Nov. 24, 1923 
Variations in Strains of Rhizopus nigricans 
371 
SUMMARY 
1. Eighteen strains of Rhizopus nigricans have been studied. The 
organisms used were isolated from hosts widely separated botanically. 
They were obtained from various parts of the United States and from 
Europe. 
2. They were all found to be about equally parasitic on sweet potatoes. 
3. The optimum temperature for the germination of the spores was 
about 31 0 C., with the exception of one organism (4652) which had an 
optimum somewhat lower. The maximum was between 33.5 0 and 
35-5° C., with the exception noted above, which had a maximum close 
to 31 0 C. The spores of some of the organisms germinated at i.8° C. 
4. The optimum temperature for mycelial growth was about 26.2° C. 
and the maximum near to 31 0 C., with the exception of strain 4652, in 
which case both the optimum and maximum temperatures were slightly 
lower. The results show that the spores will germinate at a temperature 
several degrees higher than that at which the mycelium will grow. 
5. None of the strains produced a cell-wall-destroying enzym (pecti- 
nase), at least in sufficient quantity to be detected by the methods 
used when grown on sweet-potato decoction. 
6. With one exception, the acidity of the substrate (sweet-potato 
decoction^ was decreased. 
literature CITED 
(1) Harter, L. L., and Weimer, J. L. 
1921. A COMPARISON OP THE PECTINASE PRODUCED BY DIFFERENT SPECIES OF 
Rhizopus. In Jour. Agr. Research, v. 22, p. 371-377, 2 fig. 
(2) -. 
1922. Decay of various vegetables and fruits by different species of 
Rhizopus. In Phytopathology, v. 12, p. 205-212. Literature cited, 
p. 212. 
(3) - and Adams, J. M. R. 
1918. Sweet-potato storage-rots. In Jour. Agr. Research, v. 15, p. 
337-368, pi. 21-27. Literature cited, p. 366-368. 
(4) La Rue, Carl D., and Bartlett, H. H. 
1922. A demonstration of numerous distinct strains within the nominal 
species Pestalozzia guepini Desm. In Amer. Jour. Bot., v. 9, 
p. 79-92. References, p. 92. 
(5) Lauritzen, J. I., and Harter, L. L. 
1923. Species of Rhizopus responsible for the decay of sweet potatoes 
in the storage house and at different temperatures in infec¬ 
tion chambers. In Jour. Agr. Research, v. 24, p. 441-456, 1 fig. 
Literature cited, p. 456. 
(6) Matsumoto, Takashi. 
i92i. jL Studies in the physiology of the fungi. XII. Physiological 
specialization in Rhizoctonia solani Kuhn. In Ann. Mo. Bot. 
Gard., v. 8, p. 1-62, 6 fig. Bibliography, p. 58-62. 
(7) WeimEr, J. L., and Harter, L. L. 
1923. Hydrogen-ion changes induced by species of Rhizopus and by 
Botrytis cinerea. In Jour Agr. Research, v. 25, p. 155-164. Litera¬ 
ture cited, p. 163-164. 
( 8 ) -. 
1923. Temperature relations of eleven species of Rhizopus. In Jour. 
Agr. Research, v. 24, p. 1-40, 23 fig. Literature cited, p. 39-40. 
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