Agrobacterium tumefaciens
When first discovered, there was worry among nursery owners and growers. It is now thought that the disease is caused by "Agrobacterium tumefaciens". Researchers have been working to isolate the bacteria, and also have asked for help from nurseries and growers in looking for links to possible causes. At least 15 states, along with Canada and the U.K. have reported cases of tissue proliferation (Zimmerman, 1997).