Lethal Yellowing diseases of the coconut palm: an overview

R. Bourdeix1, K. Allou2 and J. L. Konan Konan3

1CIRAD (Centre de Coopération Internationale en Recherche Agronomique pour le développement). Coconut Breeding Section, Marc Delorme Research Station, National Center for Agronomic Research, 07 BP 13 Abidjan, Côte d’Ivoire. Phone: (225) 24 88 72 or (225) 35 32 11, E-mail: roland.bourdeix@cirad.fr; 2Head of Crop Protection Division, Marc Delorme Research Station, National Center for Agronomic Research, 07 BP 13 Abidjan, Côte d’Ivoire. Phone: (225) 24 88 72; 3Head of Breeding Section, Marc Delorme Research Station, National Center for Agronomic Research, 07 BP 13 Abidjan, Côte d’Ivoire. Phone: (225) 24 88 72.

Lethal Yellowing (LY)-type diseases are pandemic diseases that affect the coconut palm (Cocos nucifera L.) and some other 30 palm species including various ornamentals, such as the Manila palm (Adonidia merrilli L.) and the Thurston palm (Pritchardia thurstonii F.J.M.) [1].

Reports of dying coconut palms exhibiting LY-like symptoms date from the last century in the Cayman Islands, Cuba and Jamaica [2]. During the 20th century, extensive damage due to LY was also reported in Cuba, Jamaica, Dominican Republic, Haiti, Bahamas and Florida. The disease spread to the Yucatàn Peninsula of Mexico in the late 1970s and to Belize in 1993. Lethal diseases with symptoms similar to those of LY were reported in the early 1900s from both East and West Africa, including Kenya, Mozambique and Tanzania (lethal disease), Nigeria (Akwa or bronze leaf wilt), and later from Ghana (Cape St. Paul wilt), Togo (Kaincopé disease) and Cameroon (Kribi disease) [3].

It is quite difficult to get a precise evaluation of the losses caused by LY diseases. In Jamaica, the Coconut Industry Board’s records show that out of the 6 million susceptible Jamaica Tall coconut palms in 1961, 90 % had been killed by LY by 1981. In Ghana, about one million coconut palms were killed during the last 30 years [5]. In Togo, by 1964, about 60,000 palms, or 50 % of the coconut groves, were destroyed by the so-called ‘Kaincopé disease’. In Florida, by 1973, at least 20,000 coconut palms (about 6 % of the total) were affected by the disease. In Mexico and Tanzania, thousands of hectares were also destroyed but no precise evaluation is available.

The ‘yellow diseases’ of plants, so named because of the symptoms they cause, were all originally thought to be caused by viruses. In the 1960s Japanese workers showed that mycoplasma-like organisms (MLOs) could be found in the yellow-affected plants and that symptoms could be alleviated by antibiotic therapy [4]. Mycoplasmas are wall-less procaryotes, which can be pathogens of man, animal and plants. To date over 300 plant diseases have been shown to be associated with MLOs, but they have never been cultured in vitro [4]. The term, ‘phytoplasma’ was introduced to describe these MLOs. DNA molecular analysis has shown that the phytoplasmas associated with coconut LY from Africa [5] [6] and the Carribean [7] are similar but not identical.

As early as the 1880s, it was suspected that insects were in some way associated with LY [1]. About 100 years later, the homopteran cixidiid, Myndus crudus V.D., was identified as the vector in the Caribbean region [5]. In West Africa, another cixidiid, Myndus adiopodoumeensis, is also suspected to be a vector.

For the coconut palm, the progressive symptoms of LY are mainly the following [6]:

  1. premature drop of most of the fruit regardless of their development stage
  2. blackening of newly opened inflorescences
  3. ascending yellowing of the leaves (from the lower to the upper)
  4. spear leaf death and collapse, with possibly a few green leaves remaining
  5. fall of the whole crown, leaving a bare trunk or ‘telephone pole’

Infected palms usually die within 3 to 7 months after the appearance of the first symptom [1].

When the nature of the causal agent was discovered, antibiotic injections were tested in Florida and Jamaica. It was found that the tetracycline group antibiotics suppressed symptom development if applied before leaf yellowing. However, this chemotherapy was not applied on a commercial scale because of its high cost. Removal of diseased palms can reduce the spread of the disease, but this does not eradicate it.

The most efficient way to deal with LY is by replanting with resistant coconut palms. The recent book, Tropical perennial crops diseases, published in 1999 by CIRAD (France), gives a good overview of this subject [7]. Malayan Dwarfs (of yellow-, red-, or green-fruited types) were the first cultivars identified as tolerant to LY during the 1950s in Jamaica. They have been planted on a large scale in that country and in Florida. However, these dwarfs were found to be quite sensitive to other environmental stresses such as drought, insect attacks, or hurricanes. They were progressively replaced by a new tolerant hybrid called ‘Maypan’, obtained in Jamaica by crossing the Malayan Dwarf (red and yellow types) as female and the Panama Tall as male.

In Tanzania, A total of 48 imported cultivars are being screened at four sites, alongside two local “dwarf” populations and 30 populations of the local East African Tall (EAT). To date, all imported cultivars, including those reported to be resistant in Jamaica, are highly susceptible to the disease, although promising levels of tolerance are said to be observed in the local Pemba Red Dwarf and some populations of EAT.

Varietal screening tests have also been conducted in Ghana since the 1980s. Up to now, 27 cultivars have been tested. The most tolerant cultivars identified are the Green Dwarf from Sri Lanka and the Vanuatu Tall. Another screening test using mainly local cultivars is also currently being conducted in Mexico, but the results have not yet been published.

References

[1] Mc Coy, R. E. 1983. Lethal Yellowing of palms. Bulletin 834, University of Florida, Gainesville, Florida, USA.

[2] Arrellano, J. and C. Oropeza 1995. Lethal Yellowing. In: Lethal Yellowing: research and pratical aspects. C. Oropeza, F. W. Howard and G. R. Ashburner (eds.). Kluwer Academic Publisher, The Netherlands.

[3] Eden-Green, S. J. 1997. History, world distribution and present status of lethal yellowing-like diseases of palms. In: Proceedings of an International Workshop on Lethal Yellowing-like Diseases of Coconut. Elmina, Ghana, November, 1995. Eden-Green S. J. and Ofori F. (eds.). Natural Resources Institute, Chatam, UK.

[4] Jones, P.. 1997. History and biology of yellow diseases and phytoplasmas. In: Proceedings of an International Workshop on Lethal Yellowing-like Diseases of Coconut. Elmina, Ghana, November, 1995. Eden-Green S. J. and Ofori F. (eds.). Natural Resources Institute, Chatam, UK.

[5] Dollet, M., and J. Giannotti. 1976. Maladie de Kaïncopé, présence de Mycoplasmes dans le phloème de cocotiers malades. Oléagineux 31 (4): 169-171.

[6] Dollet, M., J. Giannotti, J. L. Renard, and S. K. Ghosh, 1977. Etude d'un jaunissement létal des cocotiers au Cameroun: la maladie de Kribi. Observations d'organismes de type mycoplasmes. Oléagineux 32 (7): 317-322.

[7] Beakbane, A. B., C. H. W. Slater, and A. F. Posnette. 1972. Mycoplasmas in the phloem of coconut, Cocos nucifera L., with lethal yellowing disease. Journal of Horticulture Science 47: 265.

[8] Howard F. W., Norris R. C., and Thomas D. L. 1983. Evidence of transmission of palm yellowing agent by a planthopper, Mindus crudus (Homoptera; Cixidiidae). Tropical Agriculture (Trinidad) 60: 168-171.

[9] Renard, J. L. 1999. Symptomatology and economic incidence. In: Les maladies des cultures pérennes tropicales. D. Mariau (ed). Collection Repères, CIRAD, Montpellier, France.

[10] De Franqueville, H. 1999. Varietal Resistance. In: Les maladies des cultures pérennes tropicales. D. Mariau (ed.). Collection Repères, CIRAD, Montpellier, France.

Figures

Coconut palms with various 
symptoms of LY.

Coconut grove in Ghana badly affected by LY.

Photos by Dr. Hubert de Franqueville, phytopathologist, CIRAD.

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