Nov. 1, 1915 Potato Tuber-Rots Caused by Fusarium Spp. 189 



in another part of this paper. This statement is based upon the results 

 of inoculation work with several strains- of F. oxysporum isolated from 

 various sources and includes two identified by Wollenweber — i. e., Nos. 

 1948 and 2413. (See p. 190 and PI. XV, fig. 3.) The following species 

 and varieties of the section Elegans were found to produce tuber-rot in 

 varying degrees : (i) F. oxysporum. (2) A related form which differs by 

 producing an abundant pionnotes on potato cyUnders. (See p. 206 and 

 PI. XV, fig. I, 2.). Morphologically this fungus is identical with 

 F. hyperoxysporum (21, p. 268), described as a cause of stem-rot of the 

 sweet potato (Ipomoea batatas) by Harter and Field (4, p. 287, 291). 

 The experiments thus far carried out indicate its biological identity — 

 i. e., F. hyperoxysporum isolated from Ipomoea batatas caused a similar 

 rot under the same conditions. (See p. 192.) (3) F. vasinfectum Atkin- 

 son, the cause of cotton wilt. (4) Its homologue isolated from wilt of 

 okra {Abelmoschus esculentus). The numerous forms of the section 

 Elegans type, many of which appear to be morphologically identical 

 but biologically different, require further study, and it is not proposed 

 to enter into a taxonomic consideration of these forms at this time, 

 (See p. 206.) 



It seems probable that F. oxysporum is incapable of readily penetrating 

 the wall of the xylem. When it enters the vascular ring of the tuber 

 from the wilting mother plant, it hibernates therein during the resting 

 period of the tuber and enters the sprouts with the renewal of vegetative 

 activity. At other times as a wound or lenticel invader, plenty of suit- 

 able nourishment is at hand, and it produces a dry-rot or a wet-rot, 

 according to the conditions of temperature and humidity. Possibly as 

 a wound parasite it is without incentive or opportunity to enter the 

 vascular ducts. 



Although Smith and Swingle (14) and Manns (7) did not differentiate 

 their F. oxysporum form F. solani and other species occurring on potato 

 tubers, no evidence has been deduced to show that they were not in the 

 main dealing with the effects of a single species or to prove that F. 

 oxysporum does not cause a tuber-rot. 



Further notes on F. oxysporum as a cause of tuber-rot are given under 

 "Jelly-end rot" and in the experiments. 



INOCULATION OF POTATO TUBERS WITH FUSARIUM OXYSPORUM, FUSARIUM HYPER- 

 OXYSPORUM, AND FUSARIUM VASINFECTUM 



Fusarium oxysporum Schlecht. — F. oxysporum 2997; isolated on 

 March 10, 1914, from a tuber affected with stem-end ring disease and 

 vascular necrosis, from Everest, Kan. Culture used, i6-day-old pion- 

 notes on stem of Melilotus alba. As indicated in Table I, all tubers of 

 the four varieties Jersey Peachblow, Idaho Rural, Early Rose, and 

 People's were rotting after 19 days' incubation at an average temper- 

 ature of 23.1° C. (See PI. XV, fig. 3.) The least affected variety 



