STUDIES ON THE PARASITISM OF UROCYSTIS TRITICI 
KOERN., THE ORGANISM CAUSING FLAG SMUT OF 
WHEAT 1 
By ROBERT J. NOBLE* 
Assistant Biologist , Department of Agriculture , New South Wales, Australia, formerly 
Collaborator, Office of Cereal Investigations, Bureau of Plant Industry, United States 
Department of Agriculture 
INTRODUCTION 
Flag smut of wheat is a disease which now occurs in a number of the 
important wheat-growing regions of the world. It has been known to 
exist in certain countries for many years, in others it has appeared for 
the first time only recently. In some countries and in some localities, it is 
not regarded as a very serious disease of wheat, but in others it is a dis¬ 
ease of major importance, and its menacing spread is viewed with some 
alarm. 
The disease has been studied by investigators from time to time, but 
many essential points are lacking in our knowledge of the reaction of the 
pathogene to its environment and its relationships within the host. The 
present studies, therefore, were directed toward an elucidation of some 
of these phases of the parasitism of the causal organism, Urocystis tritici 
Koera. 
HISTORY, GEOGRAPHIC DISTRIBUTION, AND ECONOMIC IMPORTANCE 
Flag smut is one of the most destructive diseases of wheat. Under 
certain conditions it may exist in a locality for several seasons before its 
presence is suspected; and sometimes the disease has only been discov¬ 
ered after it has become epidemic. 
McAlpine (29) 3 states that flag smut was first recorded from South 
Australia in 1868, although there is evidence that it was fairly wide¬ 
spread before that time. The disease has now been reported in Aus¬ 
tralia from Queensland, New South Wales, Victoria, and South Aus¬ 
tralia. There is as yet no record of its occurrence in Western Australia 
or Tasmania. 
The disease was reported by Hori ( 18 ) in Japan in 1895, and Sydow 
and Butler (47, p. 427) recorded it from Lyallpur, India, in 1906. Reed 
and Dungan (42) report that it occurs in southern Europe. Dr. E. C. 
Stakman collected wheat affected with flag smut at Rieti, Italy, June 
21, 1922. 
1 Received for publication Nov. 23, 1923. The investigation herein reported was carried on while the 
writer was a Fuller traveling research scholar of the University of Sydney, Australia. It was made possible 
by cooperative arrangement with the Bureau of Plant Industry, U. S. Department of Agriculture. The 
work was done at the University of Minnesota. 
8 The writer takes pleasure in acknowledging his indebtedness to Dr. E. C. Stakman, of the Depart¬ 
ment of Plant Pathology, University of Minnesota, for advice and helpful criticism during the progress 
of the investigation. The writer also is indebted to Marion A. Griffiths, of the Office of Cereal Investiga¬ 
tions, Bureau of Plant Industry, U. S. Department of Agriculture, who is conducting studies on flag smut, 
for suggestions and access to her notes in June, 1922. 
* Reference is made by number (italic) to “ Literature cited,” pp. 487-489* 
Journal of Agricultural Research, 
Washington, D. C. 
(4s 1 ) 
Vol. xxvn. No. T 
Feb 16, X924 
Key No. G-371 
