ProMED
http://www.promedmail.org

Source: European Plant Protection Organisation (EPPO) Reporting Service 01/2024/014 [summ. Mod.DHA, edited]
https://gd.eppo.int/reporting/article-7764

_Candidatus_ Phytoplasma palmicola, one of the phytoplasmas causing lethal palm yellowing diseases (EPPO A1 List), is reported for the first time from Equatorial Guinea. During the past 2 decades, a high mortality of coconut palms (_Cocos nucifera_) has been observed in the coastal areas of Equatorial Guinea, dramatically decreasing coconut production. A survey was carried out in 2021 to identify the cause of the mortality.

Symptomatic coconut palms were sampled, as well as 2 oil palms (_Elaeis guineensis_) showing skirting of the older leaves. Molecular analyses and sequencing were conducted and _Ca._ P. palmicola was detected in the 2 palm species. Phylogenetic analyses showed that the strain present in Equatorial Guinea is identical to the strains from Mozambique, but different to the strains in Ghana and Côte d'Ivoire, confirming the presence of a geographic differentiation among phytoplasma strains in the coastal areas of Western and Central Africa.
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Communicated by:
ProMED

[A range of yellowing diseases of coconut and other palms caused by phytoplasmas are known. The pathogen of lethal decline (LD) disease in Mozambique was classified in 2014 as the reference strain for a novel taxon, _Candidatus_ Phytoplasma palmicola (CPpc; 16SrXXII; see ProMED post 20140621.2556066 and link below; now named Nigerian coconut lethal decline group). CPpc has been reported from several countries in West Africa as well as from Mozambique, where it has destroyed a large number of palms in the east coast coconut belt. The group also includes the pathogens of Cape St Paul wilt (CSPW) in Ghana, the "maladie de Kaincope" in Togo, Bogia wilt in Papua New Guinea and Awka disease (lethal decline) in Nigeria. Strains from Mozambique have since been attributed to a subgroup A (16SrXXII-A), and CSPW phytoplasma strains to a subgroup B (16SrXXII-B).

Lethal yellowing (LY) diseases described from, for example, the Caribbean and Latin America are caused by strains of _Ca._ P. palmae (16SrIV). The phytoplasmas causing Weligama wilt in Sri Lanka and Kerala wilt in India are as yet unclassified. Some of the pathogens may also affect herbaceous crops, such as banana or cassava (e.g., ProMED posts 20180207.5613931 and 20170713.5168553). Commercial control of these diseases relies on resistant varieties, but an unexplained breakdown of LY resistance of some widely used hybrids (ProMED post 20070522.1643) is causing great concern.

LD/LY disease incidence and rate of symptom progression may vary in different areas; palms die over a period of time. Additional phytoplasmas have been identified in infected palms, but their contribution to disease needs further clarification. Other palm species (such as oil palm) may also be hosts of the pathogen(s). Some potential insect vectors have been identified. Quarantine restrictions are in place for the movement of coconut materials to protect areas still free from LD/LY diseases. Some success with replanting certain coconut varieties in affected areas has been reported (ProMED post 20100910.3262).

Maps
Africa (overview):
https://www.worldatlas.com/r/w960-q80/webimage/countrys/africa/maps/africa.jpg

Pictures
Coconut CPpc LD symptoms, Mozambique:
https://borgenproject.org/wp-content/uploads/mozambiques_coconut_groves2.jpg
LY symptoms on coconut:
https://bugwoodcloud.org/images/768x512/1504005.jpg and
http://www.cphdforum.org/wp-content/uploads/2015/06/LethalYellowingCoconutSymptom.jpg (fruit)

Links
Source publication:
https://doi.org/10.1111/aab.12854
Information on _C._ P. palmicola:
https://gd.eppo.int/taxon/PHYPPL and
https://doi.org/10.1099/ijs.0.060053-0
Information on Mozambique coconut LD:
https://agritrop.cirad.fr/543456/,
https://www.ajol.info//index.php/acsj/article/view/135938 and
https://www.researchgate.net/publication/303899031_Coconut_Lethal_Yellowing_Phytoplasma_Disease_in_Mozambique_Diversity_Host_Range_and_the_Impact_of_Farming_Practices_on_Disease_Incidence
Information on palm lethal yellowing phytoplasmas:
https://gd.eppo.int/taxon/PHYP56
Review and diagnosis of palm phytoplasmas:
https://doi.org/10.3389/fpls.2016.01521
Phytoplasma 16SrXXII-A subgroup taxonomy:
https://www.uniprot.org/taxonomy/1775905
Other phytoplasma taxonomy via:
http://www.uniprot.org/taxonomy/33926
Phytoplasma resource centre:
https://plantpathology.ba.ars.usda.gov/phytoplasma.html
EPPO A1 list:
https://www.eppo.int/ACTIVITIES/plant_quarantine/A1_list
- Mod.DHA