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Two Lettuce Wilt Diseases Compared. Fusarium wilt of lettuce, caused by the fungus
Fusarium oxysporum, f. sp. lactucae, was first detected on lettuce in Arizona during
the 2001-02 growing season and continues to be found in lettuce fields from mid-October
through early January. There is another wilt disease of lettuce called Verticillium
wilt and caused by the fungus Verticillium dahliae. This disease has occurred in
the Salinas Valley since 1995 but has not yet been found in Arizona. The primary
symptoms of each disease are similar and consist of internal discoloration of the
root cortex and plant wilting followed by death. The internal root discoloration
ranges from green, brown to black in plants infected with Verticillium and reddish-brown
to black in plants infected with Fusarium. Since symptoms of both wilt diseases
are similar, true disease identity only can be achieved by bringing symptomatic
lettuce plants to The University of Arizona Yuma Agricultural Center, where the
causal pathogen can be isolated from infected root tissue and identified by microscopic
examination. Both wilt pathogens are soil inhabitants which can persist there formany
years. Both pathogens also can be seed-borne. The lettuce Fusarium pathogen can
only infect and cause disease on lettuce, although it may sustain itself on roots
of other plants without causing disease
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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