844 
Journal of Agricultural Research 
Vol. XXIII, No. ii 
in the concentration of inoculum, there were gradual increases in both the 
percentage of seedlings killed preceding emergence and the percentage of 
those wilted following emergence (Table I and fig. 3). In the more dilute 
suspensions the attack was usually restricted to the subcrown internode 4 
and resulted in a slight blighting, from which in many cases the seedlings 
recovered. As the number of conidia increased, however, the attack 
became more general, often including the young plumule, thus resulting 
in the higher percentages of seedlings which blighted before emergence. 
A combination of a heavy conidial suspension, together with conditions 
favorable for the development of the blight, usually resulted in high per¬ 
centages of the seedlings being killed before emerging (PI. 5, A). 
Tabi,B I .—Relation of number of conidia to the production of seedling-blight of wheat 
and to the type of blight produced 
Average num¬ 
ber conidia per 
cubic centimeter 
of inoculum. 
Percentage 
germina¬ 
tion of 
wheat. 
Percentage 
of plants 
emerged. 
Percentage 
of disease- 
free plants. 
Percentage of blighted plants. 
Slightly 
diseased. 
Wilted. 
Blighted 
before 
emerging. 
Control 
99 
98 
85 
13 
O 
I 
13, 200 
97 
80 
60 
r 3 
7 
17 
65,000 
99 
78 
56 
9 
13 
21 
325,000 
93 
65 
43 
7 
15 
28 
1, 625, 000 
90 
45 
18 
6 
21 
45 
The two intermediate spore dilutions seemed to give the most uniforni 
results. The first, 65,000 conidia per cubic centimeter, gave a medium 
percentage of both wilt and blight, whereas the second dilution, 325,000 
conidia per cubic centimeter, gave a relatively higher percentage of 
seedlings blighted before emergence. Consequently these two spore 
dilutions were used for inoculation purposes in the soil-temperature 
and soil-moisture experiments reported in this paper. 
TEMPERATURE AND MOISTURE EXPERIMENTS IN THE GREENHOUSE 
INFLUENCE OF TEMPERATURE ON THE PARASITE 5 6 
A considerable literature has been accumulated on the influence of 
temperature, moisture, and other environing conditions on the develop¬ 
ment of both saprophytic and parasitic species of the genus Fusarium. 
Schnaffnit (25), Humphrey (18), Gilman (ji), Tisdale (30), and others 
have found that, in general, these organisms develop best at compar¬ 
atively high temperatures. Their results, however, show that while 
this group of fungi have fairly high optima, yet they have a very wide 
temperature range, spore germination, vegetative development, and 
spore production taking place at a range of from 5 0 to 36° C. 
4 The designation “ subcrown intemode,” as used for wheat in this paper, applies to the structure between 
the base of the coleoptile and the crown node. 
6 From unpublished data of experiments conducted by Helen Johann, Grace O. Wineland, and the writer 
in the Office of Cereal Investigations, Bureau of Plant Industry, United States Department of Agriculture. 
