Dec. 8, 1923 
Fusarium Stem and Rootrot of Peas 
465 
stant. The following table gives the average diameter of the colonies 
after seven days in a typical series. 
Table II .—Diameter of colonies of F. martii var. pisi grown on potato-dextrose agar 
seven days at the temperatures designated 
Temperature (°C.). 
10 to 11 
12 to 14 
15 to 16 
19 to 20 
24 to 25 
30 to 31 
33 to 34 
36 to 37 
Diameter (mm.). 
14 
18 
24 
44 
68 
74 
57 
16 
The optimum temperature for mycelial growth is here shown to be 
between 20° and 34 0 C. Minute growth has been observed as low as 
5-6° C. Spores are produced at all temperatures at which growth occurs. 
RELATION OF ENVIRONMENTAL FACTORS TO THE DEVELOPMENT 
OF THE DISEASE 
SOII* TEMPERATURE 
The first preliminary inoculation experiments which were made gave 
results which indicated that soil temperature modified greatly the 
rapidity with which the disease developed. In order to determine, in a 
preliminary way, the range of temperature through which infection 
takes place, planting was made as follows in soil held at controlled tem¬ 
peratures in the Wisconsin soil temperature tank. One 5-inch can at 
each temperature filled with soil from a field in which peas had never 
been grown, and which in previous trials had given plants free from 
disease, was planted with 7 Alaska peas. Two cans were filled with a 
mixture of 5 parts of this soil with 1 part of the same soil previously 
inoculated with spores of the Fusarium, and in which diseased plants 
had been produced. The amount of moisture in the soil was held approxi¬ 
mately constant through the experiment. 
Visible symptoms of disease developed first in the plants grown in 
inoculated soil at 2 7 0 C. in 20 days after planting, when 4 plants wilted 
down, and were found upon removal to be completely rotted off at the 
cotyledons, and to have vascular discoloration extending above the soil 
surface. From this time on plants continued to die with vascular 
infection at 27 0 and 30°, and finally after 35 days three plants wilted at 
24 0 C. The experiment was concluded at the end of 43 days. The 
number of plants living and dead at each temperature was as follows: 
Table III .—Number of pea plants living and dead 35 days after planting in inoculated 
and uninoculated soil at a series of soil temperatures 
