Mar. io, 1923 
Rosette Disease of Wheat and Its Control 
787 
coleoptile tissues and in the outer underground leaf sheaths of the tillers. 
Sometimes a mild to severe infection takes place in the subcrown inter¬ 
node, but apparently this is not as common as the infection of the other 
tissues mentioned. Fall infection seems to be rarely severe, and in most 
cases tiller lesions do not penetrate beyond the first or second leaf sheath. 
Winter wheat sown early shows a higher percentage of Helminthosporium 
infection and also more severe injury therefrom than does late-sown 
wheat. 
A close study of the healthy wheat plant late in the fall and through 
the winter indicates that practically all of the outer leaf sheaths disinte¬ 
grate and become separated from the vital tissues of the tillers or in some 
cases disappear entirely. Similarly, in plants showing Helminthospo¬ 
rium infection on the outer leaf sheaths in the fall, these outer leaf sheaths 
disintegrate, leaving the inner living leaf sheaths practically free from 
lesions. This explains the comparative absence of Helminthosporium 
on and in the vital tissues of wheat plants early in the spring. In this 
connection soil-temperature experiments conducted under controlled 
conditions show that the minimum temperature for the development of 
the wheat plant is somewhat below that for the developement of Helmin- 
thosportium infection. This relationship probably explains why Hel¬ 
minthosporium does not begin its spring attack on the vital tissues of the 
plant until some little time after the wheat plant begins its spring develop¬ 
ment and also the increased fall infection of Helminthosporium in early 
sowings. 
A condition somewhat similar to rosette disease has been noted by the 
writer on Marquis spring wheat growing in soil badly infested with Hel¬ 
minthosporium. Stakman (32) also reports a similar condition in spring 
wheat growing in Helminthosporium-infested soil in Minnesota. While 
this condition does resemble rosette disease in certain respects, it differs 
in others, as pointed out by Stakman. 
Preliminary field studies made during the early winter of 1920-21 on 
Harvest Queen (white-chaffed Red Cross) wheat plants growing in soil 
known to produce the rosette disease showed that plants with fall infec¬ 
tion of Helminthosporium on the subterranean portions of the tillers and 
on the subcrown intemodes produce more tillers than plants free from 
such infection. Actual counts showed 42.5 per cent more tillers on the 
infected plants than on healthy ones. 
In order to determine the influence of Helminthosporium upon tiller 
development, sterilized soil was inoculated in the greenhouse with a 
heavy water suspension of the conidia of the Helminthosporium isolated 
from a plant affected by rosette disease. Another plot identical with 
the former in every way except that the soil was not inoculated was 
used for the control. These plots contained about 10 square feet each. 
Harvest Queen (white-chaffed Red Cross) wheat (susceptible to rosette 
disease) and Marquis spring wheat (susceptibility questionable) were 
sown in both plots. The same number of seeds was used in each plot 
and for each variety, and seeding was done under the same conditions 
in each plot. The results of this experiment, given in Table VI, show 
a stimulation in tiller development in plants of the Harvest Queen 
(white-chaffed Red Cross) wheat infected with Helminthosporium, but 
not in Marquis. 
While an increase in the number of tillers was obtained in Harvest 
Queen (white-chaffed Red Cross), this was noticed only by making 
27135—23-2 
