ProMED

Source: Daily News [summ. Mod.DHA, edited]
http://www.dailynews.lk/2021/12/15/local/267456/disease-affecting-coconut-crops-brought-under-control

Nearly 300 000 fruit-bearing coconut trees in the Matara district were cut down due to the spread of the disease affecting coconut cultivations in the district, the Coconut Cultivation Board said. Owners of the trees have been compensated.

Cutting down diseased trees and banning the transport of all raw materials relating to coconut products from and through the affected areas has made a positive impact in controlling the spread of the disease. Growers and landowners have been instructed as to the urgent need of informing officials if they notice any disease symptoms in their trees. Every endeavour possible is currently being made by the Coconut Cultivation Board to prevent the spread of this disease.
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Communicated by:
ProMED
<promed@promedmail.org>

[The disease referred to above is Weligama wilt which was first identified in Matara district in the mid-2000s and has been spreading in southern and western Sri Lanka since. The causal pathogen was found to be a phytoplasma, likely related to other palm yellowing pathogens but it is as yet unclassified. Symptoms have been described as flaccidity and marginal necrosis of leaflets, as well as intense yellowing of fronds, similar to Kerala wilt of coconut in India (e.g. see ProMED post 20210819.8605925).

A range of yellowing diseases of coconut and other palms caused by phytoplasmas are known from different regions. They include members of the 16SrIV (_Candidatus_ Phytoplasma palmae; lethal yellowing, LY; Americas; for more information see ProMED post 20210618.8456768) and 16SrXXII (_Ca._ P. palmicola; several lethal declines Africa, Asia). The phytoplasma causing Kerala wilt in India also still remains to be classified.

Phytoplasmas are spread by sap sucking insect vectors and via cutting or grafting wounds. Some of the palm pathogens may also affect herbaceous crops, such as banana or cassava (e.g., ProMED posts 20180207.5613931 and 20170713.5168553). Herbaceous hosts may possibly serve as pathogen reservoirs for infection of palms. Individual trees may be protected by regular trunk injections of antibiotics (e.g. tetracycline). Commercial control of the diseases mostly relies on phytosanitation (as reported above), followed by replanting with resistant varieties. However, an unexplained breakdown of LY resistance of some widely used hybrids (ProMED post 20070522.1643) is causing great concern.

Maps
Sri Lanka:
https://legacy.lib.utexas.edu/maps/middle_east_and_asia/sri_lanka_pol01.jpg
Sri Lanka districts:
https://qph.fs.quoracdn.net/main-qimg-6c4fd415866ac73f210fbf339ea70689

Pictures
Weligama wilt symptoms:
https://www.bspp.org.uk/wp-content/uploads/2021/03/Chamini-Kanatiwela-Coconut-plantation-affected-with-Weligama-Coconut-Leaf-Wilt-Disease-Matara-Sri-Lanka.jpg,
https://news.lk/media/k2/items/cache/5e6cdcb268db756e4dc23fec27d877da_XL.jpg and
https://www.researchgate.net/profile/Lalith-Perera/publication/276284286/figure/fig2/AS:667667446911000@1536195732649/WCLWD-affected-coconut-palms-showing-flaccidity-A-and-intense-yellowing-symptoms-B_Q320.jpg

Links
Information on Weligama wilt:
http://dx.doi.org/10.4454/jpp.fa.2012.009 (detection of a phytoplasma cause),
https://www.researchgate.net/publication/276284286_Detection_of_Weligama_coconut_leaf_wilt_disease_in_Sri_Lanka_by_polymerase_chain_reaction,
https://www.bspp.org.uk/establishment-of-loop-mediated-isothermal-amplification-for-detection-of-weligama-coconut-leaf-wilt-disease/ and
https://news.lk/news/business/item/3470-rs-450-million-paid-for-felling-coconut-trees-infected-with-leaf-wilt-disease
Affected areas in Sri Lanka:
https://www.researchgate.net/profile/Lalith-Perera/publication/276284286/figure/fig3/AS:667667446906895@1536195732871/Map-of-Sri-Lanka-showing-major-coconut-growing-areas-and-the-disease-area_Q320.jpg
Review and diagnosis of palm phytoplasmas:
https://doi.org/10.3389/fpls.2016.01521
Weligama wilt phytoplasma taxonomy:
https://www.uniprot.org/taxonomy/522451
Other phytoplasma taxonomy via:
http://www.uniprot.org/taxonomy/33926
Phytoplasma resource centre:
https://plantpathology.ba.ars.usda.gov/phytoplasma.html (incl. vector information)
- Mod.DHA