SILVER SCURF, A DISEASE OF THE POTATO. 



19 



This disease was called " Fleckenkranklieit " and also " Phellomyces- 

 Faule" by Frank in 1897 and 1898, respectively. It can hardly be 

 considered a spot disease, since it very often involves the whole 

 surface of the diseased tuber. Recently it has been shown by Appel 

 and Laubert that PlieUomyces sclerotiopJiorus, the fungus described 

 by Frank, is only the sclerotial stage of S pondylocladium atrovirens. 

 This fact naturally excludes the possibility of using the name applied 

 to this disease by Frank. More recently the disease under consider- 

 ation has been called " scab," " dry rot," '' dry scab," and '' scurf." It 

 does not seem wise nor justifiable to apply the term "scab" to this 

 disease, since we already have 

 three or four different kinds of 

 scab. Furthermore, Spondylocla- 

 dium does not cause symptoms 

 comparable to those produced by 

 Oospora, Spongospora, and Chrys- 

 ophlyctis. As is well known, all 

 of these parasites cause hypertro- 

 phy and cankers of the tissues in- 

 fected. Such is not the case with 

 Spondylocladium. On the con- 

 trary, it causes the death and 

 shrinkage of the attacked cells 

 and tissues. The term "scurf" 

 has been applied by Clinton and 

 is doubtless a better name than 

 any used previously, because it is 

 less confusing and is more de- 

 scriptive of the symptoms of the 

 disease. The light, glistening, 

 silvery discoloration of the sur- 

 face of the washed potato due to the Spondylocladium infection 

 is a very common and characteristic symptom. In view of this fact 

 the name "silver scurf" is proposed for this disease. 



Fig. 4.— Sclerotia of silver scurf, (a) The surface 

 view of aa infected area, showing the sclsrotia 

 and their relation to the outer layer of cells. (6) 

 An isolated sclerotium, much enlarged, in the 

 early stages of germination. (After T. Johnson.) 



DISTRIBUTION OF THE DISEASE. 



Silver scurf has been known in Europe since 1871, when it was 

 apparently first found and described by Hertz in Austria. In 1897-98 

 it was reported in Germany by Frank as causing* a sort of dry 

 rot. Johnson in 1903 reported it as causing considerable dry rot in 

 Ireland and the following year it was reported in England by Smith 

 and Riea. Up to the present writing silver scurf has been reported 

 from only one locality in the United States. Clinton found it in 

 Connecticut "on a few tubers among the many varieties to be tested 



[Civ. IL'7] 



