Feb. io, 1923 
A Bacterial Leaf spot of Tobacco 
483 
Wolf and Foster (7) in 1917 described the wildfire disease as it occurred 
in North Carolina and Virginia, following an unusually severe outbreak 
and proved the causal organism to be a bacterium, which they named 
Bacterium tabacum. This disease apparently has since spread to most of 
the other tobacco districts in the United States, seemingly from the North 
Carolina epidemic of 1917 as a center of infection. This disease is not 
readily distinguished from the Wisconsin leafspot in general symptoms, 
although the chlorotic area around the point of infection is usually larger 
and more common than in the Wisconsin leafspot. The wildfire organism 
is also a much more vigorous parasite than the Wisconsin leafspot 
organism, and the disease may consequently be much more prevalent 
aid serious where it occurs. Fromme and Murray (j) investigated a 
leafspot disease in Virginia, which had apparently also existed for a 
considerable time in that State, and found it to be due to a bacterium 
which they named Bacterium angulatum. This disease has been named 
by them “angular leafspot" on account of the angular shape of the 
lesions. It cannot be readily confused with other bacterial leafspots 
but may be difficult to distinguish at times from certain nonparasitic 
spots when judged by symptoms alone. 
DESCRIPTION OF THE DISEASE 
The Wisconsin bacterial leafspot has been found ordinarily on the 
lower leaves of the plants in the field. Usually it is most marked on 
the lowest leaves but has been observed during this investigation up 
to the middle leaves. In severe outbreaks, not seen since the beginning 
of this study but earlier noted and referred to by others as “ old-fashioned 
rust, ” the leaves on the entire plant may be involved. That the disease 
may occur on young leaves is evidenced, however, by the observation 
of several infections in seed beds from which the causal organism has 
been isolated. The older leaves are seemingly more predisposed to a 
rapid collapse and death, and finally, browning of the tissue when once 
infected, but when artificially inoculated by needle punctures the top 
leaves show equal predisposition to infection, and the development of 
the chlorotic area surrounding the point of infection is even more marked 
than on lower leaves. The common occurrence of the disease on the 
lower leaves in the field is due quite likely to the more favorable environ¬ 
mental conditions offered there for infection and progress of the disease. 
The disease in the seed beds ordinarily is inconspicuous and not as 
typical as in the field. The spots are usually small and more angular 
than in the field and the chlorotic area less distinct (PI. 2, A). The old 
lesions are usually small and light-colored, but when they run together 
the young leaves present the appearance of being blighted. 
In the field the young spots are usually round, frequently with a 
small central fleck surrounded by a distinct chlorotic area or halo, iden¬ 
tical with that of the wildfire disease. Under other conditions this halo 
may not appear at all or may disappear rapidly, the tissue surrounding 
the point of infection collapsing and soon turning brown in color, in 
some cases possibly wdiite. Enlarging spots may or may not be limited 
by the veins of the leaf. At times the infected area seems to pass over 
the vein without injury to it. At other times, however, the parasite 
may enter the vein and follow it, producing an elongated lesion. The 
diameter of the spots may vary from 1 mm. to 1 cm. or more, frequently 
coalescing, and hence involving large areas of the leaf. The old lesions 
