Feb. io, 1923 
A Bacterial Leaf spot of Tobacco 
485 
On his return to Wisconsin similar leafspots were noted, among them 
certain spots on a row of a southern type of tobacco in the experimental 
plots at Madison, though not occurring nearly as seriously as in the 
fields seen in North Carolina. The records show that two of the isola¬ 
tions from this row gave white organisms, one of which was infectious. 
Unfortunately this culture died before a detailed study could be made of 
it, so that we are not at all certain that it was the wildfire organism. 
The writer's earlier isolation from the seed bed leafspots and later isola¬ 
tions from the field yielded, however, only yellow infectious organisms. 
No white organism has since been isolated except following known 
cases of inoculation with the wildfire organism. It is felt that this 
explanation should be made here in view of a statement made by Wolf 
and Foster (7) as a result of correspondence, to the effect that wildfire 
occurred in Wisconsin in 1917. While the “similar spot" referred to 
has developed to be what we now call the “ Wisconsin leaf spot, ” there 
is still some probability that we did have one case of wildfire on a row of 
southern tobacco in 1917, and if so, it seems likely that it was the result 
of seed-borne infection. In any case wildfire can not be said to have 
occurred in Wisconsin in 1917 in the sense that it has since been reported 
from other States, nor was it introduced in that manner until 1922. 
During the last five years a large number of isolation tests have been 
made from various sorts of leafspots of tobacco. Wherever fairly fresh 
and young spots of the wildfire disease or the Wisconsin leafspot have 
been plated out, no difficulty has been encountered in getting pure cul¬ 
tures at once, so that the distinction between these two diseases has been 
readily established. The method employed has been simply to select a 
young lesion, cut it out with a scalpel, and rinse it through 8 to 10 sterile 
water blanks with vigorous shaking. It was then transferred to a tube 
of bouillon, mashed with a sterile scalpel or rod on the side of the tube, 
rinsed into the bouillon and allowed to stand 15 to 30 minutes. One to 
six loopfuls of the bouillon werethen transferred to melted potato agar 
at about 45 0 C. and plates poured. Cultures were usually kept in stock 
on potato-dextrose agar in the ice box. Twelve different isolations of 
the Wisconsin leafspot organisms have been made over a period of five 
years. Practically all the cultural character studies were made with one 
organism (culture No. 141), and where this culture was not used we l ave 
made sure that we have used a pathogenic organism corresponding in 
ordinary cultural characteristics. 
INOCULATION EXPERIMENT 
A very considerable number of inoculation experiments have been 
made in connection with demonstrating the pathogenicity of the organism 
isolated, testing the strains following growth in culture for different 
periods, and for comparison with other bacterial leafspots of tobacco, 
particularly wildfire. Repeated trials have also been made comparing 
inoculation by spraying and by needle puncture, under very variable 
environmental conditions. It has been found that, while good infection 
is always secured on wounded leaves with a virulent strain of the Wis¬ 
consin leafspot organism, practically no infection at all has ever been 
secured by simply spraying the plants with a suspension of the organism 
in water. 
The writer can not state with certainty the relation of normal field 
infection to wounded tissue. He has not been able to find from observa- 
