618 JOURNAL OF THE TIOYAL HORTICULTURAL SOCIETY. 



ON POTATO " LEAF BLOTCH " AND "LEAF CUEL." 

 By A. S. HoRNE, B.Sc, F.G.S. 



During a recent visit to Scotland I found three distinct cases of a 

 leaf blotch disease, of which one, fortunately under control, proved 

 exceptionally severe. In each case the potatos originally used for 

 planting were imported from the Continent, and belonged to the 

 variety known as ' President. ' 



In the first case the grower obtained seed potatos from Holland 

 in 1909. In the crop resulting from this material he noticed a number 

 of stunted plants with yellowish foliage and blotched leaves. When 

 the crop was lifted, he found that the tubers borne by diseased plants 

 were few in number, exceedingly small, and generally below the 

 average size of potatos used for planting. It occurred to him, there- 

 fore, to save only the larger tubers, selecting by this means a large 

 proportion of tubers produced by apparently healthy plants. These 

 potatos were planted on the same farm in 1910. I saw the plants 

 obtained from them in September and noticed a large proportion of 

 diseased ones. The grower stated that the disease was quite as 

 bad as it was in 1910, or even worse. The proportion of bad plants in 

 the crop had not decreased, although, in all probability, most of the 

 tubers borne by plants with diseased foliage in 1909 had Been rejected. 

 There was no sign of this disease among plants of other varieties grown 

 in the same field. 



The second case, to which my attention was drawn by Dr. W. G. 

 Smith and Mr. W. Bruce, of the East of Scotland College of Agri- 

 culture, is of exceptional interest. It occurred on a potato field in 

 the Edinburgh district. Amongst other varieties of potato grown in 

 this field were two lots of the * President,' situated in adjacent plots. 

 These, when the farm was visited about the middle of September, 

 were especially noticeable. All the plants of one lot were exceptionally 

 strong and healthy and, from the appearance of the tubers, gave 

 promise of a good crop, whilst those of the other lot were without 

 exception unhealthy, and produced tubers of very small size. Upon 

 inquiry it was found that one lot of * Presidents ' had been grown from 

 seed potatos saved from a crop raised in Forfarshire and the other 

 lot from a crop raised in Midlothian. The seed potatos from which 

 the crops in Forfarshire and Midlothian were grown originally came 

 from Holland. One lot was purchased in 1908, and it is believed 

 that the other lot was obtained in 1909; but there is some doubt as 

 to whether this really was the case or whether both lots were purchased 

 in 1908. It appears that only small tubers were used for planting 

 in the case of the bad ' Presidents.' These were, in all probability, 



