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Contacts or sources of information - National Institute of Agronomic Investigation (INIA); Moçambique Industrial
Occurrence & Spread - Carvalho and Mendes (1958) reported for the first time the occurrence of an unknown disease of coconut palm in northern Mozambique. Plumb-Dhindsa and Mondjane (1984) considered such a disease to be lethal yellowing and associated it with a phytoplasma. Following an earlier report by Rao et al. (1995) a survey was jointly conducted by the Department of Plant Protection of the Ministry of Agriculture & Rural Development of Mozambique (DSV) and National Coconut Development Programme of Tanzania (NCDP) to investigate the etiology of the then unknown destructive disease. Using both polymerase chain reaction (PCR) and hybridization techniques, Mpunami and Seguni (1996) confirmed the occurrence of lethal yellowing disease (LYD) of coconut palm in Cabo Delgado, caused by a phytoplasma similar to that found in Tanzania and Kenya. The disease was confined to Cabo Delgado, with highest incidence in the districts of Palma and Mocímboa-da-Praia. (Rao et al., 1995; Rao et al., 1996; Mpunami and Seguni, 1996). In contrast, survey recently conducted showed that LYD is also present in the Zambezia province (SODETEG & CIRAD, 1999), apparently the same disease described by Quadros (1972) but attributed to conditions of soil and water in the root zone.
Typical symptoms of LYD observed include premature nut fall, followed by necrosis of the inflorescence, yellowing and browning of leaves starting from the base of the crown. In advanced stage, the leaves fall down leaving only the trunk, resembling a telephone post. Infected plants die within 4-6 months from first symptoms. Within Zambézia provice, the disease was found in Chinde, Inhassunge, Nicoadala, Namacurra and Maganja-da-costa districts. The highest incidence of LYD was observed in Inhassunge district, particularly Ngonhane-sede, São Domingos and Matulune. High LYD incidence was also observed in Micaune. The lowest incidence of LYD was observed in Mabala and Bajone (Maganja-da-Costa). The incidence of LYD in Macuze was not alarming as only a limited number of trees showed symptoms of the disease.
Within Cabo Delgado provide, LYD is found in Palma, Mocímboa-da-Praia, Mecufi and Pemba. It can be concluded that LYD is becoming a major limiting factor for coconut production in some areas such as Mocimboa-da-Praia, Palma, Inhassunge and Chinde. A strategy needs to be developed to show down the spread of the disease and to reduce its negative impact on coconut production. Presently, MADR intends to develop an integrated pest management project aiming to control both LYD and the rhinoceros beetle. In addition, a study is underway, involving MADR, SOFRTEG/CIRAD, aiming to establish a project on the development of coconut sector in the Zambézia province. So far, LYD has not been reported in Nampula, but further surveys are needed, particularly in Moma (Moma-sede and Larde localities), where the disease was suspected to occur.
(Reproduced from the paper presented by B.S. Nuvanga and J.S. Cumbi at the 2nd International Coconut Workshop for Africa, Mombasa, Kenya, 8 - 12 May 2000)
Currently active areas - dates and places (seek information/confirmation)
Suspected new outbreaks - specify whether confirmed or unconfirmed (reference)
Other palm/plant hosts
New hosts, new vectors, new strains or suspected loss of resistance - confirmed or unconfirmed
Research projects
Rehabilitation/replanting programmes - the Plant Protection Services intend to introduce domestic quarantine to prevent further spread of the disease to the southern provinces, particularly Inhambane, so far free from LYD.
Economic importance/threat -
99/109 Genetic diversity in coconut lethal yellow disease phytoplasmas in East Africa
Lethal diseases of palms occur in several parts of the world. Palm lethal yellowing phytoplasma (EPPO A1 quarantine pest) occurs in the Caribbean, Mexico, Belize and Honduras. Similar phytoplasma diseases are observed in West Africa (Cameroon, Ghana, Nigeria, Togo) and in East Africa (Kenya, Mozambique, Tanzania). Similarities between diseases have led to the assumption that palm lethal yellowing in the Americas and the African lethal diseases were similar. However, important difference in epidemiology and varietal susceptibility suggested differences between pathogens on each continent and also between East and West Africa. Genetic comparisons have previously shown that phytoplasma isolates from East Africa were related but distinct from those in West Africa and the Caribbean (see EPPO RS 97/222, 94/223).
Further genetic comparison have been made between isolates from East Africa. In Tanzania, 22 million coconut trees (Cocos nucifera) are planted along the mainland coast and in the islands of Zanzibar, Pemba and Mafia. The lethal disease was first reported in coconut trees near Bagamoyo (region of Dar es Salaam) at the beginning of this century. The disease has caused extensive damage on the mainland for the last 30 years and now also occurs in Mafia island. However, disease incidence is not identical in all affected regions. In southern regions, it is estimated that 56% palm trees have been killed since 1965 whereas only 8.5% have been affected in northern regions. Using PCR, RFLP and rDNA sequencing, genetic comparison were made between several Tanzanian isolates from regions with low, medium and high disease incidence. Phytoplasma isolates from Kenya (neighbouring region, north of Tanzania) and from Mozambique (neighbouring region, south of Tanzania) were also studied. Phytoplasmas were detected in all diseased samples. Results showed that phytoplasma isolates from Kenya and Tanzania are similar. But they are both distinct from Mozambique isolates, the later being related to West African isolates. No distinction could be made between Tanzanian isolates despite the fact that differences are observed in disease incidence. Differences in disease severity observed in Tanzania cannot be explained by the occurrence of different pathogens, but perhaps by genetic variability in palm tree populations or different insect vectors but more studies are needed.
Source: Mpunami, A.A.; Tymon, A.; Jones, P.; Dickinson, M.J. (1999) Genetic diversity in the coconut lethal yellowing disease phytoplasmas of East Africa. Plant Pathology, 48(1), 109-114.
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