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Title: First report of Gymnosporangium sabinae, European pear rust, on Bradford pear in Michigan

Author
item YUN, HYE YOUNG - Seoul National University
item Rossman, Amy
item BYRNE, JAN - Michigan State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2009
Publication Date: 8/1/2009
Citation: Yun, H., Rossman, A.Y., Byrne, J. 2009. First report of Gymnosporangium sabinae, European pear rust, on Bradford pear in Michigan. Plant Disease. 93(8):841.

Interpretive Summary: Rust fungi are a very large and diverse group of parasites that attack crop and forest plants. Accurate knowledge of the distribution of rusts is important for tracking the movement of these disease-causing fungi. In this research a rust fungus that infects pears and other related plants was discovered for the first time in Michigan. The rust was observed on leaves of Bradford pear trees. This rust species is known primarily from Europe, although it has been accidentally introduced into California and British Columbia. Knowledge of the distribution of plant pathogenic fungi is useful to agronomists and plant pathologists as well as plant regulatory and quarantine officials.

Technical Abstract: Bradford pear, Pyrus calleryana Decne., is well known as an ornamental plant for its flowers, leaf color in fall, and disease resistance, making it desirable as a street tree. In August and October 2008, the aecial stage of Gymnosporangium sabinae (Dicks.) G. Winter was collected on leaves of P. calleryana in Michigan, Oakland Co., Farmington. Using published descriptions of G. sabinae as the synonym G. fuscum (1-4), the Michigan specimen was identified and confirmed by comparison with previously reported European and U.S.A. specimens (BPI 118736, BPI 856578). The diagnostic characteristics of G. sabinae include: spermagonia epiphyllous; aecia hypophyllous, roestelioid, 3-6 mm high; peridium balanoid (acorn-shaped), becoming elongated at maturity, pale yellow, sides opening with lateral slits but remaining attached at light brown, pointed apex; peridial cells elongated, 51–68 µm long, outer walls smooth, inner walls and side walls sparsely echinulate; aeciospores globose to broadly ellipsoid, somewhat angular, surface slightly coronate, 22–32 × 22–36 µm, walls orange, 3.5–5.5 µm thick. Telia and teliospores of G. sabinae are produced on the alternate host, various species of Juniperus sect. Sabinae, but were not observed in Michigan. The specimen from Michigan is deposited in the U.S. National Fungus Collections (BPI 878928). Gymnosporangium sabinae is widely distributed in Europe extending to Asia and North Africa but is rarely reported in North America. It was accidentally introduced into California in the aecial stage on Pyrus communis L. and telial stage on Juniperus chinensis (2) as well as Canada (British Columbia) (3, 4). The only previous report of G. sabinae on Pyrus calleryana is in Germany (1). Gymnosporangium sabinae is known to attack commercial pears and ornamental juniper plants in Europe. This species is distinguished from other species of Gymnosporangium on Pyrus by the balanoid (acorn-shaped) peridium.