Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2010
Publication Date: 8/24/2010
Citation: Gregory, N., Bischoff, J., Dixon, L.J., Ciurlino, R. 2010. First report of the Telial stage of Japanese apple rust on Juniperus chinensis in North America and confirmation of the Aecial stage on Malus domestica. Plant Disease. 94:1169. Interpretive Summary: Apples and crabapples are important commercial fruit and ornamental trees and both are susceptible to rust diseases, which cause reduced fruit quality and production. Japanese apple rust spores produced on Chinese juniper are able to infect apples and cause disease. The Japanese apple rust pathogen was detected in Delaware on Chinese juniper for the first time following a report of this disease on ornamental crabapples in the same location in April 2009. Symptoms of the disease were described and DNA sequences were compared with samples from Asia where the rust fungus has been historically present to confirm the identification. It is likely that the disease is present in all areas where both plants are grown. This research will be used by plant pathologists who are developing strategies to track and control the disease caused by this rust fungus.
Technical Abstract: Following a report in April 2009 of the presence of Gymnosporangium yamadae on crabapple (Malus toringo Siebold) in Wilmington, Delaware (1), University of Delaware, State of Delaware, and USDA/APHIS PPQ personnel collaborated to confirm and document the pathogen. G. yamadae Miyabae ex G. Yamada is the causal agent of Japanese apple rust. The fungus is known from Asia with an aecial state on economically important Malus species and telial state on Juniperus chinensis. During the April 2009 site visit, ornamental J. chinensis were observed near the original crabapples. On May 7, 2009 telial galls were collected from the ornamental J. chinensis at the Wilmington site. The telia were confirmed by morphometric analysis and molecular data to be G. yamadae, the first report of the telial stage in North America. The rDNA large subunit (LSU) sequence derived from the collected telial galls (GU058012) was identical to the eight G. yamadae LSU sequences (FJ848760-FJ848765, FJ559373, FJ559375) reported from Korea by Yun et al. (2). Teliospores were 45-54µm long, with pedicels that were wide (7.0-8.4 µm) along the full length. In July of 2009, crabapple leaves with upper leaf spots and lower leaf aecia were collected, and identified as the aecial stage of G. yamadae on the basis of roestelioid aecia with long cornulated peridia that lacerate along the sides. The aecia differ from those of G. juniperi-virginianae, the causal agent of cedar apple rust, which has aecial peridia that fimbriate to the base and are strongly recurved (3). Leaves of M. domestica on the University of Delaware farm in Newark were confirmed to have Japanese apple rust on Aug 4, 2009, the first report on domestic apple in the United States. Following release of a USDA Pest Alert, subsequent samples submitted to USDA/APHIS PPQ indicated widespread incidence of the G. yamadae aecial state in the Northeast, including MD, ME, NH, NJ, NY, PA, and RI. Japanese apple rust likely went undetected for several years due to similarities to cedar apple rust. The G. yamadae telial gall collected from Wilmington, DE was deposited into the US National Fungus Collection (BPI 879273).