INFLUENCE OF TEMPERATURE ON THE PECTINASE PRO¬ 
DUCTION OF DIFFERENT SPECIES OF RHIZOPUS 
J. L. Weimer and L. L. Harter 
(Received for publication April 28, 1922) 
Investigations (1) have shown that the following species of Rhizopus 
with the exception of the last two are parasitic on the sweet potato: nigri¬ 
cans Ehrnb., reflexus Bainier, tritici Saito, artocarpi Racib., delemar (Boid.) 
Wehmer and Hanzawa, maydis Bruderl., nodosus Namysl., oryzae Went and 
Pr. Geerligs, arrhizus Fischer, microsporus v. Tieg., and chinensis Saito. 
These fungi produce an enzym which dissolves out the middle lamellae 
so that the cells lose their coherence, thereby transforming the potatoes 
into a soft, watery mass. The cells themselves, however, are not pene¬ 
trated, at least in the early stages of decay. It was likewise shown (2) that 
the two nonparasitic as well as the parasitic species produce an enzym, 
a part of which is exuded into the substrate which macerates raw sweet- 
potato disks in from two to four hours. The nonparasitic species actually 
produce more enzym than some of those which cause decay of sweet po¬ 
tatoes. Furthermore, it was found that the maximum strength of the 
macerating enzym both in the solution and in the mycelium is reached after 
a two or three days’ growth of the organisms in sweet-potato decoction. 
Harter, Weimer, and Lauritzen (1) showed that these species of Rhizopus 
could be roughly grouped into high-, medium-, and low-temperature forms. 
The results demonstrated that a low temperature is not so much a limiting 
factor to infection and decay as a high temperature, since intermediate 
forms produced decay under laboratory conditions at relatively low temper¬ 
atures, while the low-temperature forms did not infect sweet potatoes at 
a temperature of 30° C. or above. 
In view of the relationship found to exist between the different species 
with respect to the temperature at which they will infect and decay sweet 
potatoes, the writers proposed to determine (1) if pectinase is produced 
at any temperature at which the fungus will grow, and (2) if the amount 
produced is greatest at the optimum temperature for infection and decay. 
Method of Experimentation 
The methods employed are, for the most part, the same as those pre¬ 
viously described by the writers (3), but modified when necessary to meet 
the requirements of the problem. The fungi were grown on sweet-potato 
decoction in 2-liter Erlenmeyer flasks held in incubators maintained at 
constant temperatures of 9 0 , 20°, 30°, and 40° C. The organisms were 
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