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Occurrence - Cape St Paul Wilt disease was named from an eastern coastal location in Ghana where reports of dying coconuts apparently date back to the 1930s (Westwood, 1953; Martyn, 1954; Leather, 1956 & 1959). In 1975 material was collected in this region, from which MLO were identified (Dabek et al, 1976).
Spread - Despite only being reported from one area for 40 years, the disease did spread and in 1975 a previously undocumented outbreak was identified in the Western region at Cape Three Points (Johnson & Harries, 1976). Subsequently, it was claimed that the Cape Three Points outbreak had first been detected in 1964 (Ofori & Nkansah-Poku, 1997). Since 1985 new disease foci have developed "at an alarming rate" (Ofori & Nkansah-Poku, 1997) in the major coconut-producing areas of the Western and Central regions. These authors reported that by 1995 it had appeared near Apam in the Central region (half-way back towards Cape St Paul) and to the west it had reached Ampain (halfway to the border with Côte d'Ivoire).
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 - STD III project on the Etiology and Control of Lethal Yellowing-type Diseases of Coconut Palm in Africa and the Iternational Workshop on Lethal Yellowing-like Diseases of Coconut which took place in Elmina, Ghana in November 1995
According to Dery et al, screening for CSPWD tolerance in Ghana started in 1956 (Chona and Adansi, 1970). A more concerted effort at CSPWD resistance screening was started in 1981 with funding from the Government of France under the France/Ghana/Cote d'Ivoire Coconut project. Seven trial plots were set up at various sites in the Western Region (de Taffin & le Saint ,1987). A total of 27 ecotypes were involved. Under the EU-Science and Technology for Development (EC-STD) finding, 2 new plots were added. This brought the total number of ecotypes under test to 38. All the trial plots were planted in a complete randomised block design.
As at September 1999, 5 out of the total 9 plots have been affected by the disease: Cape Three Points, Akwidaa, Dixcove, Agona Junction, and Princess. Results of the Dixcove and Cape Three Points trials were given in Dery et al. (1995) and Mariau et al. (1996). At the time, the disease incidence in Akwidaa was very low (only 3 palms affected) and both Princess and Agona junction were disease-free. This paper presents the results as of September 1999 for the Agona Junction and Akwidaa trials. At Princess, only one palm has so far been attacked by CSPWD. The Akwidaa trial was planted in 1981 in an already devastated area. At the time of planting the disease was no more active in the area. A total of 13 ecotypes were planted here. The Agona Junction trial was planted in 1981-1983 in a non-diseased zone. Twenty-seven ecotypes were planted.
At Akwidaa the disease first appeared in this plot in l988 and, by 1990, three palms had been affected. The disease then disappeared from the plot until 1996 when two palms were infected again. It then started spreading steadily up to date. At Akwidaa, the high yielding hybrid MYD x WAT and another hybrid SGD x WAT have the highest percent infection (69.57%). The next is CRD x WAT (66.67%) and then the control (WAT) (34.55%). So far 37.21% of the total palms planted have been affected by CSPWD. The SGD and MRD have not been attacked.
At Agona Junction a total of 39.56% of the palms planted at Agona Junction have been attacked by CSPWD. The ecotype with the highest percent infection is again the MYD x WAT (91.30%). This is followed by SGD x WAT and MRD x WAT with 70.83% and 59.09% respectively. The MYD shows 58.33% infection. So far the SGD, VTT x VTT, MYD x VTT, MYD x RNT, CRD x RNT and MYD x PYT have not been affected.
The authors state that these results need to be interpreted with caution as the number of palms is small and the disease is still active in the plots, but the results give some indication of which ecotypes might be tolerant.
In addition, according to Mariau et al, the results obtained have sometimes been difficult to interpret, since the coconut palms in the trials suffered substantial mortality right from an early age, due to a severe drought one to two years after planting and severe Oryctes attacks linked to the existence of large numbers of palms killed by the disease in surrounding plantings, which act as larval refuges.
The calculations do not take account of replacement palms, which in many cases are still small and therefore not as vulnerable to the disease. The first cases of the disease were not seen until seven years after planting at Dixcove and ten years after planting at Cape Three Points. For the reasons mentioned above, the number of palms observed was very small in many cases, and the conclusions reached are therefore sometimes provisional.
Overall, the Dwarfs are more tolerant than the Talls, and the SGD (Sri Lanka Green Dwarf) performs particularly well: no deaths have yet been seen out of nineteen individuals. However, the CRD (Cameroon Red Dwarf) is highly susceptible, whilst the MYD performs quite well, although the number of individuals under observation is small, due to this Dwarfs high susceptibility to drought and Oryctes attacks. However, when the west of the country was contaminated, it became clear that the MYD eventually succumbs in the event of very high disease pressure.
All the Talls tested seem to be susceptible, particularly the WAT, which has been devastated by the disease. The VTT (Vanuatu Tall) seems to be an exception, since no cases of mortality have been seen, but the number of individuals observed is small.
All the hybrids tested seem to be susceptible to some degree, but the number of individuals being observed is often too small to draw any conclusions. For example, the MYD x VTT should perform well, given its reasonably or highly tolerant parents. The apparent good performance of the MYD x MLT (Malayan Tall) is more difficult to explain, since the MLT is highly susceptible. The SGD x VTT, which should perform well, was unfortunately not one of the hybrids tested in this first series of trials.
The only way of controlling the disease is to breed tolerant varieties or hybrids. Very few varieties have shown real tolerance, and the level varies depending on disease "pressure". In Ghana, the Malayan Yellow Dwarf performs well, but in the Princess Town region, where the disease has now disappeared after wiping out all the coconut plantations in the are a, this Dwarf was unable to resist destruction, except for a single individual.
Rehabilitation/replanting programmes - Results from containment trials, also carried out by the Oil Palm Research Institute, indicate that hot-fogging with chlorpyrifs followed by cutting of all diseased trees are the most effective method of containing the spread of Cape St. Paul Wilt Disease of coconut.
Economic importance/threat - While the disease was in the eastern, Volta, region it was not perceived as a threat to major coconut growing areas in the Western region. Even when the Cape Three Points outbreak was recognised the disease was ignored because it did not threaten cocoa (the chief cash crop) or palm oil (the chief source of vegetable oil). The opportunity was not taken to use the active disease area in Ghana to screen hybrids produced in neighbouring Côte d'Ivoire BEFORE these were offered to Dominican Republic, Haiti, Indonesia, Mexico, Mozambique or Tanzania (just some of the locations were phytoplasma resistance is necessary).
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