MARKET DISEASES OF VEGETABLES. 49 



Fusarium tuber rot appearing at the end of the tuber in the 

 long, white varieties of the Northwest, such as the Burbank, 

 is known as jelly-end, while that appearing in other parts of 

 the tuber, especially marked in the round varieties such as 

 the Rural, is known as "black field rot." These rots are 

 caused by Fusarium radicicola, which also causes a very soft 

 leaky rot and a dry, black stem-end rot of potatoes grown 

 in the southern half of the Mississippi Valley. 



Wounded or bruised surfaces which have become sealed 

 with starch or cork should not be confused with Fusarium 

 infections. Generally tuber rot starts in bruises and cuts. 

 During the early storage season, it is often impossible to 

 determine whether or not a bruise or cut will develop tuber 

 rot. Later in the season the presence of soft discolored 

 tissue or cavities lined with mycelium makes a diagnosis 

 much easier. 



The safest and surest methods of control are careful han- 

 dling of tubers to avoid cutting and bruising; sorting out of 

 bruised, broken, cut, diseased, and frozen potatoes; and 

 storing of tubers in a well-ventilated place at a temperature 

 between 36 and 40 F. 



Ref. (7); (37). 



POTATO: JELLY END ROT; BLACK FIELD ROT. 



Cause: A fungus (Fusarium radicicola). 



Both jelly end and black field rot are types of the Fusa- 

 rium tuber rot previously described. In jelly end rot, the 

 end of the tuber is shrunken and collapsed, while black field 

 rot is characterized by shrunken, collapsed, black to brown 

 areas occurring anywhere on the surface of the tuber. 



The diseased tissue underlying the discolored or shrunken 

 surface is soft, watery, and light to dark brown or black in 

 color, or it may be rather firm and black. Unlike powdery 

 dry rot, cavities generally do not occur in the affected 

 tissues. 



The moist condition of jelly end rot is not observed unless 

 the potatoes have just been dug or have been removed re- 

 cently from a car which sweated or became overheated in 

 transit. Generally, under market conditions, the disinte- 

 grated tissue dries out and resembles typical dry rot. Very 

 often stock affected initially with jelly end or black field rot 

 subsequently becomes affected with powdery dry rot, which 

 progresses rapidly in storage. 



These rots occur most commonly in Nebraska, Idaho, and 

 Pacific Coast potatoes. Jelly end rot is prevalent in the long 

 varieties such as the Burkbank type, while black field rot is 

 most clearly marked in the round varieties such as the 

 Rural. Without a cultural examination it is impossible to 

 differentiate at times between jelly end rot and so-called 

 dry rot of the end of the tuber caused by Fusarium species 

 other than Fusarium radicicola. 



