Fusariiim Blight of the Soy Bean 
37 
It is to be noted that all of the plants in the last test were 
infected with nematodes but that the cowpeas were more severely 
affected, the galls being somewhat larger and more numerous. 
The cowpeas generally showed symptoms of the fungus whether 
the eelworms were present or not. The soy beans remained free 
from the fungus in spite of nematode injuries. The galls on 
the SO}" beans did not reach a diameter of more than 1 to 2 mm. 
whereas in the fields wliere the blight developed they were 
commonly 8 to 10 mm. in diameter. The presence of the galls 
even tho small, and the absence of the fungus on the roots of 
plants in soil infected with both organisms in this and the two 
other tests mentioned, is evidence that the presence of nematodes 
under conditions which favor the development of the fungus on 
cowpeas does not supply the conditions that obtain in the field, 
which allow the development of this fungus on soy beans. 
THE INFLUENCE OF SOIL TEMPERATURE 
Eecent reports of various investigators point out the relation 
of temperature to diseases caused by soil inhabiting fungi espe- 
cially species of Fusarium. Jones (15) emphasizes the impor- 
tance of this factor by summarizing the results of these investiga- 
tions and correlating them with his own field observations. In 
main the results with Fusarium spp. show a minimum tempera- 
ture for infection around 15° to 17° C. and a rather broad 
optimum of about 25° to 30° C. As far as the writer is aware, no 
data on maximum temperatures have been reported. 
Before attempting to determine the influence of certain tem- 
peratures on soy bean blight, the organism was tested in culture 
at constant temperatures of 5°, 8°, 12°, 16°, 20°, 28°, and 33° C. 
After 10 days at 5° there was practically no growth, at 8° the 
colonies averaged 1 or 2 mm. in diameter, at 12° they were about 
5-7 mm., at 16° about 18-20 mm., and with a rise in temperature 
to 28° a corresponding increase in size of colonies. At 33° the 
^ growth was somewhat less than at 28°. Cultures of the other 
I wilt producing species of Fusarium reported by others correspond 
rather closely in their growth at these temperatures, 
f The optimum condition for infection in the case of soy bean 
i blight may, however, be entirely different from that which is 
I favorable to either parasite or host. Experiments are now in 
! progress in which soy beans are growing in inoculated soil main- 
tained at various constant temperatures. Nothing of significance, 
however, can at present be reported as to the relation of this 
I factor, except that the amount of disease has not been increased 
I at 14, 16, 17, or 24 degrees Centigrade. 
