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CICLY · Lethal Yellowing Disease of Coconut Palm

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Susceptibility and resistance of palms to LY   Message List  
Reply | Forward | Delete Message #2158 of 2180 |
Greetings LY researchers and other colleagues,

During the LY epidemic in Florida, the University of Florida and the
Division of Plant Industry (DPI) of the Florida Department of Agriculture
and Consumer Services worked together in maintaining a list of palm species
that were susceptible to LY. Basically the way this worked was that DPI
inspectors, who perform nursery inspections and also inspections and surveys
in the general urban landscape, would perform field diagnoses of LY in hosts
that had not been reported previously. Then Darryl Thomas, a plant
pathologist with the University of Florida, would confirm these diagnoses by
EM examination of bud tissue from the field-diagnosed palms for presence of
phytoplamas. This effort has continued to this day, with Nigel Harrison
confirming diagnoses by molecular analysis.

A few to several palm species would be added each year to the list. The list
of susceptible palms now stands at 38 (the last time I heard, which was
fairly recently).

Knowing the species that contract LY is one thing. It is also helpful to
know the relative susceptibility of different species. Those of us who were
conducting research on LY during the mentioned Florida epidemic learned by
observations on many affected sites that the incidence of LY was
consistently higher on certain species than others, and some species never
contracted the disease. For example, Pritchardia species frequently
contracted LY, and thus we considered them to be highly susceptible. In
contrast, none of us ever saw a case of LY in cabbage palmettos (Sabal
palmetto), so we rated that species as probably not susceptible to LY

In addition to this data on apparent degree of susceptibility of different
species collected by roaming around and looking at what was going on in the
general landscape, data from a well-designed disease trial garden would be
very interesting. Of course, it takes time for a trial garden to grow and be
useful in testing susceptibility to a given disease, so it would have been
necessary for a trial garden to have been planted on the Florida mainland
years prior to, but in anticipation of, the invasion of the mainland by LY.
It is unlikely that anyone would have thought of this, especially since
prior to the LY epidemic in Florida it was not known that this disease
attacked palms additional to coconut.

But the next best thing to a trial garden was Fairchild Tropical Botanic
Garden (the term 'Botanic' has been added recently to the name). It was a
sad thing that LY invaded that beautiful and scientifically useful living
collection of palms and other tropical plants, but it was also an
opportunity to find out a little more about the susceptibility of different
palm species.

We therefore worked with Marry Collins, a horticulturist at FTBG, in
compiling data on the apparent susceptibility of different palms in the

The data have their limitations, because for one thing FTBG had not been
designed to test palms against a disease. It was designed to display palms,
sometimes of different ages, in different settings. Rainforest palms were in
a different area than palms native to savannas, etc. A well-designed trial
garden would have each species represented by palms of the same age, all
species replicated with equal numbers of palms, etc. In spite of these
limitations, we found that the relative susceptibility indicated by these
observations did match pretty well with what we saw in southern Florida in
general during the LY epidemic.

We summarized these observation in an article published in the FAO Plant
Protection Bulletin {Howard, 1978 #280}. The complete list of species, which
shows the total number all of the palm species at that time in FTBG, and the
number of each species that contracted LY (the number was 0 in all but a
small percentage of species) was too long to publish in a bulletin like
this, so we published it as a Fort Lauderdale Agricultural Research Center
Report, and mailed copies to interested persons.

The report is probably still of some potential use for LY researchers, so
recently I looked into how we could distribute it to interested parties. As
a result, the report is now on our website.

You can see (and print) the report using the following steps:

Go to the following Internet site:


This is the website of the Fort Lauderdale Research & Education Center

On the left hand side, you will see a list of topics. One is Palm Production
and Maintenance.

Under that title is a subtitle: Palm diseases. Click on it.

You will now see a listing of articles on palm diseases.

The report is listed there with the title PALM SPECIES SUSCEPTIBLE AND

(Note: MLO-Associated lethal declines is the name we used to give to what we
thought was LY, but in palms other than coconut. Nowadays, we say
phytoplasma instead of mycoplasmalike organisms, and we consider the
so-called declines in the non-coconut palms to be the same thing as LY.)

Best wishes,

F. W. Howard, Ph.D.
Associate Professor of Entomology
University of Florida, IFAS
Fort Lauderdale Research & Education Center
3205 College Avenue
Fort Lauderdale, Florida 33314


Mon Aug 20, 2007 7:24 pm

"Forrest W. Howard" <fwhoward@ufl.edu>
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Greetings LY researchers and other colleagues, During the LY epidemic in Florida, the University of Florida and the Division of Plant Industry (DPI) of the...
Forrest W. Howard
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Aug 21, 2007
5:32 pm

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