RELATION OF SOIL TEMPERATURE AND SOIL MOISTURE 
TO INFECTION BY PLASMODIOPHORA BRASSICAE 1 
By John Monteith, Jr. 
Assistant Pathologist , Office of Cotton, Truck , and Forage Crop Disease Investiga¬ 
tions, Bureau of Plant Industry, United States Department of Agriculture 
INTRODUCTION 
The peculiar nature of the clubroot disease of crucifers has focused upon it 
the attention of both mycologists and plant pathologists ever since Woronin 
first proved (21 ) 2 that it is caused by the parasitic slime mold. As a result there 
is an extensive literature dealing with both the scientific and the practical 
aspects of this malady. The life history of the organism is now very well under¬ 
stood and the recent studies by Kunkel (12) seem to give a satisfactory explana¬ 
tion of its relation to the host tissue. These more fundamental scientific studies 
seem to have proceeded more satisfactorily than those dealing with control 
measures. Following the early lead of Halsted (7, 8) American phytopatholo¬ 
gists have generally relied on the use of lime as an adequate control measure, 
and Ravn (lit, IB) has been an earnest advocate of liming for this disease in 
Europe. The results, while justifying the use of lime, have not proven uniformly 
reliable in either America (9) or Europe. Moreover plants that show early 
infection will sometimes recover (6) and produce a satisfactory crop. 
The evidence seems to indicate that while soil reaction is important in govern¬ 
ing infection with this parasite there must be other factors exercising an impor-. 
tant and, perhaps at times, a controlling influence upon either its entrance into 
the host tissue or upon the subsequent development of the disease. It seems 
evident, therefore, that a fuller and more exact understanding of the factors 
influencing infection and the progress of the disease may contribute both to our 
understanding of the physiological relation of parasite and host and to the 
furthering of reliable control measures. 
In this disease we afe dealing with an organism which persists for some time 
in the soil and the attacks of which are practically confined to the underground 
host organs. The recent studies at Wisconsin (11, 19) upon the influence of 
environment upon other root diseases suggest that soil temperature and soil 
moisture may be expected to play an important part in determining the occur¬ 
rence or severity of such diseases. The present paper deals with the results of. 
efforts to determine the influence of these two factors. 
EARLIER OBSERVATIONS 
Differences in the prevalence and severity of clubroot have frequently been 
attributed to variations in “climatic conditions/' but few attempts have been 
made to analyze these conditions as to their effect upon the disease. Clubroot 
is reported as causing most damage in northern regions of the United States and 
Europe, from which it might be inferred that temperature plays an important 
- part in its distribution. It has long been recognized that affected plants are 
more likely to wilt and die in periods of hot, dry weather during July and August, 
than at other times. This has been interpreted as the result of increased trans- 
i Received for publication February 1,1924. 
* Reference is made by number (italic) to literature cited, p. 559-561. 
Journal of Agricultural Research, Vol. XXVIII, No. 6 
Washington, D. C. 1924 
Key No. 0-425 
96030—241*-5 
(549) 
