Phytoplasma in Various Palm Species & Other Genera
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When LY invaded southern Florida, where a wide array
of palm species are grown as ornamentals, it became apparent that
many palms additional to coconut palm are susceptible. One of these
is the date palm, Phoenix dactylifera.
The date palm
is native to arid (BW) regions, and the climate of southern Florida
is classified as between Aw and As, i.e., humid tropical (Koeppen
system). Therefore, date palms are not grown extensively, and there
were never enough individuals in this area to judge their degree of
susceptibility. But among the relatively few individuals, there was a
high loss due to LY. Therefore, P.dactylifera was
tentatively rated as 'highly susceptible'.
The Canary
Islands date palm (Phoenix canariensis) is more common in
thearea. It, too, was found to be susceptible. But palms that are
referred to as Canary Islands date palms in Florida are very often
hybrids between P. dactylifera and P.
canariensis.
Based on these observations, P.
dactylifera is more susceptible to LY than P. canariensis,
and the P. canariensis that contract LY are quite often
hybrids with P. dactylifera. Pure canariensis seems
to be less susceptible.
Within a few years after its discovery
in the Miami area, LY had spread north to the city of Stuart, so that
it was present all along the southeast coast. But it made no further
progress north. Since P. canariensis is grown throughout the
Florida (it is relatively cold-hardy; coconut palm doesn't grow north
of Stuart), some observers thought that it would continue its course
northward on P. canariensis. But it has never spread beyond
the range of coconut palm in Florida!
In the early 1980s, a
disease of Phoenix palms (mostly canariensis, but
some dactylifera) that had all of the symptoms and
destructiveness of LY began spreading in southern Texas. Randy McCoy,
who was one of the plant pathologists at Fort Lauderdale at the time,
went to Texas and took bud samples and brought them back to Florida
for EM examination. Within a few days he found MLO's in these
samples, thus the disease was diagnosed as LY.
This seemed
ominous for Florida, because it was the first evidence that LY could
spread in an area where coconut palms don't grow. Southern Texas
doesn't have a tropical climate.
Some surveys were conducted
to identify potential vectors of the disease in Texas. Myndus
crudus was found, but in very small numbers, and there were
some other cixiids.
In light of the more recent knowledge of
the different phytoplasmas associated with LY-like diseases, it may
be questioned whether the Texas 'LY' was caused by a phytoplama
identical to that associated with Caribbean and Florida LY. It acted
differently (it was the only case in which this kind of disease has
occurred in the absence of coconut palm, and it was a disease largely
of P. canariensis which in Florida is not highly susceptible
to LY). It would be interesting to compare these diseases using the
new molecular technology.
However, this can't be done. A
severe frost hit southern Texas in 1989 and eliminated so many of the
remaining Phoenix palms that it also eliminated the
disease!
(From information supplied by Bill
Howard)
A disease that is killing mature Phoenix canariensis (Canary Island date palm) in Corpus Christi, Texas brought to the attention of Nigel Harrison by Michael Womack (Texas Agricultural Extension Service) and Richard Maxwell (Tree Saver), closely resembles the desciption of a lethal decline of Phoenix palms that occurred in Brownsville, Texas during the late 1970s (McCoy et al.1980. Plant Dis. 64: 1038-1040) which in turn was considered to be lethal yellowing. Phytoplasmas have been detected in all 11 symptomatic test palms using a phytoplasma- specific PCR assay. The Phoenix decline phytoplasma is related to, but can be differentiated from, the lethal yellowing agent.
(From information supplied by Nigel Harrison).
Also see Lethal Yellowing Disease Symptoms on (Date) Palm
There have been two reports of phytoplasma associated with date palm in Sudan. See First report of a phytoplasma associated with a disease of Date palms in North Africa and Slow Decline a New Disease of Mature Date palms in North Africa associated with a phytoplasma
Mycoplasmalike bodies were associated with phloem degeneration in declining Pandanus in Florida (Thomas & Donselman, 1979) and phytoplasma were subsequently confirmed by RFLP analysis (Harrison & Oropeza, 1997).
The palm-like monocot, Palma Jipi, was seen to have annual losses estimated at 10% from a lethal decline first reported at Kalkini, Campeche, México in 1994, an area where LY of coconut was also prevalent. Affected plants die within a few weeks of primary symptoms, a progressive yellowing of successively younger leaves (Cordova et al, 2000). Inflorescence or fruit symptoms where not mentioned in this report.
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