See:
Lilac (Syringa spp.) - Bacterial Blights
Diseases Caused by Pseudomonas syringae
Note: Shoot tip dieback is a common symptom where Pseudomonas syringae is isolated. Other plants affected include aspen, blueberry, dogwood, hazelnut, lilac, magnolia, maple, and oriental pear. Some nurseries have linden trees with severe symptoms while others have not seen the problem.