Diseases of the Potato 203 



diseases, but they may also be found within the central 

 area of the cut surface. They may be found throughout 

 the length of the tuber or be confined to the stem end. 

 The exterior appearance of the tuber gives but little 

 indication of conditions within. The vines also become 

 affected, but the symptoms have not been studied care- 

 fully enough to differentiate them from those of wilt 

 disease. No organism has been found associated with 

 the streaks in the tubers, but an organism has been found 

 associated with affected stems and roots. Affected tubers 

 should be discarded for planting as they may produce 

 weak plants, but they are not unfit for food. The same 

 or a similar disease is known in England as "Sprain" 

 and in Germany as " Eisenfleckigkeit." 



Curly dwarf 



Curly dwarf is a non-parasitic disease characterized 

 by a wrinkling and curling of the leaf-blade about the 

 veins and midribs. Affected plants are usually dwarfed 

 and die earlier than healthy ones, though all stages of the 

 disease may exist in a field, and in some plants it may be 

 so slight as to be hardly noticed. The yield in advanced 

 cases is very much reduced. Tubers from affected 

 plants, while they show no evidence of disease when 

 planted, will produce vines that show a more advanced 

 stage of the disease. Since the presence of the disease 

 is partly responsible for reduced yields, no tubers from 

 affected vines should be planted. The elimination of 

 these can best be accomplished by inspection of the 

 vines in the field about blossoming time of the plant, at 

 which time affected hills should be removed or marked 

 for removal. 



