492 
Journal of Agricultural Research voi. xxm, No. 6 
SUMMARY 
A bacterial leafspot disease of tobacco has been under observation 
and study in Wisconsin for five years. This disease is one of three or 
more different leaf spots of tobacco commonly grouped under the common 
name “rust” by the growers in Wisconsin. The other “ rust ” spots 
appear to be nonparasitic in nature. 
This disease has not been especially serious in recent years, but it is 
believed that it is the “rust” which has been most serious in past years 
and may become so again at any time that the required favorable con¬ 
ditions for its occurrence appear. 
The Wisconsin leafspot of tobacco differs from both the wildfire 
leafspot and the angular leafspot occurring in other sections of the 
United States, and from the black rust occurring in Sumatra, all of which 
are bacterial in nature. The symptoms of the wildfire disease and of 
the Wisconsin leafspot, however, are much the same. 
The disease usually manifests itself by round, brown, or rust-colored 
spots, usually less than % inch in diameter, but frequently running 
together to form larger irregular lesions. Frequently the young lesions 
are marked by a distinct chlorotic area or halo surrounding the point of 
infection. Under field conditions infection usually starts on or is con¬ 
fined to the lower leaves. Lesions may also occur on young leaves in 
the seed beds. 
The disease is caused by a yellow bacterial organism apparently pre¬ 
viously undescribed. The name Bacterium melleum f n. sp., is suggested, 
and the more common morphological and cultural characteristics are 
given. 
Artificial infection has been secured only through wounding by needle 
pricks. Under the conditions of the inoculation experiments in the 
greenhouse this has also been more or less true with the wildfire organism, 
which has been studied comparatively in practically all of the work done 
with the Wisconsin leafspot organism. Under field conditions it is not 
believed that wounding is necessary for infection. Temperature and 
humidity conditions in themselves do not apparently govern the occurrence 
of infection. Some data secured indicate that predisposition may be 
influenced by the fertilizing materials available. 
It is believed that the disease ordinarily starts in the seed beds, from 
which it is transferred to the field. Growers are advised, therefore, not 
to use plants from infected seed bed areas for transplanting. 
literature CITED 
(1) Delacroix, Georges. 
1905. LA ROUILLE BLANCHE DU TABAC ET LA NIELLE OU MALADIE DE LA 
MOSAiQUE. In Cojnpt. Rend. Acad. Sci. [Paris], t. 140, p. 678-680. 
(2) Elliott, Charlotte. t 
1920. halo-blight or oats. In Jour. Agr. Research, v. 19, p. 139-172, pi. 
C (col.), pi. 26-35. Literature cited, p. 172. 
(3) FrommE, F. D., ana Murray, T. J. 
1919. ANGULAR-LEAFSPOT OF TOBACCO, AN UNDESCRIBED BACTERIAL DISEASE. 
In Jour. Agr. Research, v. 16, p. 219-228, pi. 25-27. Literature cited, 
p. 227-228. 
(4) Honing, J. A. 
1914. DE “ZWARTE ROEST m DER DELI-TAB AK. (THE BLACK RUST OF DELI 
tobacco.) Bul. Deli Proefstat. Medan, no. 1, 16 p., 2 pi. English 
resum£, p. 10-14. Literatuur, p. 15-16. 
