MARKET DISEASES OF VEGETABLES. 51 



and in western Nebraska, being especially severe in the 

 Early Ohio variety. It is prevalent in bruised or frozen 

 potatoes from Washington, Idaho, Nebraska and Colorado. 



Infection takes place through breaks in the skin of the 

 tuber. These may be brought about by cuts or bruises, by 

 freezing and by attacks of other fungi. The spores of Fusa- 

 rium are usually everywhere present in the soil, on the sur- 

 faces of tubers, and in storage places, so that any break in 

 the tuber skin is very likely to become infected. 



Control of this disease depends upon careful handling of 

 potatoes to minimize injury as far as possible. Because of 

 the rapid progress of the rot, it is advisable to dispose of 

 affected stock at the earliest opportunity. It is not profit- 

 able to ship severely affected stock. 



Ref. (37) ; (53). 



POTATO: LEAK. 



Cause: Fungi (Pythium debaryanum; sometimes Rhiz- 

 opus nigricans). 



Leak is marked at first by a brown discoloration around 

 wounds or bruised areas. The discoloration later becomes 

 extensive, and the entire interior of the potato may become 

 soft, and buff or light brown in color. Under pressure, the 

 affected tubers exude a brownish watery liquid, and dis- 

 eased tubers often leak badly. Potatoes affected with leak 

 are much more watery than those affected with the wet type 

 of Fusarium tuber rot. 



Leak has been reported only from the Delta lands of the 

 San Joaquin Valley of California and from Idaho. It does 

 not occur in cool weather, and is entirely checked by heavy 

 frosts. 



Infection takes place in the field, and tubers are infected 

 only through wounds, such as those due to fork injury or 

 the breaking off of second-growth knobs. Infection occurs 

 only in hot weather, but once the disease has gained a foot- 

 hold, it may devevlop at lower temperatures. 



Leak can be controlled by careful digging and handling 

 of the potatoes and sorting out of bruised and broken tubers. 

 In addition it has been found advisable to hold suspected 

 potatoes 4 days in the warehouse before shipment so that 

 the disease, if present, may develop and be more readily 

 detected. It is not likely to be a storage trouble after the 

 warm season. 



Ref. (28); (29). 



POTATO: BROWN ROT (SOUTHERN BACTERIAL WILT). 



Cause: Bacteria (Bacillus solanacearum). 



Brown rot may be indicated externally by a slight depres- 

 sion at the point of attachment of the stolon to the tuber, or 

 by gray discolored patches on the surface. Sometimes no 

 external symptoms may be visible. Upon cutting infected 

 tubers, a moist brown discoloration and slight softening of 



