See:
Pear (Pyrus spp.) - Fire Blight
Note: Bradford pear (P. calleryana) is moderately susceptible to fire blight and has a weak branching characteristic. Newer cultivars with similar susceptibility include Capital and Cleveland Select. Cultivars Aristocrat, Autumn Blaze, Early Red, and Redspire are the least resistant types (but have stronger branching than Bradford). The most resistant cultivars include Chanticleer, Trinity, and Whitehouse.