Fusarium in Tuber Rot and Wilt of Potato 
31 
It should be noted here that F . trichothecioides when inoculated 
into a tuber can grow at 30° C, while it cannot do so in artificial 
media; and that F. oxysporum can survive a temperature of 1° C. 
in artificial media, but not in the tuber. 
TABLE IV 
Condition of tubers at close of experiment 
Temperature 
Fusarium oxysporum 
Fusarium trichothecioides 
30° C 
All completely rotted; 
sprouts killed 
All completely rotted; 
sprouts killed 
All with very slight rot 
No rot 
Slight rot in one tuber 
No rot 
No rot 
Slight rot in some 
All completely rotted; 
some sprouts killed 
All completely rotted 
All with slight rot 
All completely rotted 
No rot 
All completely rotted 
25° C 
12° C 
1° C 
1° C. for two weeks, then 
25° C. for two weeks. . 
— 1° C 
— 1° C. for two weeks, then 
25° C. for two weeks. . 
Discussion. — These results may, in part at least, explain why 
F. oxysporum, even though it can attack parenchyma and rot tubers, 
usually is not found in rotted tubers, while F. trichothecioides is. 
The ability of the latter to make a faster initial growth at the 
temperatures which prevail in the soil about digging time and in 
well kept storage places is probably the determining factor in this 
phenomenon. The experiments with tubers showed that F. tri- 
chothecioides made a great increase in growth rate when transferred 
from a low to a higher temperature. 
These temperature relations may also explain in part the fact 
that we usually find F. oxysporum producing wilt under field con- 
ditions, and lend support to the observations made by Ortox (27), 
who reports potato wilt induced by Fusarium spp. to be pre- 
eminently a warm climate disease. F. trichothecioides can produce 
wilt, but the temperature conditions in the soil are such as to favor 
F. oxysporum, the maximum temperature of the former being 
the optimum of the latter. Humphrey (15), working in Washing- 
ton on the tomato wilt induced by F. oxysporum, came to the con- 
clusion that temperature differences in various parts of the state 
were determining factors for the appearance and non-appearance 
and severity of the disease. 
