200 The Potato 



Bacterial milt 



Bacterial wilt, caused by the bacterium Bacillus 

 solanacearum, is a disease that affects potatoes, tomatoes, 

 eggplants and a few other solanaceous plants. It occurs 

 mostly in the southern United States. The vines wilt sud- 

 denly, often on a single stalk, but later affecting the entire 

 plant. The stems lose their bright green color and be- 

 come shriveled and blackened. The vascular tissues, at 

 an eariy stage, have a brown color somewhat similar to 

 that described for Fusarium wilt. This color can be 

 seen through the outer cells and extends upward as nar- 

 row black streaks, even out upon the leaf petioles and 

 vines. When such stems are cut across, tiny drops of 

 liquid ooze out of the vessels at the cut surface. These 

 are of a dirty or yellowish white color, but not sticky or 

 foul smelling. Examination with a microscope shows 

 them to be swarming with bacteria. 



This discoloration of the stem extends downward into 

 the stolons and tubers. A section across an infected 

 tuber at the stem end usually shows a blackening of 

 vessels, making a dark ring around the cut surface of the 

 tuber near the periphery. Bacteria similar to those 

 found in the stem are present in these vessels of the tuber 

 and later invade the other tissues, finally rotting the 

 entire inside of the tuber. 



The bacillus is carried from infected to healthy plants 

 by insects that infest the potato vines. Probably this 

 is the common means of dissemination. Control, there- 

 fore, would consist in destroying the insects as far as 

 possible and in the early removal of infected plants from 

 the field. 



