Evaluating Fire Blight Resistance among Flowering Crabapples (Malus spp.) and Pears (Pyrus spp.)

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Andrew C. Bell1, Thomas G. Ranney1, Thomas A. Eaker1, and Turner B. Sutton2

1Department of Horticultural Science, Mountain Horticultural Crops Research and Extension Center, North Carolina State University, 455 Research Drive, Mills River, NC 28759
2Department of Plant Pathology, North Carolina State University, 1320 Varsity Drive, Raleigh, NC 27695-7643

A paper from the Proceedings of the 11th Metropolitan Tree Improvement Alliance (METRIA) Conference held in Gresham, Oregon, August 23-24, 2000, and cosponsored by the Landscape Plant Development Center.

Introduction

Fire blight, caused by the bacterium Erwinia amylovora, is one of the most significant diseases of rosaceous plants, particularly those members in the subfamily Maloideae. Susceptible plants, including taxa of flowering pears and crabapples, can be severely damaged and killed by fire blight in both nursery and landscape plantings. This disease can be especially problematic in both the eastern and mid-western regions of the United States where environmental conditions are favorable for the pathogen. Although many taxa are susceptible to fire blight, flowering pears and crabapples vary considerably in resistance to this disease providing opportunities for the selection and development of superior plants (Benson et al.,1991; Windham et al., 1997)

Research on fire blight resistance among flowering pears and crabapples has been limited and has primarily been based on observations of natural infection (Benson et al., 1991; Green, 1986; Nichols, 1983, 1986; Windham et al., 1997). Because the incidence of fire blight can be sporadic and vary from region-to-region and year-to-year, observations and results from field surveys can be inconsistent and highly variable. Plants that initially appear to be resistant may later be found to be susceptible when conditions are favorable for pathogen development. Controlled inoculations of actively growing shoots with E. amylovora can provide an effective and consistent means for evaluating fire blight resistance (Aldwinckle and Preczewski, 1979; Bonn and Elfving, 1990).

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