JOURNAL OF ACR1COLTORAL RESEARCH 
Vol. XXX Washington, D. C. May 1, 19257No79 
THE INFLUENCE OF TEMPERATURE ON THE INFEC¬ 
TION AND DECAY OF SWEET POTATOES BY DIFFER¬ 
ENT SPECIES OF RHIZOPUS 1 
By J. I. Lauritzen and L. L. Harter, Pathologists, Office of Cotton, Truck, and 
Forage-Crop Disease Investigations , Bureau of Plant Industry, United States 
Department of Agriculture 
INTRODUCTION 
Temperature is regarded as ail im¬ 
portant factor in the infection and 
decay of sweet potatoes. Rather 
specific instructions regarding the 
proper temperatures at which sweet 
potatoes should be stored are given in 
the various publications dealing with 
storage. The temperatures recom¬ 
mended for curing and storing vary 
somewhat, but in general are as follows: 
For curing, 26° to 32° C.; for storing, 
10° to 14°. Notwithstanding these 
recommendations, there is little infor¬ 
mation available regarding the relation 
of temperature to infection and decay 
by the various organisms responsible 
for the decay of sweet potatoes. 
Among the most important organ¬ 
isms which cause this decay are some of 
the species of Rhizopus. The following 
species were found by Harter, Weimer, 
and Lauritzen (3 ) 2 to be capable of 
decaying sweet potatoes: R. tritici 
Saito, R. nodosus Namysl., R. maydis 
Bruderl., R. oryzae Went and Pr. 
Geerligs, R. delemar (Boid) Wehmer 
and Hanzawa, R. arrhizus Fischer, R. 
reflexus Bainier, R. artocarpi Racib., 
and R. nigricans Ehrnb. 
Hanzawa (1) studied 14 species of 
Rhizopus, separating them into three 
thermal groups on the basis of such 
characters as the presence or absence 
of spore germination and the abund¬ 
ance of mycelial growth, and the 
presence or absence of fruiting on 
potato plugs at various temperatures 
and after different periods of time. 
He’ does not give the exact increments 
of growth with the rise in temperature 
or after different periods of time. No 
measurements are recorded. These 
three groups are as follows: (1) High- 
temperature group, Rhizopus oryzae, 
R. arrhizus Fischer, R. chinensis Saito, 
R. japonicus Vuillemin, R. tonkinensi 
Vuillemin, and R. batatas Nakazawa; 
(2) intermediate-temperature group, 
R. nodosus, R. tritici, R. kasanensis 
Hanzawa, R. trubini Hanzawa, and 
R. usamii Hanzawa; and (3) low-tem¬ 
perature group, R. nigricans. 
Weimer and Harter (7) made an 
intensive study of the germination of 
spores in sweet potato decoction and of 
the mycelial growth and fructification 
on potato agar of 11 species of Rhizopus. 
They likewise separated the species 
studied into three thermal groups. 
Their grouping is slightly different from 
Hanzawa’s and includes some species 
not studied by him and excludes others. 
The work of these authors resulted 
in the following classification: (1) High- 
temperature group, Rhizopus chinensis; 
(2) intermediate-temperature group, 
R. tritici, R. nodosus, R. delemar, R. 
oryzae, R. arrhizus, and R. maydis; and 
(3) low-temperature group, R. nigri¬ 
cans, R. microsporus v. Teig., R. re¬ 
flexus, and R. artocarpi. 
Their results show the maximum, 
optimum, and minimum temperatures 
for spore germination, mycelial growth, 
and fructification, the increments of 
growth with the rise in temperature 
and increments of growth after differ¬ 
ent periods of time. 
One difference between the two 
groupings is that Hanzawa places 
Rhizopus oryzae and R. arrhizus in the 
high-temperature group, while Weimer 
and Harter place them in the inter¬ 
mediate. This discrepancy is appar¬ 
ently not serious, for if Hanzawa’s 
data are examined, one finds as good 
reason for placing these species in the 
intermediate group as with R. chinensis; 
in fact, a better reason if one eliminates 
R. delemar, which Hanzawa in his 
table still retains under R. oryzae and 
which shows a wider temperature range 
for sporulation than does R. oryzae. 
R. chinensis is sufficiently different 
from all the other species in its tem¬ 
perature response to place it in a group 
1 Received for publication June 30, 1924; issued June, 1925. 
2 Reference is made by number (italic) to “Literature cited,” p. 810. 
Journal of Agricultural Research, *. Vol. XXX, No. 9 
Washington, D. C. May 1, 1925 
Key No. G-464 
19976—25f-1 
(793) 
