Mayis, I9IS Seedling Diseases of Sugar Beets 151 



serious fungous pests of the sugar beet eliminated from its territory. 

 Since sugar companies have absolute control over the sources of seed 

 supply of their growers, it is quite possible for a company producing even 

 a portion of its own seed to maintain an area of quarantine within any 

 portion of its territory where it does not compete with other companies 

 for acreage, provided table beets and mangel- wurzels are not allowed to 

 bring in the infection. 



RHIZOCTONIA 



The genus Rhizoctonia has been used to include a group of sterile 

 fungi, more or less closely related morphologically. Much confusion 

 exists regarding the identity of the various forms, and there is likewise 

 great diversity of opinion as to the pathogenic properties of the members 

 of the group. To make clear, especially to foreign investigators, the 

 identity of the fungus under consideration in this paper, a brief discus- 

 sion of the literature seems essential. The name "Rhizoctonia" was 

 first applied by De Candolle (8) in 1815 to a fungus on alfalfa. He 

 eventually distinguished three species, R. crocorum, R. medicaginis , and 

 R. mali. During the following 35 years various workers described a 

 series of diseases caused by similar fungi, which were referred to this or 

 other genera. In 185 1 Tulasne (43, p. 188) united the known forms of 

 Rhizoctonia into one species under the name "Rhizoctonia violacea." 

 This classification has been followed by many workers. 



In 1858 Kiihn (27, p. 222-249) pubHshed an account of three species, 

 R. solani, R. medicaginis, and R. crocorum. He distinguished between the 

 two forms first mentioned by the difference in appearance of the sclerotia, 

 those of R. solani being smooth, and those of R. medicaginis, woolly. 

 He mentions R. medicaginis as being parasitic on the beet and carrot, 

 as well as alfalfa, and states that the fungus produces a reddish brown 

 or purplish color in the cells of the beet. 'This is the first mention of 

 Rhizoctonia on the beet, and it is likewise the first mention of the fungus 

 in Germany. Saccardo has included Kiihn's species under R. violacea, 

 while Giissow (21), who described a disease on potatoes and alfalfa in 

 England due to Rhizoctonia, considers R. solani Kiihn to be identical with 

 R. violacea Tul. Eriksson (14) in 1903 published the results of inocula- 

 tion work on various hosts, including the sugar beet. He designated his 

 fungus as R. violacea, but later reclassified it as Hypochnus violaceae (Tul.) 

 Eriks. (15, p. 421-430). He believed there were biological forms of it, 

 since the form on carrot attacked the beet with more virulence in the 

 second generation than in the first in which it was carried on that host. 



Atkinson (i) in 1892 described a damping-off of cotton due to a 

 sterile fungus later classified as Rhizoctonia. Balls (2, 3) has found 

 the same disease in Egypt, and Shaw (42) has more recently reported it 

 from India. In the meantime Duggar (10, p. 344) described the same 

 fungus as a damping-off parasite of the sugar beet, and Pammel (30) 



