A number of plant pathologists have designated
T. J. Burrill, Professor at the University
of Illinois, as the scientist who first outlined
creditable proof that bacteria could cause plant
disease. Since this investigator presented his
evidence in 1878, before development of pure
culture methods and Kochs’ rules of proof, one
can justifiably ask what constitutes “evidence”
or “proof” that bacteria cause disease in plants.
How much evidence would be necessary to
establish cause and effect at such a time in
history? Who would have the authority to
make final judgment on the quality of the
proof?
Discovery is often determined by time and
circumstances. Fire blight disease of pear,
apple, and quince had been known since co