THE CRITICAL TEMPERATURE FOR INFECTION OF THE 
POTATO SEED PIECE BY FUSARIUM OXYSPORUM 1 
By H. G. MacMillan, Pathologist, and G. A. Meckstroth, Assistant Patholo¬ 
gist, Office of Cotton, Truck, and Forage Crop Disease Investigations, Bureau of 
Plant Industry, United States Department of Agriculture 
INTRODUCTION 
The infection of the potato ( Solarium tuberosum) seed piece by 
Fusarium oxysporum Scmect. commonly results in much disease and 
consequent economic loss in the western part of the United States. 
Of the factors influencing the development of this disease one of 
the most important is temperature, for it is an element of the en¬ 
vironment to which both host and parasite respond. The effects of 
other elements are altered by its changes. The critical temperature 
of infection—that is, the point below which parasitism fails to occur, 
and above which damage to it develops—is the point of departure for 
studies of wilting, rotting, and other manifestations of infection. 
REVIEW OF LITERATURE 
In 1919 MacMillan (<§) 2 pointed out the fact that temperature is 
vital so far as infection of the potato seed piece by Fusarium 
oxysporum is concerned. Other Fusaria and different host plants 
have received the attention of a number of workers. Gilman (S) de¬ 
termined 17° C. to be the critical temperature of infection of cabbage 
by F. conglutinans . Tisdale (9) found flax to be infected by F. Uni 
at 15° or higher. Clayton ( 1) determined 22° as approximately the 
critical temperature for infection of the tomato by F. lycopersici. 
Johnson and Hartman ( 6 ) reported that the root-rot disease of to¬ 
bacco less marked below 15°, and that a number of other soil factors 
influence the development of it. Goss (< 5 ) found that the wilt of po¬ 
tatoes caused by F. oxysporum did not develop below 18°. In the 
determination of these temperatures one type of apparatus was 
used by all, the so-called Wisconsin temperature tank, described by 
Jones (7). 
Under practical conditions no constant temperature of the soil is 
to be expected. Dickson (2) states that the mean of a fluctuating 
soil temperature develops the same condition as a constant tem¬ 
perature equal to the mean. But for the exact determination of a 
critical temperature point as constant a temperature as possible is 
desired. Goss (4) in a controlled temperature study of Fusaria rots 
maintained the temperatures with a variation of only 2° C. Other 
workers have allowed variations of these small amounts, inevitable 
from the nature and duration of the experiment. 
i Received for publication Mar. 21, 1925; issued January, 1925. 
* Reference is made by number (italic) to “Literature cited,” p. 921. 
Journal of Agricultural Research, Vol. XXXI, No. 10 
Washington, D. C. Nov. 15,1925 
Key No. G-505 
74780—26t-2 
( 917 ) 
