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 dIvoire. 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 dIvoire. Phone: (225) 24 88 72;
3Head of Breeding Section, Marc Delorme Research Station, National
Center for Agronomic Research, 07 BP 13 Abidjan, Côte dIvoire. 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 Boards 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]: 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. [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 Coconut grove in Ghana badly affected by LY. This site is copyrighted © 1998, 1999, 2000, Palm & Cycad Societies of
Florida (PACSOF)
References
symptoms of LY.
Photos by Dr. Hubert de
Franqueville, phytopathologist, CIRAD.
PACSOF
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