Jan. 3,1921 Fusarium-Wilt of Tobacco 533 



No work has been done upon the selection of resistant strains within 

 individual varieties with the object of controlling the Fusarium-wilt 

 disease of tobacco. From the data presented, however, it is obvious 

 that this is a logical procedure in the control of this disease, should its 

 economic importance warrant the undertaking. The evidence at hand 

 indicates that the White Burley which was selected for its resistance to 

 Thielavia rootrot also shows marked resistance to Fusarium-wilt, as 

 compared with the ordinary White Burley, although the selection was 

 made, of course, without reference to resistance toward Fusarium. This 

 is, in fact, a step in the direction of control should the Fusarium-wilt 

 become serious in the White Burley section, where, because of the sus- 

 ceptibility of the ordinary strains grown, it is most likely to become of 

 economic importance. Selections in the Maryland Broadleaf variety, 

 which is the next most susceptible of the commercial types, seems en- 

 tirely feasible. Since it is on this type grown in Maryland that the dis- 

 ease has apparently been most common, it may be advisable in the near 

 future to undertake to select a resistant strain of this variety unless 

 other control measures are found which are more readily applicable. 



CONTROL MEASURES 



In the absence of the use of resistant varieties or strains, there appear 

 to be only the ordinary measures of control applicable to plant para- 

 sites infesting the soil. Since the disease is due to a living organism 

 which is carried over in the soil from year to year either as a parasite 

 on the tobacco plant or existing as a saprophyte in the vegetable mat- 

 ter of the soil for possibly a limited number of years, the most evident 

 measure of control seems to be the avoidance of infested soil. Espe- 

 cially when planting on new ground free from disease, it is advisable to 

 be certain also that the seedlings to be used have not been grown on in- 

 fested soil, since the parasite may be transmitted to the new soil in this 

 manner. Using new ground for seed beds or thoroughly sterilizing old 

 ground by means of steam is therefore desirable. New fields or seed beds 

 receiving surface drainage water from old, infested fields should also be 

 avoided, as should any unnecessary farm operation capable of carrying 

 even relatively small amounts of soil from infested fields to uninfested 

 ones. Where relatively few plants in a field are infected and show the 

 disease, it is a good precaution to remove these plants together with the 

 roots and to burn them so as to decrease the amount of infestation. 



SUMMARY 



(1) A disease of tobacco, apparently previously undescribed, has been 

 found to occur in Maryland and Ohio. The disease is characterized by 

 a yellowing and wilting of the leaves of the plant, usually followed by 

 death of the entire plant. The fibro-vascular system of infected plants 

 is characteristically brown or black. 



