Apr. 7, 1923 
Influence of Soil Temperature on Fusarium in Cabbage 83 
whereas there is little or no development even in the sickest'^ soils 
during moist, cool weather. 
(2) Hot, dry weather also retards the growth of cabbage plants. 
(3) During such critical periods they become pale green in color and 
show a general lack of vigor; even the resistant Wisconsin Hollander 
shows a considerable percentage of incipient yellows. With the return 
of favorable rainfall and lower temperature the resistant plants over¬ 
come the attack of yellows and produce marketable heads. 
(4) Such field observations soon convince one that the occurrence 
and severity of yellows are closely correlated with the influence of soil 
temperature and soil moisture, and the question arises as to how far 
and in what way these influences relate to the host on the one hand 
and to the parasite on the other. 
(5) The commercial varieties have shown considerable differences 
in degree of resistance to Fusarium. Also, within any one variety 
there is always a variation in resistance as between individuals. During 
severe seasons most of the plants of the standard commercial varieties 
quickly succumb to the disease; others linger along in a dwarfed con¬ 
ation, slowly shedding their lower leaves, whereas a few scattered 
individual plants in the field usually remain healthy and produce mar¬ 
ketable heads. This variation in individual susceptibility or disease 
resistance has been the basis for developing the resistant Wisconsin 
strains. 
(6) The preceding observations and experiments were made upon 
plants which had been transplanted into the field. 
(7) Gilman (S), in his greenhouse experiments, showed that yellows 
did not develop below 17^ C. while it developed quite destructively at 
23° to 25®. He also studied the effect of certain temperatures upon the 
growth of the fungus in culture, but he did not define the upper tem¬ 
perature limits either for its growth or for the occurrence of the disease. 
(8) The writer undertook to learn more exactly the factors regarding 
these questions, using seedling cabbage plants. The purposes outlined 
were: (i) To determine the range of soil temperature for the occur¬ 
rence of yellows in cabbage seedlings, the air temperature being kept 
constant; (2) to study the influence of soil temperature upon the growth 
of cabbage seedlings in noninfested soil; (3) to determine in like manner 
the influence of soil moisture both upon the growth of cabbage seedlings 
and upon the occurrence of yellows in them; (4) to study the influence 
of high soil temperature and soil moisture upon the susceptibility of the 
resistant strain, that is, upon the “breaking down'* of resistance. These 
experimental investigations have justified several conclusions bearing 
upon these questions as follows. 
(9) Pure cultures of Fusarium conglutinans on potato agar plates 
showed the following relations to temperature: (i) The organism grew 
at temperatures ranging from 7° to 35° C.; (2) the optimum temperature, 
using diameter of colony as a criterion, at the end of 7 days was 25® to 
(3) although no ^owth took place in 7 days at 37°, the organism was 
not killed at this temperature. 
(10) Cabbage yellows develops in seedlings growing in ‘^sick** soil at 
soil temperatures ranging from 17° to 35° C. At 17"^ it devdops very 
slowly even in the most susceptible strains. In naturally infested soil 
the disease appears first and develops most rapidly in both resistant 
and susceptible strains at 26® to 29° and in steiflized artificially inocu¬ 
lated soil at 29® to 32®. 
