May IS. 191S Seedling Diseases of Sugar Beets 141 



between them. The Phyllosticta cultures employed were supplied by 

 Miss Venus W. Pool, of the Rocky Ford (Colo.) field station. Pool and 

 McKay (34), who worked with Phoma cultures isolated by the writer from 

 decayed sugar beets, found them capable of producing the characteristic 

 leaf spots as readily as cultures isolated from the Phyllosticta pycnidia. 

 The fungus, however, is not an aggressive leaf parasite, but does its 

 greatest injury on the root. 



SOURCES OF INFECTION 



The source of original infection appears to be the seed. It has been 

 generally recognized in Europe for years that seed infection with Phoma 

 betae is universal. As American growers are using European seed 

 almost exclusively, it follows that the disease is constantly being intro- 

 duced into the United States on seed. A very large number of samples 

 of both European- and American-grown beet seed have been examined 

 for the presence of this and other pathogenic forms. With the excep- 

 tion of one single lot of seed, the examination of 100 seed balls by the 

 seedling method has invariably demonstrated the presence of Plioma 

 betae. Reexamination of this one lot, which was American-grown, 

 revealed the presence of the fungus in it also when larger samples were 

 tested. 



Frank (18, p. 180, 272-293) believed the fungus capable of living over 

 in the soil by means of its spores, but Peters (7, p. 278-286) holds that 

 it can do so only when fragments of beets are present to support mycelial 

 growth. A large number of trials of soil in America made by means of 

 seedlings growing in it from pasteurized seed indicate that Phoma does 

 not remain viable in the soil after the decomposition and disintegration 

 of its host. Field soils containing decaying beet fragments occasionally 

 yield cultures of the fungus in the spring of the first year following beets, 

 but, as a rule, even seriously beet-sick soils fail to give them. Samples 

 have been examined from Virginia, District of Columbia, Michigan, 

 Wisconsin, Kansas, Colorado, Utah, and California. 



MORPHOLOGY OF THE) FUNGUS 



Several hundred cultures of the fungus have been isolated and grown 

 upon media (Pi. XVII). No constant differences in cultural characters of 

 strains from the various sources have been observed. It is readily culti- 

 vated upon a great variety of media, although on many of these it 

 develops mycelium only. It fruits abundantly upon string-bean agar 

 (PI. XVII, fig. 2) and this medium has been used for purposes of identifica- 

 tion and for measurements of pycnidia and spores. It is evident that the 

 curves which might be plotted from the following tabulated results of 

 measurements would be irregular and consequently that they would 

 probably be changed by increasing the number of pycnidia and spores 



