MARKET DISEASES OF VEGETABLES. 65 



SWEET POTATO: STEM ROT. 



Cause : Fungi (Fusarium batatatis and F. hyperoxy- 

 sporum). 



In stem rot the end of the root is light and shriveled, and 

 the interior has a deep brown color and a peculiar cinna- 

 mon odor. Usually, however, stem rot is not plainly visible 

 externally, and the disease manifests itself merely by a dis- 

 colored ring, and at times by a secondary ring, visible in 

 transverse sections of the root. If the outer part of the root 

 is carefully removed, the discolored parts appear as a net- 

 work of brown fibers surrounding the heart. 



Stem rot is of widespread occurrence in all sweet potato 

 districts. 



This disease causes a wilt of vines in the field, and re- 

 duces the yield. Infection of the roots takes place in the 

 field, and the disease progresses only slightly in storage. 

 Stem rot is found infrequently in the market, and is de- 

 scribed here principally to avoid confusion with freezing 

 injury, which it somewhat resembles. 



Ref. (24). 



SWEET POTATO: MISCELLANEOUS DISEASES. 



DRY ROT. 



Cause: Fungi (Fusarium species). 



This disease is comparable to the Fusarium tuber rot of 

 the Irish potato. It is marked by shrunken areas showing 

 discolored flesh, and usually starts at one end of the root. 

 Dry rot is not common or of much importance. 



FOOT ROT. 



Cause : A fungus (Plenodomus destruens) . 



This is a storage rot of some importance. It follows a 

 blighting of plants in the field. It is a firm brown rot with 

 pimple-like protuberances on the surface. Foot rot may 

 enter roots through wounds and bruises and thus cause some 

 loss in storage. 



Ref. (27). 



NEMATODE DISEASE. 



(See Nematode Disease). 



TOMATO: ANTHRACNOSE. 



Cause: A fungus (Colletotrichum phomoides). 



In its early stages, anthracnose is characterized by small, 

 circular, sunken spots of the same color as the sound tissue. 

 These lesions enlarge rapidly, become watersoaked and 

 more sunken, and bear pinkish spore heaps which often 

 coalesce to form a slimy layer. These spore heaps or acer- 

 vuli turn black at times and resemble the pycnidia of Phoma, 

 so that anthracnose may be mistaken for Phoma lesions. 

 However, the spore heaps never are as definitely rounded as 



