A METHOD OF OBTAINING ABUNDANT SPORULA- 



TION IN CULTURES OF MACROSPORIUM 



SOLANI E. & M. 



L. O. KUNKEL 



Bureau of Plant Industry, U. S. Department of Agriculture 



Although the early blight fungus, Macrosporiiim 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 AUernaria 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. NeverthelCvSs, 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 M. solani were subjected to like treatment. More spores 



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