JOlimOFACmTiALKEARII 
VOl. XXIV Washington, D. C., May 12, 1923 No. 6 
SPECIES OF RHI 20 PUS RESPONSIBLE FOR THE DECAY 
OF SWEET POTATOES IN THE STORAGE HOUSE AND 
AT DIFFERENT TEMPERATURES IN INFECTION 
CHAMBERS ^ 
By J. I. Lauritz^n and L. h. Harter 
Pathologists, Cotton, Truck, and Forage Crop Disease Investigations, Bureau of Plant 
Industry, United States Department of Agriculture 
INTRODUCTION 
It has been shown (6)^ that the following species of Rhizopus may 
decay sweet potatoes: Rhizopus nigricans, Ehrenb., R, reflexus Bainier, 
R. artocarpi Racib., R. delemar (Boid) Wehmer and Hanzawa, R. oryzae 
Went, and Pr. Geerligs., R. triiici Saito, R. nodosus Namysl., i?. arrhizus 
Fischer, and R. maydis Bruderl. Infection was accomplished by intro¬ 
ducing 24- to 48-hour-old cultures grown on sweet potato decoction into 
“wells” (5) made in the sweet potatoes, the “wells” being sealed over 
with a cover slip set in vaseline. The potatoes were then placed in 
moist chambers and incubated at temperatures suitable for infection 
by the species under investigation. Whether or not the capacity on 
the part of these species to decay sweet potatoes by the above-mentioned 
method is an indication of the species involved in the decay of sweet 
potatoes in the storage house at the Government experimental farm at 
Arlington, Va., and at different temperatures in infection chambers, will be 
answered, in part at least, in this paper. 
The writers^ have found, by employing the “well” method of inocu¬ 
lation, that the temperature range at which the parasitic species will 
infect and decay sweet potatoes is nearly as wide as their temperature 
growth range in artificial cultures. By this method the species employed 
have an unusual opportunity to cause infection, even to the exclusion 
of any other species ^ that might be present in the “ wells’ ’ or on the 
surface of the potatoes. It would be difiicult for any other species 
present in the “ well ” to make any headway against the mass of mycelium 
of a 48-hour-old culture. What might take place under storage condi¬ 
tions may be a different question. Here the inoculum is limited, the 
species present are in competition with each other, and all the species 
may not be present. An effort was made, therefore, to determine 
whether or not the parasitic species infect sweet potatoes over their entire 
temperature growth ranges, where infection depends upon wounding and 
the species present on the potatoes. 
Hanzawa {2) arranged the species studied by him into three groups 
according to their temperature relations. There was, as is shown by his 
1 Accepted for publication Aug. 25, 1922. 
® Reference is made by number (italic) to "Literature cited." p. 456. 
* This statement is based on unpublished data. 
* There are nearly always some Rhizopus spores on the surface of sweet potatoes and, since the only 
precaution observed to elirninate them in these experiments was by washing the potatoes, there probably 
were occasional spores present. 
Journal of Agricultural Research, 
Washington, D. C. 
aea 
(441) 
Vol. XXIV. No. 6 
May 12, 1923 
Key No. G-298 
39363—23-1 
