Apr. 26, 1924 
Studies on Curly-Top Disease of the Sugar Beet 311 
EFFECT OF HEAT ON THE VIRUS 
The question as to whether or not the virus of curly-top is destroyed by rela¬ 
tively high temperatures was studied by placing nonviruliferous leafhoppers on 
parts of curly-top beets which had been immersed in water at the desired tem¬ 
perature. The root pieces were cut so that in no case was the thickness greater 
than 1 cm. A period of 10 minutes was used in each experiment. After the 
leaves or root pieces had been immersed in the heated water, nonviruliferous 
insects were caged on these beet parts for 24 hours and then removed to healthy 
plants. The results of the experiments are shown in Table IX* It should be 
noted that in the cases where the insects failed to secure the virus from heated 
leaves the leaves were so decomposed by heat as to be unfit for food. The results 
of the experiments seem to indicate that the virus is not destroyed by tempera¬ 
tures lower than those at which the beet tissue is killed. Many bacterial parasites 
of plants are killed by temperatures lower than those which the curly-top virus 
will endure. 
Table IX .—Effect of the application of heat on the virus of curly-top 
Season, experiment, and date 
Season of 1919: 
Number lttgffll!;; 
Number 2{May| ::; 
Number 3, June 6. _. 
Number 4, August 7. 
Season of 1920: 
Number 6, April 14. 
Season of 1921: 
Number 0 
October 14. 
October 20. 
October 20. 
October 20. 
{ 
Tem¬ 
perature 
of water 
used 
Parts of diseased plant 
heated 
Results 
(°0.) 
45 to 46 
54 to 55 
45 
50 
49 to 50 
49.5 to 50 
51 to 52 
51 to 52 
Leaves 
_do. 
Leaf. _ 
_do. 
Leaves 
_do. 
_do. 
_do. 
51 to 52 
52 to 53 
60 to 61 
60 to 61 
Leaves and root pieces 
.....do.-. 
Leaves. 
Root pieces--..... 
Plants diseased. 
Plants healthy. 
Plants diseased. 
Plants healthy. 
Plants diseased. 
Do. 
Do. 
Do. 
Do. 
Do. 
Plants healthy. 
Plants diseased. 
EFFECT OF DESICCATION ON THE VIRUS 
Four tests in which dried tissue of curly-top beets was remoistened with water 
and then placed in cages as food for nonviruliferous leafhoppers have given only 
negative results. The insects were unable to produce curly-top when removed to 
healthy plants. The survival of the insects in three of the tests for periods of 
approximately 24 hours at room temperature indicates that they must have fed 
to some extent on the old diseased tissue. Further work is needed to justify the 
conclusion that the virus is destroyed by desiccation. 
DISTRIBUTION OF VIRUS IN AFFECTED PLANTS 
Those leaves which are mature at the time of infection remain normal or free 
from symptoms of the disease until they begin to yellow with age. The question 
has therefore been suggested as to whether or not these apparently normal leaves 
contained the virus or disease-causing factor. Tests have been made by the use 
of nonviruliferous leafhoppers. These insects were caged on the leaves to be 
tested and then transferred to healthy beet plants to determine if they had be¬ 
come effectively viruliferous. Eight trials of this nature have been made. In a 
few instances the insects failed to secure the virus from the old, normal-appearing 
