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Dr. Mike Stanghellini at the University of California, Riverside and colleagues
have reported the identification of a new disease on watermelon plants in the Coachella
Valley of California. Symptoms on foliage include yellowing, wilting, and death
of leaves, beginning at the crown and rapidly making progress towards the tips of
vines. The large main roots look healthy but the small feeder roots display a brownish
discoloration. This disease resulted in collapse of mature watermelon plants at
first harvest and was found in several drip-irrigated fields. A fungus was recovered
from the discolored feeder root tissue and experimentally shown to cause symptoms
observed in the field. The fungal pathogen, called Olpidium bornovanus, has not
until now been known to cause disease on watermelon plants anywhere in the world.
This fungal pathogen produces motile zoospores as part of its life cycle. Zoospore
production, movement, and disease development are enhanced by wet soil conditions.
Soil in affected fields apparently was nearly saturated due to daily application
of irrigation water through drip-tape. Does this disease occur in Arizona? At this
time, we do not know. If watermelon plants with the foliar and feeder root symptoms
described above are found in Arizona watermelon plantings, especially in drip-irrigated
fields with wet soil, please bring the root system of affected plants, including
the small discolored feeder roots, to the University of Arizona Yuma Agricultural
Center for analysis.
Patogenia de Olpidium bornovanus en sandía, Gomez, Tello, 11/12, Universidad Almeria
España.
To contact Mike Matheron go to: matheron@ag.arizona.edu.
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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
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