Nov. I. I9I5 Potato Tuber-Rots Caused by Fusarium Spp. 187 



much alike, detailed accounts of the appearances presented are of doubtful 

 value and are eliminated. With every rot-producing species of Fusa- 

 rium included in the experiments the effect was essentially the same — at 

 minimum temperatures, a slow dry-rot; at maximum, a very wet rot, 

 with the tubers completely softened in two or three weeks. Sometimes 

 in the former a mycelium-lined cavity is developed, surrounded by a 

 zone of tissue appearing water-soaked — i. e., a zone of enzymic activity; 

 in other tubers at higher temperatures the same organism proceeds to 

 soften the tuber in a stratiform manner, the several layers reaching 

 across the tuber. Bad-smelling rots did not occur with the species of 

 Fusarium. Such rots associated with Fusarium spp. were found to be 

 mixed infections. When Fusarium spp. per se rot potatoes, an odor 

 suggesting ammonia and trimethylamin is developed. 



Rots caused by species of Fusarium are commonly spoken of as either 

 "dry-rots" or "wet-rots." The former are a result of comparatively slow 

 development at low temperatures. The experiments show that any 

 of these organisms capable of causing a rot work more rapidly in an 

 environment of optimum temperature accompanied by high humidity, 

 the tubers developing a wet-rot (see p. 196). Upon drying out, the 

 condition would be termed a "dry-rot." The two forms grade insen- 

 sibly into each other, so that neither term is specific. The examination 

 of potato tissues rapidly softening as a result of inoculation with pure 

 cultures of Fusarium spp. indicates that the middle lamella is dissolved 

 considerably in advance of the fungus; the hyphae ramify between the 

 cells, but do not appear to enter them at once. Ultimately the con- 

 tents of the cells are liberated, and the starch grains become more or 

 less corroded. 



It should be noted that the experimental data, revised and grouped 

 under the respective organisms, were obtained through a series of experi- 

 ments covering a period of more than a year. For example, the data 

 on F. oxysporum (see p. 191) were extracted from eight different experi- 

 ments which included several other species and show at a glance the 

 comparative effect of original and reisolated strains on different varieties 

 of potatoes at sundry temperatures. 



In the notes on the artificial inoculations recorded under the respective 

 organisms the history of the various strains is first outlined, followed by 

 a brief consideration of the results in text and tabular form. 



CERTAIN FIELD AND STORAGE ROTS OF POTATO TUBERS 

 AND THEIR CAUSE 



TUBER-ROT CAUSED BY FUSARIUM OXYSPORUM AND FUSARIUM HYPER- 

 OXYSPORUM 



In a study of a wilt and dry-rot of Solanum tuberosum, Smith and 

 Swingle (14) attributed both manifestations to a species of Fusarium. 

 After a consideration of the incomplete nature of previous descriptions 



