276 DISEASES OF ECONOMIC PLANTS 



leaves, which are usually light colored, assume a dull, un- 

 healthy appearance, with rolling or curling of the margins. 

 Progressive disease gradually causes the top to fall, and 

 gives a general effect of premature ripening. When the 

 diseased plants are pulled up, the roots are found to 

 be partly dead, quite brittle, and frequently bearing a 

 white or pink mold. When the underground portion of 

 the stem is cut across, a pronounced brown discoloration is 

 visible. This brown stain is also found in the branches 

 leading to the tubers, and a thin slice across the stem end of 

 the tuber will often reveal its presence there as well. 



The loss caused amounts to millions of dollars annually, 

 due: (1) to deficient germination; (2) to early ripening and 

 thus to diminished yield; (3) to dry rot in storage. 



When the potatoes are dug, there is rarely any external 

 evidence of the disease on them. The major portion of the 

 crop produced from wilted plants is nevertheless infected. 

 If these potatoes are stored in a cold place, but little change 

 occurs; but when infected potatoes are kept in a heated 

 room or left outdoors in a warm climate, a dry rot soon 

 develops. 



Beginning at the stem end the tuber shrivels, the inside 

 becoming brown and light in weight. Occasionally bacteria 

 cause a secondary soft rot, which proceeds more rapidly. 

 An early form of this dry end rot is frequently met with 

 shortly after the potaoes are harvested. Potatoes thus af 

 fected are known to buyers as ''jelly ends." 



The presence of this disease can be detected in otherwise 

 normal tubers only by making a thin slice across the stem 

 end and searching for the brown discoloration. Such pota- 

 toes are not desirable for seed, but are not objectionable for 



