A STUDY OF THE ENVIRONMENTAL CONDI- 
TIONS INFLUENCING THE DEVELOPMENT 
OF STEM RUST IN THE ABSENCE OF 
AN ALTERNATE HOST 1 
I. THE VIABILITY OF THE UREDINIOSPORES OF PUCCINIA 
GRAMINIS TRITICI FORM III 
GEORGE L. PELTIER 
INTRODUCTION 
No exact data are at hand regarding the influence of tempera- 
ture and relative humidity on the viability of the urediniospores 
of stem rust under controlled conditions. What statements do 
appear in the literature are general and are of no specific value 
in that no stated temperature or relative humidity is given. The 
few chapters devoted to the subject of the viability of the ure- 
diniospores by Levine 2 in his review of the literature on “The 
Epidemiology of Cereal Rusts 7 ’ may be cited as an illustration of 
our lack of knowledge on this subject. 
In order to determine more accurately the viability of the 
urediniospores of stem rust of wheat under controlled conditions, 
a modification of the method developed by the writer 3 in his 
viability study of Pseudomonas citri Hasse was employed. 
Briefly, this consisted of subjecting uredinia of approximately 
the same age on detached wheat seedling leaves to various combi- 
nations of constant temperatures and relative humidities. At 
weekly intervals, both germination tests of the urediniospores in 
the laboratory and infection tests in the greenhouse were made. 
APPARATUS USED 
Temperature controls. — For temperatures of 25° and 30° C., 
ordinary bacteriological incubators were employed. For tempera- 
arrangements have been made whereby the publication of the various 
phases of this project will appear from time to time as Research Bulletins 
of the Station. Thus, all publications by the author dealing with this proj- 
ect will be issued from one source, so that uniformity, in the presentation 
of the results will be assured. 
2 Levine, M. N'. The Epidemiology of Cereal Rusts in General and of 
the Black Stem Rust in Particular, p. 33-34, 1919. Office of Cereal Investi- 
gations, Bureau of Plant Industry, United States Department of Agricul- 
ture. Mimeographed. 
3 Peltier, G. L. Influence of Temperature and Humidity on the Growth 
of Pseudomonas citri and its Host Plants and on Infection and Develop- 
ment of the Disease. Jour. Agr. Research 20:488-491, 1920. 
