TOBACCO WILDFIRE IN 1922. 3 



been made in regard to the life history of the causal organism, especially 

 with reference to overwintering and dissemination. The results of the life 

 history and control work of 1922 are briefly presented in the present 

 bulletin. 



Valuable assistance in the work has been rendered by Prof. A. V. Osmun 

 of the Massachusetts Experiment Station and Mr. C. M. Slagg of the 

 United States Department of Agriculture. Tobacco growers in both 

 States, too numerous to mention here bj^ name, have co-operated heartily 

 with the writers in the work described in the following pages. 



LIFE HISTORY STUDIES. 



Overwintering of the Bacteria. 



As a basis for control measures, probably no problem in regard to life 

 history of the causal organism^ is more important than determination 

 of the method or methods by which the bacteria survive the winter 

 and thus serve as starting points. for wildfire of the next year. Certain 

 experiments with the object of solving this 

 problem were conducted during the winter of 

 1921-22, and though some of the results are 

 not conclusive progress to date is reported at 

 this time. Other experiments with the same 

 object are now in progress, and it is hoped 

 that they will be more satisfactory. 



Effect of Freezing the Bacteria. 

 In studying the problem of overwintering. 



Fig. 1. — A group of the bac- 

 teria which cause wildfire. 

 Magnified 5,CO0 times. 



the first point to be determined is the effect 

 which freezing has on the organisms. If they are not able to withstand 

 the exposure of a New England ^\dnter, then the measures of control will 

 be quite different from those which should be tried if they are resistant 

 to cold. Pure cultures of Bacterium tabacu7n on agar were placed out of 

 doors at various times during the winter of 1921-22, some of them being 

 frozen soUd for months; but in every case when they were brought back 



1 Wildfire is produced by the parasitic growth of enormous numbers of bacteria [Bacterium 

 tabacum Wolf and Foster) in the leaves. Since various investigators who have published concern- 

 ing the organism do not agree as to some of the morphological characters, Anderson during the 

 past season has made and studied permanent slides on which the bacteria have been stained by 

 (1) the Duckwell modification of the Pitfield method, (2) the Shunk method (Journ. Bact. 5: 181, 

 1920), and (3) to a less extent by other methods. The organisms are short, cylindrical rods with 

 rounded ends and usually straight sides, but not infrequently individuals are found which are 

 slightly curved or somewhat dumb-bell shaped. EYequently two or three of them remain end 

 to end in a chain on the slide. Those in chains are shorter, indicating immaturity. Only those 

 which were free from each other were used in measuring. The average size of fifty taken from 

 five slides stained in different ways was 2.3x.8 n. The longest one measured was 3.8 m and the 

 shortest 1.4 n. Attached to one end there are one to four flagella several times as long as the body 

 of the bacterium. The bacteria in text. Fig. 1, were drawn from a slide stained by the modified 

 Pitfield method. 



