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First report of tomato
yellow leaf curl virus (TYLCV) in Arizona
A new plant virus identified in fall
2006 in Arizona threatens not only home gardens, but also the
commercial tomato industry in the state. Tomato yellow leaf curl
virus, also known as TYLCV, was found in 2 home gardens in the
Phoenix area.
Tomato plants infected by the TYLCV
develop severely curled, yellowing leaves, shattered nodes, and
short stalks. The virus causes many of the flowers to abort,
lowering fruit set and reducing yields. Symptoms are most
apparent on the growing tips of plants, where the newest growth
is taking place.
"You'll see very small, stunted plants
that aren't going to be able to produce fruit -- not good enough
for shipping and storage," says Judith Brown, a virologist and
whitefly vector biologist in the department of plant sciences at
the University of Arizona. "The virus stresses the plants beyond
belief, and they simply stop growing."
Brown isolated DNA and identified the
virus from plant samples submitted by Mary Ann Garewal, a
UA-certified master gardener in Surprise, who observed symptoms
and collected samples from her vegetable garden and those of
another Phoenix gardener. At about the same time, Brown also
identified a distinctly different isolate of the virus on
infected commercial tomato plant samples from Sonora, Mexico,
suggesting that the 2 isolates came from different sources.
The plant samples from both Arizona
(USA) and Mexico were also infested with the "B" biotype of the
sweet potato whitefly, _Bemicia tabaci_, which feeds on the
leaves and can transmit the virus to other plants through its
saliva.
TYLCV 1st infected tomatoes in the
western hemisphere in the Caribbean and along the eastern coasts
of both the United States and Mexico in the early 90s. "It
seemed to be contained in those areas until it was introduced in
Texas last summer," Brown says. The source of that outbreak was
traced to infected commercial transplants that were possibly
infected by the virus in plants brought in from out of state.
TYLCV has also been tracked from the
east coast states of Mexico to the Pacific coast production area
in the state of Sinaloa, where the virus ravaged commercial
tomato crops throughout the state during spring 2005 and again
in fall and spring 2006, according to Brown. "In the summer of
2006 we next found it in Sonora," she says. "Now it's becoming a
giant epidemic across the Pacific coastal Mexican states,
causing heavy yield losses in fresh-market tomatoes and peppers
that are exported to the United States."
Brown notes that the TYLCV identified in
Arizona did not come from Mexico.
DNA testing matches it with isolates
from Texas. When viruses pass through different hosts,
particularly ornamentals or new hosts, they can mutate into
different isolates and then be introduced back into a crop.
"It's a very prolific virus," Brown says. "If TYLCV infects a
variety of tomato that is not resistant, you'll have a huge
problem. I don't think any of the varieties grown hydroponically
in greenhouses are resistant, although some of the field
processing varieties are. None of the current home garden
varieties are resistant."
TYLCV infects not only tomatoes, but
also beans and peppers in home gardens, and some ornamentals.
Brown advises against spraying
whiteflies to control the virus because by the time the symptoms
appear it is too late to stop the disease. She adds that there
are currently no chemical or biological controls for TYLCV. "The
best approach is to avoid introducing the virus in transplants.
Virus-free seedlings are the way to go," she says. "You're
safest if you buy virus-free plants or start your own from seed
-- although that still may not help if your garden or crop is
near an infected field or a neighbor's garden that harbors the
virus."
For more information, contact Judith K
Brown, at 520-621-1402, <jbrown@ag.arizona.edu>.
[byline: Susan McGinley]
