WHITE BURLEY TOBACCO RESISTANT TO ROOT-ROT. 5 



of the United States in recent years have shown that the damage 

 annually runs into millions of dollars. The loss in Kentucky alone 

 must easily exceed on the average $2,000,000 yearly. 



CAUSE OF THE DISEASE. 



The root-rot is caused by a fungus which lives as a parasite on the 

 roots of the plant. This organism, or germ, although so small that 

 it can not be seen except with a high-power miscroscope, is still a 

 very large organism as compared with other parasites which pro- 

 duce well-known diseases in plants and animals. This organism is 

 called Thielavia basicola, and technically this disease should be called 

 the Thielavia root-rot, since there are many other organisms which 

 cause root diseases in other plants. This fungus can grow into the 

 roots of the tobacco plant and feed on its tissues, which results in 

 their decay. Moreover, it can live on dead organic material in the 

 soil, though not as readily, and in the absence of the tobacco plant 

 from the soil it gradually dies out, though this may require from 5 to 

 10 years or more. The exact time has not yet been determined, but 

 it probably varies somewhat with different types of soil. The disease 

 spreads very much in the same way as other diseases of plants and 

 animals, ft is sometimes very difficult to account for the first infec- 

 tion by the fungus. The most common means of spreading it is 

 through the transference of sick soil, either by wind, water, or 

 animals, to healthy soil or by the transplanting of diseased plants 

 from infested seed beds. 



With this description of the nature and cause of the disease, the 

 skeptical grower has still the right to ask for proof that the root-rot 

 is doing the amount of damage claimed and that it, and not depletion 

 of soil fertility, is the reason why tobacco soils in the Burley section 

 require several years of " rest " after having grown one, two, or 

 three crops of tobacco. There exists, fortunately, a convenient and 

 convincing proof of this fact. This lies in varietal differences in re- 

 sistance and susceptibility to the disease. 



VARIETAL RESISTANCE AND SUSCEPTIBILITY. 



It is now a well-established fact that plants as well as animals 

 differ in their degree of susceptibility to disease. This is now known 

 to hold true for the tobacco plant as regards the Thielavia root-rot. 



If two varieties of tobacco, Connecticut Havana and White 

 Burley, for instance, are planted side by side on ground which has 

 just grown two or three crops of Burley, the Havana seed in most 

 instances will produce at the end of the season from two to a hundred 

 times as much weight as the Burley. If, however, these two varieties 

 are planted on ground on which tobacco has not been grown for 



