abridged, edited]
Costa Rica's State Phytosanitary Service (SFE) has updated the requirements for the entry of avocados from Honduras after authorities detected sunspot disease, a quarantine disease not present [controversial, see comments below - Mod.DHA] in the country, in 5 different shipments.
From now on, Costa Rica will require all avocados from Honduras to undergo a molecular laboratory analysis to rule out the presence of the pest. The shipments will be retained awaiting the results. If the viroid is detected, the shipments will be returned.
Honduras is currently Costa Rica's main supplier of Hass avocado after the country banned the entry of this fruit from Mexico, Australia, Spain, Ghana, Guatemala, Israel, South Africa, Venezuela, and the US state of Florida in 2015 to prevent the entry of the sunspot disease. The 2015 measure caused a trade clash with Mexico, the resolution of which is currently in the hands of the WTO [World Trade Organization].
[_Avocado sunblotch viroid_ (ASBVd; currently the only member of genus _Avsunviroid_) affects avocado (_Persea americana_) and a few other members of the family Lauraceae. It causes one of the major diseases of the crop, with serious reductions of yield (up to 95 per cent losses), fruit quality, and tree vigour. Symptoms may include yellowish, depressed streaks on young twigs and fruits, which can look like they are sunburnt ('sunblotch'), as well as, occasionally, vein yellowing on leaves, and bark cracking. However, symptoms may not be visible in some trees, but these still show significant yield reduction and act as pathogen reservoirs.
ASBVd is transmitted with infected budwood or rootstocks for grafting, by cutting tools, pollen (via pollinating bees), and with seed. Asymptomatic trees have an extremely high rate of seed transmission of up to 100 per cent, the resultant infected seedlings are also asymptomatic. Disease management relies on the use of certified viroid free grafting material and seeds. Reliable diagnosis requires molecular techniques. Orchards should be tested every 3 years and pathogen reservoirs, with or without symptoms, must be removed. The viroid has been reported from most avocado-growing areas, including Mexico (where avocado is thought to have originated) and other countries in the Americas.
There appears to be an ongoing argument between countries in Central and South America about where ASBVd is present and what risk it poses to trade. In Costa Rica, ASBVd has been reported to be present before 2003, but it is not clear whether those records refer to commercial plantations. In contrast, its absence has been claimed in 2019 by the National Plant Protection Organisation, but this is being disputed by producers (ProMED post 20160211.4014278) because it was said to be based on surveys for symptoms, not on molecular diagnosis (see European Plant Protection Organisation, EPPO link below).
Even for countries where the viroid is already present, introduction of new strains or spread to new areas must be avoided. Since germinating seeds of commercially purchased avocado fruit is easy for anyone, for example for the home garden, and considering the extremely high rate of seed transmission of ASBVd, introduction of the viroid from an infected area by traded fruit would be almost a certainty over a period of time.
To protect national avocado industries, regular and reliable testing by molecular methods and certification of source orchards would be a minimum requirement to lower the risk of commercial trade of avocado fruit between countries.
The Hass avocado variety is available all year round and accounts for about 80 per cent of avocados eaten worldwide. It arose from a spontaneous mutation in a US garden in the 1920s and carried a patent until 1952.
Costa Rica provinces:
ASBVd, fruit symptoms:
ASBVd, leaf, and bark symptoms:
Information on avocado sunblotch disease and pathogen:
http://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=8083 (with distribution map),
Controversial records of ASBVd in Costa Rica via:
Viroid taxonomy via:
Information on Hass avocado variety: