a BULLETIN 1347, U. S. DEPARTMENT OF AGRICULTURE 
cbtained in experimental material and then only occasionally when 
large amounts of inoculum were used. The writer has not observed 
this type of blackening in nature, though there seems to be no reason 
why it would not occur if the proper conditions were obtained. He 
has never found Helminthosporium sativum producing a mycelial 
crust or plate in any way similar to that produced by O phiobolus 
graminis. Weniger (74) reports that a black coloration is sometimes 
associated with Helminthosporium foot-rot in spring wheat in North 
Dakota, but she does not state the exact nature of this coloration. 
Christensen (73) states that spring wheats and barley may show 
excessive tillering and_become stunted when infected by Helmin- 
thosporium sativum. In this regard there seems to be a similarity 
to the rosette disease (44) SESE in certain varieties of winter 
wheat. Although the writer (44) has mentioned that certain spring 
wheats and barleys infected by this parasite develop symptoms simi- 
lar to rosette, he has never noted that these crops develop the same 
degree of tillering or certain of the other symptoms which occur in 
winter wheats affected by rosette. Data have been published (44) 
which indicate that H. satevwm will increase tillering in Harvest 
Queen (winter) wheat, but this condition was not associated with 
any abnormal appearance of the aboveground portions of the plants. 
Stevens (66, 6 j7) has stated that the rosette disease (called foot-rot 
by him) occurring in winter wheat is caused by Helminthosporium 
sativum, but it has been pointed out several times by the writer (43, 
44, 43) that this causal relationship has not been demonstrated. 
Evidence (49) now in hand indicates that H. sativum is not the 
rimary causal agent for the rosette disease. 
Several field inoculation experiments carried out by R. W. Webb 
and the writer with pure cultures of Helminthosporium sativum have 
failed to produce symptoms of the rosette disease in Harvest Queen 
wheat, a variety which 1s highly susceptible to rosette. In these 
experiments a culture of H. sativum was used kindly supplied by 
F. L. Stevens. This culture was isolated by him from a wheat plant 
affected by the rosette disease and the Helminthosporium foot-rot. 
Other cultures of H. sativum isolated by Webb and the writer also 
were used in these inoculations. In addition, field soil of long- 
standing infestation with H. satevum was kindly supplied to the 
writer by J. J. Christensen, of the Minnesota Agricultural Experi- 
ment Station, and this soil. also failed to produce any suggestion of 
the rosette disease on Harvest Queen wheat. Experiments carried 
on at the same time and under the same conditions with soil naturally 
infested with the rosette causal agent invariably developed a high 
percentage of rosette.” 
CAUSE OF THE DISEASE 
As pointed out recently by Drechsler (79) and by the writer (45), 
Johnson (35) appears to be the first to show that Helminthosporium 
sativum is pathogenic on wheat plants. Several other workers (13, 
43, 44,65, 66) also have carried out inoculation tests with this organ- 
ism and concluded that it is pathogenic on wheat. In the present 
12 Experimental evidence received after this buftetin was prepared for the printer indi- 
cates that the rosette disease is a severe expression of a transmissible mosaic, the virus 
of which persists in certain types of soil for several years. See McKinney, H. H., A 
ies aic disease of winter wheat and winter rye. U.S. Dept. Agr. Bul. 1361, 10 pp., illus., 
1925 
