4 BULLETIN 64, U. S. DEPARTMENT OF AGRICULTURE. 



In the same year there occurred in eastern Colorado, western Nebraska, 

 and adjacent districts a very serious outbreak of a potato disease 

 which was at the time locally attributed to Fusarium (Fitch, C. L., 

 in numerous newspaper articles). 



The many discrepancies and confused points in the description of 

 these diseases as presented in the European literature, in comparison 

 with American conditions, were further cleared up by the study 

 in 1912 of disease phenomena in a collection of seedling varieties 

 grown in Maine and New York by Prof. William Stuart, of the 

 Bureau of Plant Industry. Pure types of several of these troubles 

 were presented, thus greatly facilitating their diagnosis and differ- 

 entiation. 



A visit to several other potato centers in Wisconsin, Minnesota, 

 Colorado, Utah, Idaho, and California assisted in verifying the con- 

 clusions reached, which are given in detail in this bulletin. 



Briefly stated, it appears that several distinct diseases have been 

 confused to a greater or less degree by both American and European 

 writers, and the widely differing opinions and results are due to the 

 fact that none of the investigators had seen conditions in all the 

 countries. In particular, the American and European troubles had 

 not been compared. , 



In the present article several types of • disease are to be distin- 

 guished as of some importance, at least in the United States, viz: 



Fusarium wilt. — A disease characterized by the wilting or prematuring of the 

 plant, accompanied by a browning of the vascular bundles of stem and tuber, which 

 are infected by Fusarium oxysporum, (Schlecht) Sm. and Sw. Widespread in 

 America, but not yet identified from Europe. 



Vertidllium wilt. — A wilt resembling the foregoing, often more rapid and with 

 fungus mycelium higher in the stem. Due to Vertidllium albo-atrum Reinke and 

 Berth. Described by Reinke and Berthold in 1879. Present in both America and 

 Europe. 



Leaf-roll. — An inheritable disease marked by rolling of the leaves, reduced yield, 

 and other symptoms. Probably not due to a parasite. Common in Europe and 

 lately appearing in America (Blattrollkrankheit). 



Curly-dvjarf. — An inheritable, nonparasitic trouble in which dwarfing of the vascular 

 elements is a prominent characteristic. Found in Europe and America (Krau- 

 selkrankheit) . 



Rosette. — A stunted or dwarfed condition of the potato associated with injuries 

 (jf the underground stems and roots caused by the fungus Rhizoctonia; most con- 

 spicuous in the western United States. 



Mosaic. — A pathological condition marked by a mottling and distortion of the 

 foliage. Not previously described, but present in Europe as well as America. 



It is not unlikely that future studies will enable us to add still 

 other diseases to this group, and it may become convenient to differen. 

 t iate more types of leaf-roU and of curly-dwarf from within the rather 

 vnde limits established in this paper. 



The disease described by Appel as bacterial ring disease should be 

 mentioned. It appears that in Germany this was formerly confused 



