Host range and distribution of the phytoplasma causing Arizona ash decline

Abstract

Ash decline (AD), caused by a phytoplasma, is a progressive dieback disease previously reported in Fraxinus velutina. The host range and distribution of AD is discussed based on samples collected from ash trees sampled from across the state of Arizona, U.S., including both wild-type F. velutina in riparian areas and F. velutina cv. Modesto, F. velutina cv. Rio Grande, and F. uhdei in landscaped areas. The results of the statewide survey indicate that AD is found in native and cultivated ash trees, with F. velutina cv. Modesto exhibiting the highest (100%) level of disease in the Phoenix metropolitan area. Wild-type F. velutina and F. velutina cv. Rio Grande also exhibited AD symptoms but with lower frequency and severity. Fraxinus uhdei did not exhibit symptoms of AD. Phytoplasma infection was detected in all tree types of F. velutina trees using DAPI staining and polymerase chain reaction (PCR) but was not detected in F. uhdei. Higher frequency of phytoplasma infection was detected in tree canopies versus roots in contrast to previous results reported in white ash. PCR was found to be more efficient at detecting the low-titer infection levels typical of F. velutina in comparison to DAPI staining. © 2005 International Society of Arboriculture.