186 orton: pathology of solanum tuberosum 



1. Potato wilt due to Fusarium oxysporum (Schlecht.) Sm. & 

 Sw., a disease widespread in the central and southern United 

 States but not yet proved to exist in Europe. 



2. Potato wilt due to Verticillium albo-atrum, a disease occur- 

 ring in the northern United States, in Great Britain and northern 

 Europe. 



3. Potato rosette and other troubles caused by Rhizoctonia, 

 especially prevalent in the western United States. 



4. Leaf roll, an inheritable, probably non-parasitic disease pre- 

 valent in Europe and parts of America. 



5. Curly dwarf, an inheritable, non-parasitic disease found both 

 in Europe and America. 



Leaf roll (Blattrollkrankheit) is a disease characterized by 

 an upward rolling of the leaves, by a decreased yield of tubers and 

 by transmission of the diseased condition thru tubers planted. 



The rolling of the leaves is the most constant and conspicuous 

 symptom of this disease. The leaflets curl or roll upward on their 

 midrib, often assuming a nearly tubular shape, and giving the 

 plant a staring appearance. This rolling is sometimes restricted 

 to the upper leaves, while in other cases all or nearly all of the 

 leaves on the plant exhibit it. This type of roll is distinct from 

 the curly leaf condition but a very similar roll may be induced 

 by other causes, such as wet soil, "black leg" and other diseases. 



The color of the foliage changes with the advent of leaf roll, 

 but these color symptoms vary greatly, from cases where the 

 leaves assume an unhealthy, light green color to those marked by 

 pronounced yellowish, reddish or purplish colors. 



The time of onset is early as compared with Fusarium wilt. 

 The effect on the plant is to check development. There is a 

 lessening or cessation of growth. The duration of life of the 

 plant, in some cases appears to be shortened by leaf roll, but 

 in comparison with the rapid death of American potatoes attacked 

 by Fusarium wilt the leaf roll is very slow in the action. 



The endurance of the seed piece as a character of leaf roll is 

 an interesting point frequently mentioned in the German litera- 

 ture, and is considered by Appel to be one of the symptoms of 

 leaf roll. The effect of leaf roll on the tubers is strongly marked. 



