MARKET DISEASES OF FRUITS AND VEGETABLES 25 



become brown, discolored mummies, although usually they become 

 decayed by blue mold. 

 (See 157.) 



Gray Mold Rot 



(Botrytis sp.) 



Gray mold rot is a minor storage and transit disease, which attacks 

 sweetpotatoes at low temperatures and high humidities. Infection 

 takes place through the ends of the sweetpotatoes or through wounds 

 elsewhere. Decayed tissues are moderately soft and grayish brown 

 and have a starchy odor. The causal fungus can grow well over a 

 wide temperature range, but it usually causes most damage at 

 moderately low temperatures. At the usual storage temperatures this 

 fungus may completely decay infected sweetpotatoes within 2 weeks. 



(See also Globe Artichokes, Gray Mold Rot, p. 6.) 



Growth Cracks 



A severe blemish of sweetpotatoes sometimes occurs in the form of 

 moderately deep lengthwise and crosswise fissures commonly called 

 growth cracks (pi. 16, C). Apparently any weather or soil condition 

 that causes irregular or interrupted development of the sweetpotatoes 

 may lead to this cracking. Thus a period of rapid growth due to 

 favorable moisture conditions following drought may result in the 

 development of the trouble. In some regions it has been noted that 

 the application of high-nitrogen fertilizers or stable manure tends to 

 induce growth cracks. 



Experimental tests have shown that some varieties of sweetpotatoes 

 are much more likely to produce growth cracks than others. The 

 Southern Queen was found particularly susceptible. 



Most growth cracks heal without becoming infected, but oc- 

 casionally sweetpotatoes have been found on the market with 

 fusarium rot and black rot following the cracks. 



(See 46.) 



Internal Break-Down 



Sweetpotatoes in storage sometimes develop a break-down of the 

 internal tissues ; in advanced cases affected specimens can be detected 

 by their light weight and spongy feeling. When such potatoes are 

 cut it is seen that the internal tissues are pithy or dry and spongy, 

 with cavities forming in the central parts of the roots as the tissues 

 separate (pi. 15, C) . At times the spongy tissues are white or light 

 yellow and of a cottony texture. 



Internal break-down is usually found late in the storage season 

 and is most prevalent in storages that have been kept warm and 

 too dry. 



(See 41, 46.) 



Java Black Rot 



(Diplodia tulericola (Ell. and Ev.) Taub.) 

 OCCURRENCE, SYMPTOMS, AND EFFECTS 



Since Java black rot apparently does not attack sweetpotatoes 

 until after they are harvested it is of economic importance only from 



