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. 
e 
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 
soul, 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 
1Q 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. It 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 
