[Crown Copyright Reserved 



ROYAL BOTANIC GARDENS, KEW 



BULLETIN 



OF 



MISCELLANEOUS 1 ^FORMATION 



No. 



[1919 



XXL— THE SKIN SPOT DISEASE OF POTATO 



TUBERS. 



(Oospora pustulans.) 

 (With Plate.) 



M. Nest Owes 7 , 



The disease known as Skin Spot is one of the minor diseases of 

 potato tubers, and one which has never been thoroughly investi- 

 gated. It is essentially a disease which develops in storage, a 

 fact which probably accounts for its having been so long over- 

 looked and so little understood. In certain seasons, however, 

 Skin Spot is very abundant, and it appears to be becoming more 

 prevalent than formerly. The affected tubers are dotted over 

 with small dark spots, which are at times so numerous as to 

 weaken or even to kill the eyes, and by disfigurement, to. lower 

 the market value of the tubers. 



In the following paper a description of the causal fungus, which 

 proves to be a new species of the genus Oospora, is given, together 

 with an account of its growth in pure culture, infection experi- 

 ments, and notes as to the effects of the disease on the tubers 

 Although there is room for further work to be carried out with 

 regard to the Skin Spot disease and the causes contributing to its 

 development, it is thought that the results obtained should be 

 placed on record, especially since no detailed account of the 

 disease exists, and the identity of the fungus causing the disease 

 was quite unknown. 



Historical. 



Carruthers seems to have been the first botanist clearly to 

 distinguish Skin Spot. In March, 1904, he received some 

 potatoes from Lincolnshire, which he states were covered with 

 numerous bluish black warts (Journ. Roy. Agric. Soc. of 

 England, Vol. 65, 1904, pp. 261-262, fig. 2 A-E). When thinly 

 peeled a dark brown patch was found below each wart, and when 

 crowded together the patches became confluent. On dissecting 

 these patches, the cells of the potato were found to be permeated 



(587.) Wt. 168— 829. 1,125, 9/19. J. T. & S., Ltd. G. U. Sch. 1 





