CONTRIBUTIONS FROM THE WISLEY LABORATORY. 607 



XX.— BLOTCH AND STREAK IN POTATOS. 



By A. S. Horne, B.Sc, F.G.S., F.L.S. 



The forms of disease investigated here are those described and 

 figured for the first time in England, by the writer, in the Journal 

 of Agricultural Science* Both blotch and streak are tuber diseases 

 — the haulm is not affected — prevalent in England, Scotland, and 

 Ireland, and both may be merely phases of one disease, but the 

 matter has not yet been definitely and scientifically proved. 

 In both cases the typical disease cannot be detected with certainty 

 by external inspection : the tuber must first be cut open to show the 

 brown spots, blotches, or streaks that disfigure the flesh and render 

 the affected potatos unfit for human consumption and unsuitable 

 for use as " seed." 



It is not my purpose at this juncture to discuss the whole subject, 

 since it is hoped to present to this Journal an exhaustive Report on 

 the probable cause of blotch and streak, the geographical distribution 

 of these forms of disease, and suggestions for dealing with them at 

 a later date. The immediate object is to describe some experiments 

 recently carried out at Wisley, but in order to render the account 

 more intelligible the progress of the investigation since its inception 

 must first be briefly reviewed. 



In 1908 I received for investigation from Messrs. Sutton 

 a sack of the potato ' Sutton Flourball ' affected with internal 

 disease. This furnished the opportunity of studying the disease in 

 a single known variety. Quantities of tubers of other varieties were 

 soon received from other sources, but here the markings were in the 

 form of streaks (locally called " sprain "). Since diseased samples 

 could frequently be traced to consignments from Scotland, I utilized 

 a grant provided by the Royal Society for the study of the obscure 

 diseases of potato, to visit the potato fields of Scotland and to 

 make arrangements for a series of experiments. With the hearty 

 co-operation of Dr. W. G. Smith and Mr. W. Bruce, B.Sc, of the 

 East of Scotland College of Agriculture, and Professor J. W. H. 

 Trail, F.R.S., of Aberdeen University, several trial plots were 

 planned on land known to produce crops affected with " sprain," 

 and disease-free tubers of ' Duke of York ' from Aberdeenshire were 

 chosen for " seed." In the meantime I had secured the co-operation 

 of Mr. VV. G. McGowan, who carried out and reported upon a parallel 

 series of experiments in another locality. In each experiment a high 

 percentage of streak occurred in the crop from ' Duke of York.' 

 Horne, A. S., in Jour. Agr, Sci, iii, (1910) p. 322, 



