JOIM, OF METIAL BESEAM 
Voi.. XXIV Washington, D. C., Aprii, 7, 1923 No. i 
TEMPERATURE RELATIONS OF ELEVEN SPECIES OF 
RHIZOPUS ^ 
J. h. WmMBR and L. L. Harter, Pathologists^ Office of Cotton, Truck, and Forage 
Crop Disease Investigations, Bureau of Plant Industry, United States Department 
of Agriculture 
INTRODUCTION 
Harter, Weimer, and Lauritzen {12) ^ have recently shown that the 
typical softrot of sweet potatoes may be produced by nine different 
species of the genus Rhizopus. It has been demonstrated likewise that 
these fungi can produce a similar decay of a large number of fruits and 
vegetables when the host and parasite are brought together under 
suitable conditions (u). The importance of temperature as one of the 
conditions essential for infection by these fungi was pointed out, it 
having been found necessary in all cases to expose the hosts to tempera¬ 
tures within the range most suitable for the growth of the fungus in 
order to obtain infection. These fungi were placed roughly into high, 
low, and intermediate temperature groups. More recent studies have 
been made ® in which the temperature limits for growth of these fungi 
upon the sweet potato have been determined. The behavior of these 
fungi upon the living host is of special interest, since it is under these 
conditions that they become of economic importance. However, in 
studies of this nature two Hving organisms are involved, each of which 
may respond quite differently to various conditions of the environment. 
At high temperatures the physiological activities of the host are ac¬ 
celerated, while the reverse is true at low temperatures. The growth 
of the fungus will likewise be stimulated or retarded, depending upon 
the temperature employed; consequently any living host as a medium 
for testing the response of the species of Rhizopus to temperature would 
not be uniform at different temperatures and would therefore be unsatis¬ 
factory. It was the object of these investigations to determine the 
influence of temperature on the development of 11 species of Rhizopus 
when grown upon an artificial culture medium of uniform composition. 
The studies, the results of which are presented below, include lie effect 
of temperature first on the germination of the spores, second on the growth 
of the mycelium, and third on the fruiting of the fungi. 
SPECIES STUDIED 
The species of Rhizopus studied were the same as those used in former 
investigations: Namely, nigricans Ehrnb., reflexus Bainier, chinensis Saito, 
1 Accepted for publication May ag, igaa. 
* Reference is made by number (italic) to “Literature dted/' p. 39"4o. 
* By J. I. Lauritzen, of the Office of Cotton, Trudc, and Forage Crop Disease Investigations, Bureau of 
Plant Industry, United States Department of Agriculture. The results have not yet been published. 
Journal Agricultural Research, 
Washington, D. C. 
abe 
30615—23 - 1 
(I) 
Vol. XXIV. No. X 
Apr. 7,1993 
Key No. G-294 
