194 



Potato Diseases 



Sprain. 



Sprain has caused considerable loss to potato-growers within the 

 last few years, affecting certain varieties in the field crop, often rendering 

 the yield practically unsaleable. 



Sprain includes two forms of tuber-disease — blotch (internal disease) 

 and streak (sprain) which have not yet been proved identical. Blotch, 

 under the name internal disease, is reported to have been under investi- 

 gation by Marshall Ward nearly twenty years ago but I have been 

 informed by Prof. Seward that Marshall Ward left no records of such 

 investigation. The word sprain, as used in the north, is applied to 

 tubers with internal, brown, streak-like markings. This word has been 

 adopted by the Board of Agriculture to include both blotch and streak. 



Fig. 4. Sontion of a tulK-r shuwiny internal disease or blotch. 



Under the name of Buntwerden or EisenHeckigkeit, sprain has long 

 been known on the continent of Europe and recognised as a distinct 

 disease not caused by fungal organisms. In Britain blotch and streak 

 were supposed by some authors to be either directly or indirectly due 

 to the late blight fungus and by others to the dry rot organisms. These 

 suppositions, however, as the writer^ has recently shown, cannot be 

 upheld. 



The importance of ascertaining whether the disease is caused by an 

 organism from the practical point of view is evident since the question 

 of the infection of croj)s is involved. Disease might arise from planting 

 diseased tubers or owing to the presence or transference of infected 

 soil. Frank considered that Buntwerden was due to the prevailing 

 conditions of soil and climate but his point of view is founded upon the 

 ' A. y. Hornc in Jour. Agric. Science, in, Pt. ',i (1!)1()). 



