I suspect you may have run into complications with the photos. It would be nice to see them, but with the additional information you provided in your reply, I think I can answer your question without the pictures. I can hardly believe a nursery told you the problem might be "just" root rot. That must not have been a very well-informed employee. Root rot is extremely serious and often fatal. But symptoms of root rot include yellowing leaves that fall prematurely, slowed growth, branch dieback, and thinning of the tree's crown. These symptoms occur because the rotted roots cannot transport nutrients and water up the trunk. If all the roots are affected, the tree will die. If parts of them are affected, the corresponding above ground sections will be sickly. Over a period of years, such a tree will continue to decline. From what you have describe, I don't believe your tree has root rot.
The symptoms you outlined are classic for fire blight: the wilting of the blossoms and the way they stayed on the tree, the canker, the wilted leaves, and the dead tips. There is no cure for fire blight. Fungicides can prevent it, but once it affects a tree the way it has yours, the fungicides won't help. Fire blight occurs most often in years with warm rainy springs. The fungicide sprays have to begin before any symptoms occur.
Sometimes a tree with fire blight can be saved. Pruning is the first step. You need to prune off all affected areas. It's best to go about 12 inches below where the visible damage has occurred. After each cut, you must sterilize your pruning tools by dipping in bleach or using a household disinfectant. Otherwise the blight can be spread by them. The pruning should be done in the winter.
Check in the spring to see if the tree appears alive. If it does, begin a spray program.
A copper fungicide can be applied before bud break (it can damage the buds if applied too late). Then the bactericide aluminum tris can be used during bloom. Blight Ban is a biological produce produced to control blight, but it is only available to commercial applicators. If you want the best chance of saving the tree, it would be best to consult a certified arborist. An arborist could also tell you the chances that the tree can be saved, and if so, the chances that its beauty could be preserved. This link will take you to a directory of arborists:http://www.isa-arbor.com/faca/findArborist.aspx
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