APPENDIX 457 



POTATO BAOTERIOSIS 



(Bacillus solanacearum, E. F. Sm.) 



A very distinct and well-marked bacterial disease of 

 potatoes has recently been observed in the north of Eng- 

 land and in Scotland, and consequently requires a more 

 detailed notice than that given at p. 342. The disease 

 has been recognised for some time in the United States, 

 where it has been carefully studied by Dr. E. F. Smith. 

 A marked characteristic of the bacterium causing this 

 disease is the production of a brown colouring matter in 

 the tissues attacked, hence the course of the disease can 

 be clearly followed in the haulm and tubers. 



The presence of the parasite is first indicated by the 

 wilting and shrivelling of the leaves. Soon afterwards 

 dark brown streaks may be seen in the stem. These dark 

 streaks gradually extend downwards, and pass along the 

 underground branches into the tubers. Once in the tuber 

 the disease shows as an imperfectly formed pale-brown 

 ring, situated at some little distance from the outside of 

 the tuber. As the disease progresses the brown ring 

 becomes broader and darker in colour, until finally only 

 the skin remains, the entire starchy portion of the tuber 

 having crumbled to powder, and the myriads of bacteria 

 it contained set free in the soil, where they live until an 

 opportunity is offered for infecting a fresh crop. 



Tomatoes and egg-plants also suffer severely from this 

 disease in the United States. 



Preventive Means. — The leaves or stem are, as a 

 rule, first inoculated, the bacteria gradually following the 

 vascular bundles of the stem down into the tuber. In 

 some instances infection of the tubers may occur directly 



