TOBACCO WILDFIRE IN 1922. 7 



Clinton and McCormick (2: 376, 419) succeeded in one experiment in 

 infecting tobacco plants in the greenhouse by direct application of over- 

 wintered soil which had been exposed to infection the previous year. 

 Wolf and Moss (4: 30) in North CaroUna and Fromme and Wingard 

 (3: 24) in Virginia present considerable evidence that in the South the 

 organism winters in the soil, but we cannot accept this as conclusive proof 

 of the same condition in New England. 



Altogether the weight of laboratorj^ data and field observations in- 

 dicates that Bacterium tabacum is able in some cases to survive the winter 

 in the soil and start new infection from this source in the spring. On 

 the other hand, it is apparently possible under some conditions to raise a 

 clean crop of tobacco on a field that has borne diseased crops during pre- 

 ceding 3'ears. The evidence as to soil wintering is, however, not so con- 

 vincing as it should be, and further experiments are now under way which 

 it is hojDed will remedy the deficiency. 



In Cured Leaves. 



That the bacteria do not die when the diseased leaves are cured in the 

 tobacco barn has been demonstrated in a number of our experiments. 



Experiment 4. — On March 5, 1922, diseased cured leaves were taken from the 

 Hampshire County warehouse just before they were ready to go into the case. They 

 had been in the tobacco barn under normal conditions all winter. They were ground 

 to a powder in a mortar and the powder was sprinkled on wet plants in the green- 

 house. After two weeks the plants developed typical lesions of wildfire. Other 

 leaves were ground and the experiment was repeated with the same result on March 

 28. On March 8 some diseased leaves were received from Mr. H. C. Wells of Deer- 

 field. Some of them were ground and used for inoculation just as the above. Dilu- 

 tion plates were made from the others and the organism thus isolated used for 

 making inoculations. Wildfire developed on the plants inoculated in both ways. 



Experiment 5. — At Windsor, several times during the winter, wildfire spots 

 from leaves kept in the station shed were brought to the laboratory and the wild- 

 fire organism isolated in pure culture. Cultiu-es of wildfire bacteria were obtained 

 from these leaves until the middle of March in this way, and no doubt living 

 bacteria could have been found later than this. 



These experiments were conclusive and there can now be no doubt 

 that the wildfire organism can overwinter in cured leaves. It might get 

 back from the cured leaves to the next year's crop in any one of a number 

 of ways: (1) Refuse containing lesions from the shed may be thrown back 

 to the land. (2) Sash and plank are sometimes stored in the tobacco 

 sheds. Bits of broken diseased leaves could easily be carried out on such 

 sash and plank and serve to start infection in the seed-bed. (3) While 

 drawing the tobacco to the warehouse across or near the fields, parts of the 

 diseased leaves might be scattered on the land. 



Clinton and McCormick (2: 417) isolated Bacterium tabacum from 

 tobacco leaves which had been dried and kept in the herbarium for periods 

 ranging from one hundred and ninety-eight to two hundred and ninety- 

 eight daj^s. They were unable, however, to secure the bacteria from other 

 leaves which had been kept for two years. 



