A BACTERIAL LEAFSPOT OF TOBACCO 1 
By James Johnson 
Associate Professor of Horticulture , University of Wisconsin, and Agent , 
Office of Tobacco Investigations , Bureau of Plant Industry , United States 
Department of A griculture 
INTRODUCTION 
During the past five years a bacterial leafspot of tobacco occuring in 
Wisconsin has been the subject of investigation together with observa¬ 
tions on tobacco leafspots in general in various tobacco districts of the 
United States. The tobacco leaf is subject to an exceptionally large 
number of diseases, originating from a variety of causes, in some cases 
with distinctive and constant symptoms, but more often confusing when 
any determination or classification based on symptoms is attempted. 
This confusion is in some respects magnified by the fragmentary early 
literature and is due largely to common names having been applied 
without adequate consideration as to the causal agents of the diseases. 
Recently two or three leaf diseases have been described, however, in 
sufficient detail to permit of definite reference. It is the purpose of this 
paper to contribute to the knowledge of one other such disease. 
CAUSE 
This disease, which is not believed to be new to tobacco growers in 
Wisconsin, has been found to be due to a bacterial organism apparently 
previously undescribed. The causal organism has been named Bacterium 
melleum, n. sp., and a description of the organism and the symptoms of 
the disease it causes is given in this paper. 
COMMON NAMES 
The leafspot to be described here is ordinarily called “rust” by Wis¬ 
consin tobacco growers. This name, which is not a good one from a 
phytopathological standpoint, is in fact in use throughout most of the 
tobacco districts of the world, for a variety of leaf diseases of tobacco, 
and is, therefore, a very unreliable term. The term “rust” is frequently 
limited by the use of such combinations as “red,” “brown,” “white,” 
and “black rust;” but these again are of little significance when applied 
by different individuals and have little definite relation to the causal, 
agent concerned. Other terms such as “firing,” “black fire,” field fire,” 
“wildfire,” “speck,” and “frogeye” are terms which have been com¬ 
monly used as synonymous with “rust,” though the term “frogeye” 
is now generally limited to the disease caused by Cercospora nicotianae 
1 Accepted for publication May io, 192a. Cooperative investigations of the office of Tobacco Investiga¬ 
tions, Bureau of Plant Industry, United States Department of Agriculture, and the Wisconsin Agricultural 
Experiment Station. 
(481) 
Journal of Agricultural Research, 
Washington, D. C. 
adg 
Vol. XXIII, No. 6 
Feb. 10, 1923 
Key No. G-280 
