Dec. 8,1923 
Fusarium Stem and Rootrot of Peas 
467 
Table IV, showing the temperatures at which wilting took place, indi¬ 
cates very clearly the optimum temperature range for the development 
of the disease. It extends from 24 0 to 33 0 C., the upper limit of tempera¬ 
ture at which the pea plant will thrive. But damage to the pea plant 
occurs below this optimum range. At the conclusion of this series all 
plants except those grown at 15 0 C. were washed from the soil and exam¬ 
ined. The remaining plants at 24 0 C., which were dwarfed, showed decay 
of the cortex at the base of the stem, including usually a discoloration of 
the vascular system beneath the decayed area, but not extending above. 
Had they been allowed to continue to grow there is little likelihood that 
they would have survived to produce seed. 
The plants grown at 18 0 C. soil temperature showed very slight super¬ 
ficial discoloration of the cortex. They had suffered very little injury. 
Those at 21 0 C. were for the most part discolored for a short distance 
above the attachment of the cotyledons all the way to the vascular 
system, and some had discolored vascular tissue beneath the decayed 
cortex. In order to determine if these plants had suffered retardation 
of growth up to this time, the tops and roots were weighed separately. 
The result is given in the following table: 
Table V .—Average dry weight in grams of tops and roots of pea plants grown from 
January 6 to February 12 at the soil temperatures indicated in steam-sterilized soil and 
in soil inoculated with Fusarium martii pisi 
Temperature. 
Treatment. 
Number 
of plants. 
Average 
weight of 
tops. 
Average 
weight of 
roots. 
°C. 
21 . 
Control. 
16 
24 
17 
24 
Grams. 
.208 
. 192 
. 198 
.200 
Grams. 
•045 
.048 
.029 
.036 
21. 
Inoculated. 
l8. 
Control. 
l8. . 
Inoculated. 
It is readily seen from this table that up to this time the apparent 
damage had not produced any material retardation in the development 
of the inoculated plants. 
The plants from one of the pots of inoculated soil held at 15 0 C. were 
washed and no trace of injury was discovered. The remaining two pots 
of inoculated plants and two pots of controls were transferred to the 
tank maintained at 27 0 C. until the conclusion of the experiment two 
weeks later, when the plants were in full bloom. The inoculated plants 
were then notably shorter and less thrifty in appearance. The bases of 
the stems of the inoculated plants were brown and shrunken with dis¬ 
colored vascular strands in a few cases. The dry weight of the tops of 
16 inoculated plants was 7.1 grams, while that of the same number of 
controls was 8.67 grams. The root systems were almost exactly equal 
in weight. Thus tliese inoculated pea plants had begun to suffer from a 
relatively brief period of temperature favorable for the development of 
disease, even though wilting had not occurred. In all inoculation experi¬ 
ments wilting of pea plants has rarely resulted when the fungus has 
gained access to the vascular system after the early stages in the devel¬ 
opment of the plant. 
These experiments in which the effect of an extended range of soil 
temperatures upon the development of the disease has been determined 
