Lethal Diseases of Coconut Palm

 in the Caribbean Region

 Randolph E. McCoy
 University of Florida
 Research and Education Center
 3205 S.W. College Avenue
 Fort Lauderdale, FL 33314 USA


 Lethal diseases of coconut palm in the Caribbean region in-
clude lethal yellowing (LY), hartrot (HR), redring (RR),
budrot, and buttrot. Of these, LY is by far the most impor-
tant. Lethal yellowing occurs in and to the north ofJamaica, in
Florida and Texas, and from the Bahamas to Quintana Roo,
Mexico. The common coconut cultivar of the Caribbean
region, the 'Jamaica Tall' ('Atlantic Tall') is highly susceptible
to LY. LY is associated with a mycoplasma-like organism
which obligately infects the phleom of diseased palms, and is
carried from palm to palm by the leafhopper Hyndus crudus.


HR produces symptoms very similar to LY, but is associated
with flagellated protozoa of the genus Phytomonas, which also
are obligate phloem-inhabitors. HR occurs in South America,
the southern islands of the Caribbean, and in Central
America. The vector of HR is not known with certainty. RR oc-
curs over the same range as HR and occurs with LY in the
Yucatan peninsula. RR is caused by the nematode Radina-
phelinchus cocophilus and its vector is the palm weevil.
Budrot and buttrot, both caused by fungal invasions, annually
cause minor losses in coconut palms throughout the region.


 Three major systemic lethal diseases of coconut palm are pre-
sent in and around the Caribbean Basin. These are redring (RR),
lethal yellowing (LY), and hartrot (HR) or Cedros wilt. In addi-
tion, a number of lesser important diseases of a systemic or lethal
nature may be found, thus leading to some confusion in symp-
tomatology and diagnosis. Two major diseases, LY and HR, are of
very similar symptomology and workers have had to rely on elec-
tron, or phase contrast light microscopy for diagnosis. The third
major disease, RR, is readily distinguished in the field. Minor
losses of coconut palms in all or parts of the region are attributed
to budrot, buttrot, bronze leaf wilt, and lightning strike.
 Early literature describing maladies of coconut palm in the
Caribbean region often confused these various syndromes,
especially when described from different localities. In conse-
quence, some of the information published prior to the 1960's on
these diseases is unreliable. The objectives of the current in-
vestigation are to survey the Caribbean region and determine the
localization, particularly, of LY and HR diseases. In addition,
alternative methods of diagnosis are being studied. During the
course of this work, observations have also been made on other
problems of coconut palm. This paper summarizes information
on the symptomatology and localization of systemic and lethal
diseases of coconut palm in the Caribbean region.

Symptomatology and Diagnosis
Lethal Yellowing
 The common cultivar of the Caribbean region, 'Jamaica Tall',
is particularly susceptible to LY disease. Symptoms usually begin
with the abortion of all developing fruit. Fallen immature nuts
usually have a dark water-soaked discoloration at the stem end.
Following, or occasionally preceding nutfall, a necrosis of
developing inflorescences occurs. Necrotic inflorescences are dark
brown in color and the male flowers remain attached. Fruit do
not develop on these inflorescences. Occasionally, a single yellow
leaf may occur in mid-crown at the time of nutfall and in-
florescence necrosis. However, systemic foliar yellowing usually
does not begin until four to eight weeks after initial symptoms.
This systemic yellowing begins in the oldest or lower leaves and
extends upwards through the crown over approximately an eight


212


week period. Necrotic leaves abcise cleanly from the trunk. Col-
lapse of the spear leaf usually occurs at about midway through the
foliar yellowing cycle. The necrosis affecting the spear leaf then
extends downwards into the meristem, which succumbs to a
putrid, foul smelling decay. The entire LY syndrome develops
over a three to five month period and ends with a dead telephone
pole-like trunk.
 Electron micrography of bud, inflorescence, root, and flag leaf
material from LY diseased coconut palms has consistently re-
vealed the presence of mycoplasma-like organisms (MLO) within
sieve tubes (Plavsic-Banjac et al., 1972; Thomas, 1979). The MLO
are extremely small, cell wall-less bacteria of variable morphology
(McCoy, 1984). LY has been demonstrated to be transmitted by
the planthopper Myndus crudus in Florida (Howard and Thomas,
1980).
 Diagnosis of lethal yellowing has thus far been restricted to
symptomatology with confirmation by electron microscopy. A
new approach using the DNA-specific fluorochrome DAPI
(Seemueller, 1976) is being investigated and shows considerable
promise as a rapid alternative to electron microscopy.

Hartrot
 Symptomatically, HR is very similar to LY in coconut palm.
Both diseases are characterized by nutfall, inflorescence necrosis,
foliar death, and a putrid rot of the growing point. However, HR
characteristically has a more rapid decline. Affected palms usually
die within two months of the onset of symptoms. Also HR tends
to produce a rapid browning of affected leaves rather than the
spectacular yellowing of LY. In addition, HR affected leaves tend
to break along the midrib. Extensive root necrosis is characteristic
of both diseases.
 Diagnosis ofHR is best made by light or electron microscopy of
root, inflorescence, or meristem tissues. Plant juice squeezed
from infected tissues and observed immediately by phase contrast
illumination at 400X in a light microscope will reveal the
presence of numerous Phytomonas staheli, flagellated protozoa
of the family Trypanosomatidae. Electron microscopy has re-
vealed that P. staheli, like the LY MLO, is also limited to sieve
tubes of the phloem (Parthasarathy et al., 1976; Waters, 1978;

 PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY-VOL. XX