[Crown Copyright Reserved. 
ROYAL BOTANIC GARDENS, KEW. 
BULLETIN 
MISCELLANEOUS INFORMATION. 
No. 8] [1923 | 
XXVI.—THE CAUSATIVE ORGANISM OF SKIN 
SPOT OF POTATOES. 
W. A. Miniarp and SYDNEY Burr. 
Since the first description of Skin Spot in scientific literature 
there has been considerable discussion as to the identity of the 
causative organism of this disease. The most complete study 
of the disease is that of Owen(7) (1919) from whose paper the 
following brief historical summary is taken :— 
In 1904, Carruthers(+), describing the Skin spot pustules as 
“bluish black warts”, isolated a fungus from which he was 
unable to obtain any fructifications whereby it could be identified. 
In 1915, Pethybridge(§) suggested Spicaria solani as the 
causative agent, whilst Milburn & Bessey(*) attributed a disease 
apparently identical with Skin spot to Spicaria nivea. + Lastly, 
Giissow(?) (1918) stated the opinion that the disease was of 
physiological and not microbic origin. 
The result of Miss Owen’s investigation was to give the 
Wollenweber(11), who does not appear to be acquainted with the 
English work on the subject, published an account of “ Die 
Pustelfiiule ’’ which, from his description and illustration, is 
obviously the same as Skin spot. He attributes this disease 
to Phoma eupyrena and finds a similarity between it and the 
‘Dry Rot associated with Powdery Scab” described in 1916 
by Melhus, Rosenbaum and Schultz(*) and ascribed by them to 
Phoma tuberosa. The last contribution to the discussion is that 
of Shapovalov(!9) (1923) who makes the startling announcement 
that Skin spot, as such, does not exist, but that the pustules of 
the disease are a primary stage of Corky Scab (Spongospora 
subterranea). The importance of such a statement 1s only 
realised when we remember how very common the pustules of 
the disease have become of recent years on the seed potatoes of 
many of our best-known varieties. 
z (78)20373 Wt396—P 32 1000 3/23 E&S A 
