1 88 Journal of Agricultural Research voi. v, no. s 



of species of Fusarium occurring on the potato, they chose the name of 

 the earliest one for their fungus — i. e., F. oxysporum Schlechtendahl, 

 1824. This species was not differentiated from F. solani (Mart.) Sacc. 

 and other species occurring on potatoes; although no inoculations are 

 recorded by Smith and Swingle, F. oxysporum has been generally 

 accepted as the cause of both the wilt and the dry-rot. 



Manns (7) made inoculations with a species of Fusarium isolated from 

 the blackened vascular ring and one from dry-rotting tubers, confirming 

 the work of Smith and Swingle (14). He writes as follows (7, p. 316): 

 "In the infection work both of the organisms were wilt producing, 

 bringing about symptoms quite typical with that of the Fusarium blight 

 in the field." Tuber- rot as a result of inoculation with a pure culture 

 of his F^isarium sp. is not recorded. Like Smith and Swingle (14), he 

 did not consider F. oxysporum different from F. solani. 



Wollenweber (19, 20), after a study of F. oxysporum obtained from 

 the vascular system of vines and tubers, was convinced that this specifes 

 causes the wilt and stem-end ring discoloration, but not a tuber-rot. It 

 simply winters over in the stem end of the tubers. A few quotations 

 show his view regarding this species of Fusarium : 



* * * the fungus [F. oxysporum], a typical xylem inhabitant does not entirely 

 destroy the tuber without the help of tuber rot Fusaria or bacteria [20, p. 42]. 



The fact that F. oxysporum causes the wilt of growing potato plants and only uses 

 the xylem of the stem end of tubers for overwintering, without producing a rot of 

 the parenchyma, leads to interesting comparisons * * * [20, p. 42]. 



Referring to this fungus in his diagnosis, he states that it is a "* * * 

 vascular parasite, cause of wilt disease, but not tuber rot, of Solarium 

 tuberosum" (20, p. 28). 



To facilitate the arrangement of the species, Wollenweber (19, p. 32) 

 established six provisional sections of the genus Fusarium based upon 

 physiological and morphological characters. One of these sections, 

 Elegans, comprises the vascular parasites, including F. oxysporum. 



In general, Wollenweber's views in regard to F. oxysporum as indi- 

 cated above are supported by the writer, but the experience of the last 

 year indicates that these statements should be somewhat modified. 

 The repeated isolation of F. oxysporum and related forms of the section 

 Elegans from tubers rotting in field and storage, accompanied by the 

 failure in many such cases to obtain any other organisms capable of 

 producing a rot, indicates something more in the nature of this organism 

 than passive hibernation in the vascular ducts of the stem end of pota- 

 toes. That the latter may be the chief role of the strain of F. oxysporum 

 which causes wilt is not doubted. But there are strains of F. oxysporum 

 and related forms present in stem-end ring disease and dry-rot which 

 entirely destroy ^ the tubers under the experimental conditions outlined 



1 The fact that F. oxysporum is capable of destroying potato tubers is confirmed by Dr. Lon A. Hawkins, 

 of the Bureau of Plant Industry, in unpublished studies on the chemistry of rots of Fusarium spp. He 

 employed F. oxysporum 3395, a reisolation of strain 2413 (see p. 190). 



