1920.] The Distribution of Wart Disease. 733 



THE DISTRIBUTION OF WART 

 DISEASE.- 



H. V. Taylor, M.B.E., A.R.C.Sc, B.Sc, 



Deputy Controller of Horticulture^ Ministry of Agriculture 

 and Fisheries. 



In the early history of potato growing, Kmited cultivation had 

 to a great extent kept the plant healthy, but when the natural 

 and necessarily distributed culture was superseded by extensive 

 field culture, the plant soon developed a tendency to diseases 

 of various kinds. Owing to forced cultivation and unnatural 

 propagation the plants were weakened, and their resistance to 

 disease became less and less. 



One reads of one disease after another attacking the crops 

 until in the disastrous year of 1845 there occurred the great 

 outbreak of potato disease (" BHght ") in the British Isles. It 

 was not until much later, however, that another and now con- 

 sidered serious disease of the potato, viz., Wart Disease, made 

 its appearance to any great extent in this country. 



Characteristics of Wart Disease. — It has been proved that 

 Wart Disease of potatoes is caused by the fungus Synchytrium 

 endohioticum. The characteristics of the disease are irregular 

 warts or cauliflower-like protuberances, which grow from the 

 eyes of the tubers and from buds on the rhizomes below ground. 

 These warts may be less than a pea in size, or as large or larger 

 than the tuber on v/hich they grow. 



Appearance of Plant. — A orowino- plant badly affected with 

 Wart Disease generally shows no special features to distinguish 

 it from other unaffected plants ; though occasionally some of 

 the lower leaves near the surface of the ground may be found 

 to have developed into spongy-like, yellowish-green masses. 

 These are modified leaves, and all stages are sometimes present, 

 from a distorted warty lump, to a thickened spongy leaf, still 

 bearing the unaltered leaf outline. On lifting a badly affected 

 plant some or all of the tubers are found to have similar warty 

 outgrowths, but the colour is yellowish, like the skin of the 

 potato. In the case of potatoes growing near the surface of 

 the soil, however, the wart may be pushed outside and develop 

 chlorophyll, and so become greenish. 



* Report of a paper read before the British Association for the Advance- 

 ment of Science, at Cardiif, on 24th August, 1920. 



