1920.] Skin Spot Disease of Potato Tubers. 



THE SKIN SPOT DISEASE OF POTATO 



TUBERS. 



(Oospora pustulans.) 

 The following is an abridged and slightly modified account 

 of a paper by Miss M. N. Owen on the Skin Spot disease of 

 potato tubers. The research was carried out in the Ministry's 

 Laboratory for Plant Pathology at the Royal Botanic Gardens, 

 Kew, and the original paper was published in the Kew Bulletin of 

 Miscellaneous Information, No. 8, 1919. As this httle-known 

 disease appears to be on the increase, and as it is capable of 

 causing considerable damage to the eyes of " seed " potatoes, it 

 is thought advisable to reprint a portion of the article and one 

 of the illustrations. For technical details the reader is referred 

 to the full paper. 



*♦♦*♦* 



Introductory. — The disease known as Skin Spot is one of the 

 minor diseases of potato tubers, and one which has never been 

 thoroughly investigated. It is essentially a disease which 

 develops in storage, a fact which probably accounts for its 

 having been so long overlooked 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 this article 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. 



External Appearanco of the Disease. — The external characters 

 of " Skin Spot," although not very striking, are quite dis- 

 tinctive, and there is not much hkehhood of confusing it with 

 other " spots." When a large number of potatoes are ex- 

 amined it becomes apparent that the spot may assume a some- 



