PATHOGENICITY OF OPHIOBOLUS CARICETI IN ITS 
RELATIONSHIP TO WEAKENED PLANTS 1 
By H. R. Rosen and J. A. Elliott, Arkansas Agricultural Experiment Station 
In the United States the “Australian take-all’* of wheat was first 
reported in 1920 2 (d), 3 from New York. The following year it was dis¬ 
covered by the writers in Arkansas. 4 As the field observations strongly 
suggested that the fungus, Ophiobolus cariceti , found on diseased wheat, 
was a weak parasite, attacking plants which were more or less unthrifty, 
experiments were undertaken to obtain more information on this point. 
When Ophiobolus was first found in this country it was regarded with 
such alarm that gasoline was poured over the infested area and the 
plants burnt (d). This measure doubtless was justified inasmuch as the 
disease had been considered a serious one by investigators in Australia 
and in European countries, and the discoverers may have had in mind 
the possibility that the disease had been recently introduced into this 
country and was confined to a small area. 
In May, 1921, Mr. O. Pool, a farmer living about 4 miles west of 
Fayetteville, Ark., brought into the laboratory diseased wheat showing 
marked blackening at the bases of the culms. (See PI. 1 and 2.) The 
plants were much stunted, and the roots were largely dead and bunchy, 
with abnormal development of woolly root hairs on parts adjoining the 
stools. Blackish crusts of mycelium surrounded bases of culms, and 
extended into the enveloping leaf sheaths, and, finally, black, beaked, 
fruiting bodies, quite noticeable under a hand lens, were found sub¬ 
merged in the lower parts of the sheaths; when these were examined 
nnder the microscope, asci and spores, typical of Ophiobolus, were found. 
FIELD OBSERVATIONS 
The writers immediately went to the field from which the plants had 
been obtained and saw 11 acres of very sickly looking wheat. The field 
was undulating, with elevated spots on the eastern and western borders 
and a low area in between, which, according to Mr. Pool, became a good 
sized pond during rainy seasons, being flooded with water for two or 
three months at a time. The soil even on the elevations appeared poorly 
drained, with crawfish holes very noticeable. It is classed as Gasconade 
silt loam, a type, grayish white in appearance, which is usually poorly 
drained in this region, often giving an acid reaction, as this soil did. 
The stand of wheat as a whole was poor (PI. 3), the heads, even 
on the best plants, were undersized (by the end of May, wheat is 
usually well developed in this latitude), and bare spots were noticeable 
throughout the field. Many of the plants were stunted, 6 and 12 
inch plants were bearing heads, and were either dead or about to die; 
1 Accepted for publication June 25, 1923. 
a The disease of wheat first found in Madison County, Ill., in 1919 and at one time considered as “Aus¬ 
tralian take-all/’ or “so-called take-all,” is now considered by McKinney, Eckerson, and Webb ( 8 ) as a 
“rosette disease" associated with intracellular bodies comparable to those found in various mosaic diseases. 
Stevens ( 11 ), in considering the footrot stage of the disease, has concluded that this is due to Helmintho- 
sporium. 
■ Reference is made by number (italic) to “Literature cited," p. 358. 
4 U. S. Department op Agriculture. Bureau op Plant Industry. Plant Disease Survey, 
wheat, the take-all survey. In U. S. Dept. Agr. Bur. Plant Indus. Plant Disease Bui., v. 5, p. 4. 
19a 1. (Mimeographed.) 
Journal of Agricultural Research, 
Washington, D. C. 
agd 
(3s 1 ) 
Vol. XXV. No. 8 
Aug. 25,1923 
Key No. Arlc-4 
