Abstract
The epidemiology and etiology of a disease of Fraxinus velutina (Arizona or velvet ash) called ash decline was investigated. Symptoms of ash decline include a progressive dieback of stems and branches as well as yellowing and necrosis of leaf tissue. The incidence and severity of ash decline in F. velutina cv. Modesto trees in the Phoenix, Arizona, U.S., metropolitan area was studied over an 8-year period. Symptom severity increased dramatically during this time period with a 30% mortality rate of trees in the study group. Etiological studies determined that phytoplasmas were associated with ash trees showing ash decline symptoms. Phytoplasmas were detected in the phloem sieve tube elements of plants using the DAPI microscopic test, and phytoplasma DNA was detected in ash tissue using a polymerase chain reaction (PCR) assay. The relationship of the phytoplasmas associated with ash decline to the ash yellows (AshY) phytoplasmas is discussed.
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