A METHOD OF OBTAINING ABUNDANT SPORULA- 
TION IN CULTURES OF MACROSPORIUM 
SOLANI E. & M. 
L.. O. KUNKEL 
Bureau of Plant Indusiry, U. S. Department of Agriculture 
Although the early blight fungus, Macrosporium solani, often 
fruits abundantly when growing as a parasite on potato leaves, it 
usually does not bear very many spores when grown in pure culture. 
Jones (4) reports that some of his cultures when old fruited rather 
freely. Jones and Grout (5) state, however, in their technical de- 
scription of the organism as Alternaria solani (E. & M.) Sorauer that 
it sporulates “sparsely in pure cultures.”’ 
Enough spores may be obtained by growing it in the ordinary way 
on culture media to test its parasitism to the potato plant. Galloway 
(3) performed this experiment as early as 1893 and Jones (4) repeated 
it a few years later. Nevertheless, the failure to obtain spores in 
quantity from pure cultures has made it impossible to perform ex- 
tended infection experiments with this important parasite. 
The writer found M. solani doing considerable damage in the 
potato fields of Aroostook County, Maine, last August, and in the 
hope of obtaining a strain of this fungus that would fruit abundantly 
in pure cultures, a considerable number of isolations were made. 
Cultures were in each case made from single spores. The organism 
was isolated from fifty-four different potato plants selected at random 
in half a dozen potato fields in the vicinity of Presque Isle, Maine. 
All of these single-spore strains were grown on a number of different 
culture media, including potato agar, string-bean agar, prune agar, 
and glucose agar. The several strains showed considerable differences 
in the appearance of their growth in culture, but none of them pro- 
duced more than an occasional spore on any of the media tested. 
In a former paper the writer (6) has described a method of retarding 
the growth of Monilia sitophila (Mont.) Sacc. by lowering the vapor 
tension of the atmosphere above pure cultures. It was recalled that 
by checking the mycelial growth in this way the fungus could be made 
to fruit more abundantly than when grown in a moist atmosphere. 
In the hope that this method might serve to induce sporulation, 
cultures of MW. solani were subjected to like treatment. More spores 
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