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Title: First report of European pear rust (pear trellis rust) caused by Gymnosporangium sabinae on ornamental pear (Pyrus calleryana) in Virginia

Author
item HANSEN, MARY - Virginia Tech
item BUSH, ELIZABETH - Virginia Tech
item YODER, KEITH - Virginia Tech
item SUTPHIN, MARK - Virginia Tech
item Demers, Jill
item Castlebury, Lisa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2016
Publication Date: 7/13/2016
Citation: Hansen, M.A., Demers, J., Sutphin, M., Yoder, K., Bush, E., Castlebury, L. 2016. First report of European pear rust (pear trellis rust) caused by Gymnosporangium sabinae on ornamental pear (Pyrus calleryana) in Virginia. Plant Disease. 100(10):2166. doi: 10.1094/PDIS-03-16-0396-PDN.

Interpretive Summary: Fungi are a large and diverse group of organisms that cause serious diseases of crop and forest plants. Knowledge of the host range and geographic distribution of disease-causing fungi is critical for managing the movement of these destructive organisms. Recently a rust fungus was found on European pear trees, a popular ornamental and fruit tree in Virginia. This rust was identified using both morphological and molecular characteristics and determined to be a species not previously found in Virginia. This fungus is also capable of infecting eastern red cedar although it has not yet been found on this host in Virginia. Using these data plant pathologists will be able to monitor and control this disease and plant quarantine officials may be able to prevent the spread of this fungus onto other hosts or into other parts of the United States.

Technical Abstract: In November 2014, leaves of ornamental pear (Pyrus calleryana, cultivar unknown) with bright orange to reddish spots typical of infection by a rust fungus were submitted to the Virginia Tech Plant Disease Clinic from a landscape in Frederick County, VA, for diagnosis. Brown aecia with bulbous bases resembling acorns, characteristic of European pear rust (pear trellis rust) caused by Gymnosporangium sabinae, were present on the lower leaf surface (Kern 1973). Two ornamental pear trees in the landscape were heavily infected and scattered leaf lesions were observed on other ornamental pear trees in the neighborhood. Samples of infected leaves were sent to the USDA ARS Systematic Mycology & Microbiology Lab to confirm the presence of G. sabinae and for deposit in the U. S. National Fungus Collections (BPI 893287). Morphological characters were consistent with G. sabinae. Aecia were hypophyllous, in necrotic spots, roestelioid, 2 -5 mm high, balanoid, splitting along sides with apex intact; peridial cells sub-hyaline, verrucose to spinulose, elongated, 58 -119 um × 10 -22 µm; aeciospores light brown to yellowish-brown, minutely verrucose, globose to ovoid, 22 -29 um × 26 -35 µm, with walls 3 -5 µm thick. The ITS2 and 5' end of the 28S rDNA regions were amplified and sequenced using the primers Rust2inv and LR6 (Aime 2006) (GenBank KU593568). Sequences were 99 - 100% identical to G. sabinae sequences in GenBank. G. sabinae can infect leaves, fruit and young twigs and causes serious disease on ornamental pear and European pear (Pyrus communis). The alternate hosts of G. sabinae are in Juniperus section Sabina, but although a Juniperus species was present in the neighborhood, no signs of rust disease or cankers were found on any of the junipers. It has been reported elsewhere in the United States (CA, CT, MI, NY) and in Canada (BC); however, it has not previously been reported in Virginia. A report from Alabama could not be confirmed. Although European pear is not widely grown commercially in Virginia, it is grown as a backyard fruit tree, and ornamental pear is common in the landscape. G. sabinae can overwinter on both its pear and juniper hosts, increasing its potential for spread. This is the first report of European pear rust on ornamental pear in Virginia. Because eastern red cedar (J. virginiana) is susceptible and commonly present and invasive volunteer seeding of ornamental pears occurs within the region, we expect the rust fungus to spread to commercial and backyard European pears, especially in the Shenandoah Valley. As this rust can cause severe defoliation and dieback of pears, awareness of the presence of this disease is critical to its management on both ornamental and fruit-producing pears.