1 84 Journal of Agricultural Research voi. v. no. $ 



Conclusive work on species of Fusarium which produce tuber-rot with 

 sufficiently deUmited species dates from Appel and WoUenweber's funda- 

 mental work on the form genus Fusarium. During the progress of these 

 studies Wollenweber established the wound parasitic nature of Fusarium 

 coeruleum (Lib.) Sacc. and F. discolor, var. sulphiireum (Schlecht.) App. 

 and Wollenw., and the causal relation of these species to a definite type 

 of rot. Jamieson and Wollenweber in 191 2 (5) described an external 

 dry-rot caused by F. trichothecioides Wollenw. Wollenweber in 191 3 

 (19, 20) extended the list of species of Fusarium causing tuber-rot by the 

 addition of the following: F. ventricosum App. and Wollenw., 1910, and 

 F. rtihiginosum App. and Wollenw., 1910 [considered a synonym of 

 F. culmorum W. G. Sm., 1884, by Wollenweber, 1914 (21)]; F. suhulatum 

 App. and Wollenw., 1910, as a weak wound parasite under special con- 

 ditions; F. orthoceras App. and Wollenw., 1910, and F. gihhosum App. 

 and Wollenw., 1910, as probable causes of tuber-rot. 



Jamieson and WoUenweber's description (5) of the powdery dry-rot 

 caused by F. trichothecioides is the first description of a definite rot con- 

 clusively demonstrated to be caused by a species of Fusarium which is 

 sufficiently described in its normal ^ stages to insure certain identifica- 

 tion. However, Wilcox, Link, and Pool (17) published a description 

 one year later of the same disease and subnormal stages of the same 

 organism, for which they proposed a new name — i. e., F. iuberivorum 

 Wilcox and Link. The examination of material similar to that used by 

 Wilcox and Link from Alliance, Nebr., demonstrated that F. iuberivorum 

 is identical with F. trichothecioides. 



The increasing number of rotting tubers submitted to the Department 

 indicated the existence of several types of a rot not hitherto described 

 which were caused by species of Fusarium and focused the author's 

 attention during the past year on a laboratory study of these diseases. 

 The object of this paper is to demonstrate the parasitic nature of certain 

 species of Fusarium and to contrast these organisms and the resulting 

 types of deterioration with those already recognized. The economic 

 importance of these rots and the interest manifested by pathologists in 

 a general group of diseases caused by species of Fusarium suggested the 

 advisability of a comprehensive treatment of the species known to cause 

 decay as an aid to their diagnoses and ultimate control. 



The tuber-rots considered in this investigation are all of the stem-end 

 and wound-parasitic type. They are not sharply differentiated from 

 each other nor from those previously described as caused by the following 

 species: F. coendeum; F. discolor, var. sulphureum; F. trichothecioides. 

 After having made isolations from several hundred submitted specimens 

 of stem-end-diseased tubers and from many more rotting as the result 

 of wound and lenticel invasion or inoculation with known species, the 



' For a discussion of the idea "normal" as used in this paper, see Wollenweber (21, p. 2ss-2Sl)- 



