854 
Journal of Agricultural Research 
Vol. XXIII, No. II 
as all of these series were inoculated with the suspension of 325,000 
conidia per cubic centimeter, these differences can be partially ex¬ 
plained. There was, however, some evidence that Turkey wheat was 
less susceptible to the blight than the Marquis wheat. More experi¬ 
ments are necessary with these two wheat varieties to confirm these 
results. 
In comparing the influence of temperature on the parasite in pure 
culture and on the production of the blight of wheat seedlings, the 
temperature influence at first thought seems rather simple. It appears 
that wheat is capable of growing at soil temperatures lower than those 
at which the parasite can develop and become parasitic. The wheat 
plant, therefore, escapes the disease, the blight occurring only at tem¬ 
peratures which stimulate the growth of the parasite. Such a relation¬ 
ship was pointed out by Clayton 6 in the tomato-wilt caused by Fusariunt 
lycopersici Sacc., where the wilt curve produced in response to soil tem¬ 
perature coincides with the growth curve of the organism in pure culture, 
the optimum for both occurring 
at about 28° C. Upon closer 
analysis, however, the relation¬ 
ship seems far more complex and 
distinctly different from that ex¬ 
isting in the tomato-wilt problem. 
The parasite has an extremely 
wide temperature range for both 
spore germination and growth, 
and furthermore, while a histo¬ 
logical study of the wheat seed¬ 
lings at the low temperatures 
demonstrated an abundance of 
the mycelium of the parasite 
around the subterranean portions 
of the seedlings, yet no penetra¬ 
tion could be detected. The 
hyphae were twisted around the 
root hairs and matted on the 
cortex of the roots and eoleoptile. In many places swollen tips of the 
hyphae were pressed tightly into the intercellular spaces on the epidermis 
of the eoleoptile and against the root hairs, yet were seemingly unable 
to penetrate between the cells or gain entrance through the membrane 
of the root hairs, whereas at the high temperatures the hyphae readily 
penetrated any of the young seedling tissues, gaining entrance through 
the root hairs as well as through the epidermal cells of the eoleoptile, 
subcrown intemode, and roots. 
These studies, then, seemed to indicate a relationship at least between 
host and parasite almost the reverse of that in the tomato-wilt. The 
influence of environment upon the host appeared to be the fundamental 
cause of the response. The wheat seedling seemingly was unable to 
react favorably to the higher soil temperatures and thus succumbed to 
the blight. The results have shown that a short exposure to high tem¬ 
peratures during the germination period unbalanced the wheat seedling 
and thus made it susceptible to the parasite. 
v 
\ 
\ 
\ 
/ 
/ 
VS 
•CtlOrt 
L - - 
-»w/w/ t/ l 1/ 
1 III 
S !Z 46 20 24 BS 32 
jq/l nmmum: -degrces cttm&m: 
Fig. 6.—Graph showing relation of soil temperature to 
the development of seedling-blight of Turkey wheat. 
Average of seven experiments. The distance between 
the heavy and light lines shows the percentage in 
seedling-blight. Compare with spring wheat of 
figure 5. 
6 From unpublished data of studies conducted in the Department of Plant Pathology, University of 
Wisconsin. 
