58 U. S. DEPARTMENT OF AGRICULTURE. 



Generally the discoloration is restricted to the heart of 

 the tuber, but frequently it radiates to the exterior as well. 

 It may also appear on one side of a potato if this was ex- 

 posed to a stove in a railroad car or in the storage house. 

 The discolored regions may appear in zones in the periph- 

 eral parts and may be absent or less evident in the center. 

 In advanced stages, the affected tissue dries out and forms 

 cavities. In case cavities develop, these may be differenti- 

 ated from true hollow heart by their black lining of killed 

 tissue. 



Exposure of potatoes in the field or in storage or transit 

 for a day to temperatures of 90 to 104 F. causes this 

 injury. Potatoes lying in a very hot soil or lying on the soil 

 after digging may show it. More generally the injury is 

 caused in stove-heated cars or by storing potatoes at 45 to 

 50 F. in piles deeper than 6 feet. In stove-heated cars, the 

 injury usually is most severe near the stove and at the top 

 of the load. 



Black heart injury predisposes affected tissues to slimy 

 soft rot. The heated, killed and watery tissues offer excel- 

 lent growing conditions for bacteria. 



Black heart does not impair the food value of non-affected 

 tissues. 



Prevention of this injury in cars involves proper ventila- 

 tion, protection of the load near the stove with tin sheeting, 

 and careful attention to the fire. The temperature should 

 never go over 60 or 70 F. 



The injury can be prevented in storage places by provid- 

 ing proper ventilation and by storing tubers in piles not 

 deeper than 6 feet. 



Ref. (1); (68). 



POTATO: SCALD. 



Cause : Exposure to the hot sun. 



Scald on potatoes may appear first as large blisters which 

 soon become sharply depressed or as slightly bleached areas 

 with a very irregular and lobed margin of a darker metallic 

 color. Upon cutting such a tuber, it is found that a shallow 

 surface layer of tissue has been killed. This killed tissue is 

 dull gray in color, and is separated from the uninjured tissue 

 by a brown and very irregular line. The killed tissue, if not 

 infected, dries out and becomes tough and leathery. 



In many cases, more of the tuber is involved, both in sur- 

 face area and depth of the killed tissue. This type has been 

 tentatively named "deep scald," and shows much more dis- 

 coloration than the ordinary scald. Bluish black patches 

 often surround the lenticels, and the killed tissue darkens 

 very rapidly when cut surfaces are exposed to the air. 



Scald differs from late blight tuber rot in that the affected 

 tissue is not brown in color, and in the sharp line of demarca- 

 tion between the dead and the living tissue. Scald differs 

 from freezing injury in its much more irregular surface out- 



