INFLUENCE OF TEMPERATURE, MOISTURE, AND OXY¬ 
GEN ON SPORE GERMINATION OF USTILAGO AVENAE ‘ 
By Edith Seymour Jones, Formerly Scientific Assistant, Ojficeof Cereal Investigations, 
Bureau of Plant Industry, United States Department of Agriculture 
INTRODUCTION 
The relation of climatic factors to the development of the smuts has 
been a matter of speculation during rather more than two decades. An 
exact determination of the influence of these factors has recently been 
undertaken by Dr. Lucille K. Bartholomew and the writer (2),* in order 
to provide experimental conditions for the determination of the smut 
resistance of certain pure lines of species of Avena. » It has been pointed 
out in that paper that in order to decide whether any given variety be 
completely resistant, its performance under conditions resulting in 100 
per cent of smut infection in susceptible plants must be ascertained. In 
determining those factors most favorable to the development of the smut 
organism, it becomes manifest that these same factors are numerous and 
closely interwoven, affecting both the host and the fungus. Their effect 
on both the host and the fungus must be distinguished if a complete 
analysis of their relation to tLe development of the disease is to be 
achieved. 
While Doctor Bartholomew and the writer were determining the effect 
of temperature and moisture {2) upon infection by Ustilago avenae (Pers.) 
Jens. (5), the writer began to study the influence of temperature upon the 
germination of the spores of this fungus. When the results of the 
infection studies began to indicate that sqU moisture is a factor controlling 
infection, the effect of this factor upon the germination of the spores was 
studied, and later the necessity of studying the relation of oxygen to 
spore germination became evident. This paper presents the experimental 
evidence which has been obtained concerning the influence of these three 
factors upon the germination of the spores of Ustilago avenae. Most of 
these experiments were performed under the guidance and with the help 
of Doctor Bartholomew, who had carefully formulated the whole problem 
in its broader aspects. 
By way of further introduction to the review of literature and the 
experiments, it may be well to state briefly the life history of the fungus 
in its relation to the infection of the I ost plant. The spores of Ustilago 
avenae overwinter mainly on the seed. The spores germinate simul¬ 
taneously with the oat seed. They rarely form germ tubes but commonly 
produce promycelia which, in turn, form either sporidia or thin hyphae. 
These sporidia, hyphae, or germ tubes infect the host through the 
coleoptile before it is pierced by the first leaf and the fungus establishes 
itself in the meristematic tissue of the growing point of the main axis 
and the tillers. Here the mycelium keeps pace with the development 
of the host, without apparent injury to it, until, at blossoming time, it 
^ Accepted for publication Aug. 21, 1923. This paper presents the results of investigations conducted 
cooperatively by the OflSce ci Cereal Investigations, Bureau of Plant Industry, and the Depirtment of 
Plant Pathology of the Wisconsin Agricultural Experiment Station. 
* Reference is by number (italic) to “ Literature cited,*’ p. 590-591. 
Journal of Agricultural Research, 
Washington, D. C 
aed 
(577) 
Vol. XXIV, No. 7 
May X9. Z923 
Key No. O-30* 
