The following is information about a rust disease attacking Callery pears in Delaware.
Samples of 'Bradford' Callery pear fruit and 'Redspire' have been diagnosed with cedar-quince rust. Since pear is in the same family as hawthorn and serviceberry--usual hosts of this rust, it stands to reason that pears could be infected as well. But, pear is a new host for this common disease. Infected fruit have the elongated white tube structures that protrude and turn orange with time. It is a superficial disease that only infects the fruit. So only the appearance of plants are affected not overall health. Since Bradford pears don't set lots of fruit anyway it may be hard to spot infected ones. Since there is concern over Bradford pears setting fruit and escaping into the landscape it will be interesting to learn if infected fruit can produce normal seed and germinate.
Information from Bob Mulrooney, Extension Plant Pathologist, UD